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Geotechnical Inputs - February 1974
i i E TECHNICAL • INPUTS j FEBAUAgY19T4 FIUNTINGTON BEACH PLANNING DEPARTMENT I.EIGIMTON-YEN � A111D ABBOCIArES CITY OF HUNTINGTON BEACH CITY COUNCIL JERRY.A.MATNEY,May., HENRY H.DUKE,_Vice Mayor TE©W.BARTLETT ALVIN M.COEN NORMA BRANDEL GIBBS N.JOHN V.V.GREEN DR.D©NALD D.SHIPLEY DAVID D.RDWLANC3S, City Administrator _ PLANNING COMIVIIMON _ EDWARD H. KERINS, chaitY+vo FRANK P. HI+CsOINS, Zres-chairman ROBERT_D-BA,TIL, JOSEPH P.BOYLE wtLLIAM J.GEIGER MARCUS M.PORTER KATHERINE L.WALLIN, RICHARD A.HARLOW,Secretary • A • • • E TECHNICAL INP TS FE BRUARY '1974 HUNTINGTON BEACH PLANNING DEPARTMENT LEIGHTON-YEN AND ASSOCIATES • GEOTECHNICAL INPUTS TABLE OF CONTENTS PAGE 1 .0 Introduction 1 1.1 Geotechnical Considerations in Planning 1 1.2 Purpose of Study 1 1. 3 Scope of Study 2 1.4 Methodology 2 1.5 Limitations 2 2 .0 The Geologic Setting 4 2.1 Regional Geologic Setting 4 2.2 Regional Geologic Structure 6 2. 3 Regional Seismicity 7 2.4 Local Geology 10 2.5 Local Seismicity 11 3.0 Geologic Problems 19 3.1 Fault Displacement 19 3.2 Earthquake Shaking 20 3. 3 Liquefaction, Lurching and Differential Compaction 28 3.4 Tsunamis and Seiches 32 3. 5 Peat and Organic Soil Deposits 37 3. 6 Expansive Clays 37 3. 7 Beach Erosion 38 3. 8 Land Subsidence 38 3. 9 Groundwater 39 • 4.0 Geotechnical Considerations for Land Use Planning 42 4.1 Land Use Capability Analysis 42 4.2 Recommended Geologic Considerations 46 5. 0 The Seismic-Safety Element 52 5.1 Safety Legislation 5,2 5.2 CIR Guidelines 15 5.3 Methodology 59 6. 0 Appendix A Glossary of Terms 60 B Selected References 64 C Aerial Photographs 69 :a I� • section 1 introduchon • i • • SECTION 1. 0 INTRODUCTION • 1 . 1 Geotechnical Considerations in Planning One of the great challenges that faces modern man is to properly balance his use of the land with the forces of nature. The rapid urbanization of Soutern California has not always allowed for full consideration of natural forces within the context of land use planning. Although geologic forces are part of what must be taken into consideration, geology and its application to urbanized areas are important to maintaining this balance. The geologic forces that are continually in the process of change �• move so slowly that man is barely able to detect them. Consequent- ly, they go unnoticed until some significant geologic event, such as an earthquake , occurs . An example was the San Fernando earthquake of February 1971 . Although not as powerful an earthquake as others of recent history, it was particularly significant because of its close proximity to the Los Angeles metropolitan area and the f resultant damage that occurred. While it is only recently that urban geology has been recognized as having significant impact on the long range planning process , its basic principles are known and able to be applied to compre- hensive planning. • 1 . 2 Purpose of the Study This study was contracted for by the City of Huntington Beach with the firm of Leighton-Yen and Associates to provide the Planning Department with technical geologic data for use in the General Plan program. Although primarily directed towards the Seismic Safety Element, the results of the study significantly affect the Open Space and Conservation and Land Use Elements . • 1 . 1 . 3 Scope of Study • This study represents an investigation and analysis of the following geologic factors within the Huntington Beach planning area as depicted in Figure 1-1 : 1 . Fault displacement 2 . Earthquake shaking • 3. Liquefaction, lurching and differential compaction 4 . Tsunamis and seiches 5 . Peat and organic soils deposits 6 . Expansive clays 7. Beach erosion 8 . Land subsidence • 9 . Groundwater Upon analysis of all the above factors , a summary geotechnical land use capability map was prepared that would provide assist- ance in land use planning decisions . • 1. 4 Methodology The study was primarily an accumulation of existing data from varied sources (refer to bibliography Appendix B) . No field investigations were part of this study. The data presented in • this report is not new; it does exist in one form or another . However, this is the first time it has been assimilated and comprehensively analyzed for the Huntington Beach planning area. • 1. 5 Limitations The data presented in this report is general . The scope of the study did not permit detailed field investigations . The data, especially the maps , should not be interpreted to be precise. It is sufficient for long range planning, however, and . detailed investigations that occur as part of the development process will more accurately define the data. As this data is accrued, it can be used to update the information presented in this report. Throughout this report wherever specific limitations exist on certain data, they are pointau out. • • 2 . r S y .. MdADOBJ • kb BOLSA EDOKW .;:.:4_ Y. i:.. WAINER HEIL .... ...................................... ....................... .. .. .. .................. ::.; ;i:�i SLATER . ...... ..y, .................. ......L!: n: ........... ........... �•::...:::::.::::...':::::::.::�:::.}7:.?!.xx'.:':':..'.•':'::�i:':':•:'iii:vi:::':<Ji..;.i;:.:;:,:;i:.:;:;:.':::�:.:..':':.�.:i'i.•il:'i`:':':':':.:.:':':::�:'i.':'.':':':�. .2 :;:� ::<:.:.i:.:.:...: s ........................... ...........................:. ............. ........................... ............:::v: .:....:w: . :::. ::.:........................ .. ' ?i:i �y�;.:ririrtiti'�' ..k... TAIRBtT c ::':.:':�:�:.:�is�:�::i s�i::::.:.;:.�:�:�i is�i;>:: @ s f • X. am i ?IC i v. i OAREIELD r.... ....................... .. \. >: ........... . wiw.pb✓r. �i:yC.:4:4?i::ir' - -TOWN • ADAMS / i j_5:;::::'v:::::i RJDIANAPOLIS tT , .: • O l ca .....{ J ATLANTA .L N Ca' b MAMLTON �y. . f...': . .... BOMM ?:s Figure 1-1 • PLANNING AREA huntington beach planning department • 3. section2 geobgic SECTION 2. 0 THE GEOLOGIC SETTING 2 . 1 Regional Geologic Setting The City of Iiuntington Beach lies very near the northern end of one of the major geomorphic provinces of coastal southern California: the Peninsular Range Province. (Refer to Figure 2 -1 Regional 4D Setting) The onshore portion of the Peninsular Range Province consists of elongated, northwesterly-trending mountains and valleys that extend over 900 miles from near the base of the Santa Monica Mountains to the southern tip of Baja, California. A considerable portion of • the Province, termed the Continental Borderland, actually lies submerged beneath the Pacific Ocean. The Los Angeles Basin is the northernmost physiographic unit within the onshore portion of the Peninsular Range Province. It is a gently-sloping coastal lowland 50 miles long by 20 miles wide. • The present, relatively flat floor of the Basin is interrupted in places by lines of low hills . The Basin is bounded on one side by the Pacific Ocean and on the others by steep mountain ranges . On the southeast side it terminates against the San Joaquin Hills in the vicinity of Newport Beach, California. • The Los Angeles Basin has been the site of almost continuous marine deposition of sediments from mid-Miocene time (15 to 20 million years ago) until about the beginning of late Pleistocene time (approximately 400,000 years ago) . A total of over 30 ,000 feet of sediment has been deposited over the older crystalline basement a 4 . • lie* 6abr;s/ Mf,& TRANSVERSE Fljq E P : " CE fl'I'lMill,life, NCR E A.-SITE R N •..::•:is ` I/"/1111"` Hills ` •• � ���"� �`I y 31J M�n�tb I—O gn'L��S �• `sl�`�1,1�f11=`,Illmr'I� �, r=:. ° PEN L A �� IJWrn Hills ,�,y� .• i,=p=ry^G .lr,nJQ �ry Gjl C� y �� 1 �•`���•'���� ':�r=�����:'.: Hens R.secnAs ills It 64 �`�":' (/ /her` '. •. v 4dt; C 1'MI �I O 4?y1 San4a a An 1111111f -: ,n ; P,lec t 1r ` r/ Vedas liil��'f Lon ei;i?;t.! lt., ► ►► ps. Vf N Bttah Jill HillP,9C \ /RACMills NCWP�rt')"IlewOcfl .Siruciurat Z.,\t +:=jfiee:e :1, r„4C _.::::; :; WAS ...,.'!t;l:flNk?fie:;:* S O >i ►o �::::..: Vie;llI(1:•j!!t• Figure 2-1 REGIONAL SETTING huntington beach planning department S. i rocks in the deepest portion of the Basin near the confluence of the Los Angeles River and Rio Hondo . Three major streams - the Los Angeles , San Gabriel and Santa Ana Rivers - all with few major tributaries head in the surrounding mountain ranges and drain southwestward across the Basin to the Pacific Ocean. Although surface flow near the mouths of these streams is common only during the winter months , they are associated with infrequent flooding. The City of Huntington Beach is located on the coast between the mouths of the San Gabriel and the Santa Ana Rivers near the southeast margin of the Los Angeles Basin. Bedrock beneath the City is similar in its general character to the surrounding bedrock of the Basin, consisting of from 8 , 000 to 161, 000 feet of Cretaceous (135, 000 , 000 years ago) to Recent (12, 000 years ago) sediments overlying a pre-Late Cretaceous basement complex of metamorphic and igneous rocks . If the bedrock beneath the City is common to that of the surrounding area, the manner and degree to which this bedrock has been broken and deformed is not , as discussed in the next section. 2 . 2 Regional Geologic Structure The northern onshore end of the Peninsular Range Province , in the vicinity of the Los Angeles Basin, is broken into three major crustal blocks by two northwest-trending active "basement" fault systems : • the Newport- Inglewood and the Whittier-Elsinore. (Refer to Figure 2 -1 Regional Setting) Movement on these basement faults has been continuing sporadically approximately since the Middle Miocene and is one of the chief factors responsible for the formation of the large structural • depression also referred to as the Los Angeles Basin. It is the continued downwarping of the Basin, in combination with uplift in the adjacent mountains , that has resulted in deposition of the great thickness of sediments referred to in the previous section of this report . Net earth movement due to faulting on both the Whittier-Elsinore and Newport- Inglewood Fault Systems tends to be • right-lateral strike-slip in nature (that is : overall movement occurs primarily in a horizontal plane with the northeast sides of the faults moving south and the southwest sides moving north) . Horizontal displacement on the Newport-Inglewood Zone since the Mid-Miocene possibly totals six miles . • The City of Huntington Beach is located directly astride the Newport- Inglewood Structural Zone (refer to Figure 2-1 Regional Setting) . Newport-Inglewood Structural Zone is a term used by earth scientists to describe the elongated zone of uplifted and 6 . complexly deformed sequence of sedimentary rocks in the Los Angeles coastal area that overlies a "master" fault in the crystalline basement complex at depth. The Newport-Inglewood Structural Zone ! extends from the Santa Monica Mountains at least as far as offshore Laguna Beach and possibly considerably further south (Richter, 1970 ; DWR, 1964 ; Emery, 1960) . In the Los Angeles Basin the zone is marked by a line of low hills and mesas as shown in Figure 2-1 Additional information concerning the characteristics of the zone is presented in Section 2 . 5. Local Seismicity. 2 . 3 Regional Seismicity For the purpose of the present discussion, it is significant to note that the Newport- Inglewood Structural Zone is associated with • both active faulting and historical earthquakes of moderate magni- tude. The relation between faulting and earthquakes has been illustrated several times by damage to oil wells , presumably due to subsurface faulting, during minor earthquakes . (Barrows , 1973; Hamilton, 1971) . Figure 2- 2 indicates characteristics of some of the more significant earthquakes known to be associated with the Newport-Inglewood Structural Zone , beginning with the 1920 event, which was the first earthquake definitely attributed to the Zone (Taber, 1920 ; Richter, 1970) . Epicenters are indicated in Figure 2-6 . Huntington Beach lies at the southerly onshore end of the Newport- Inglewood Structural Zone in an area where the Zone apparently undergoes a transition from being a relatively narrow zone of one or two active faults to a fault zone ten times as wide, containing . at least three active faults and a large number of faults tentatively classified here as "potentially active" (discussed further in Section 3. 0) . Although probably undergoing a geologically rapid evolution with regard to its tectonic conditions , within the next 100 years this structural zone can be expected to exhibit appre- ciably the same mode and level of activity as evidenced by the S historic, geologic and seismic records (Harding , 1973; Bandy, 1973) . Other faults of regional significance to the City are the Palos Verdes Hills Fault, the Norwalk Fault, the Whittier Fault, the Santa Monica-Raymond Hill Faults , the Sierra Madre Fault, the San Andreas Fault, and, to a lesser extent , the San Jacinto Fault. . The latter three faults have been associated with historic earth- quakes where there has been surface rupture due to faulting. The other faults and the Newport- Inglewood System as well , have not been associated with surface rupture. Yet they evidence varying degrees of on-going seismic activity and geologic evidence of recent 7 . FIGURE 2-2 haracteristics of some significant earthquakes associated with the iewport- Inglewood structural zone, excluding aftershocks . (Barrows , 973 ; Wood, 1966 ; DWR, 1964 and 1967) . SUMMARY OF DIRECTLY MAGNITUDE APPROXIMATE LOCATION ASSOCIATED DATE (RICHTER) OF EPICENTER DAMAGE/INJURY • June 21, 1920 4. 9 Inglewood, California Numerous building (Inglewood (estimated) failures and severe Earthquake) structural damage to poorly built struc- tures in localized • epicentral area. Sev- eral people injured, 1 killed. March 10 , 1933 6. 3 3. 5 miles offshore of Numerous building (Long Beach Newport Beach, Calif. failures , including • Earthquake) schools . Bridges , roads , utilities damaged. Damage in excess of $40 million. 120 people killed, hundreds injured. • Quake felt over 100,000 sq. mi . area. 4th most destructive earthquake in United States history. • October 2 , 1933 5. 4 Signal Hill, near Los Considerable minor (Signal Hill Alamitos , California damage. Earthquake) December 27 , 1939 4. 5 Huntington Park - Long Minor damage to struc- a Beach area, California tures and street lights . loctober 212 1941 5. 0 Long Beach, California Damage in West Domin- guez oil field. Minor damage to structures , ' especially in Gardena area. $10, 000 damage in Gardena. Adft • 8 . s November 14, 1941 5. 4 Long Beach, California 50 buildings severely damaged. Power fail- ures , damage to pipe- lines , storage tanks , 2 schools condemned because of structural damage . Approximately $1 million damage. June 18 , 1944 4. 5, 4. 4 Dominguez Gap Area, Minor property damage. near Compton, Calif. October 27, 1969 4. 5 1 . 5 miles offshore of Extent and type of Laguna Beach, Calif. damage, if any, (Most southerly earth- unknown. quake attributed to N-I Zone) • • • 9 . s faulting. None of the latter faults have been associated with earthquakes approaching the magnitude of the 1933 Long Beach Earthquake which occurred on the Newport-Inglewood System and had a Richter Magnitude of 6 . 3. Although the Sierra Madre Fault System has been associated with moderate-sized earthquakes (Mag. between 5 . 0 and 7. 0) and the San Jacinto and San Andreas Fault Systems with major earthquakes (Magnitude greater than 7. 0) , the effect of considerable distance mitigates their influence on the City of Huntington Beach. Additional details on the characteris- tics of the above mentioned fault zones are presented in Section 3. 0. 2 . 4 Local Geology The location and activity of the Newport-Inglewood Structural Zone throughout the recent geologic past has been one of the dominant controlling factors in the evolution of almost every aspect of the geologic environment in the City of Huntington Beach. Its influence has been prominent in the following areas : (1) local seismicity and earthquake hazards , (2) local bedrock deformation and petroleum accumulation, (3) distribution of earth units , (4) groundwater conditions , and (5) landform evolution. For a discussion of the implications of the presence of the Newport- i Inglewood Structural Zone on local seismicity and earthquake hazards , see Re Tonal Seismicity, Earthquake Shaking, Fault Displacement and Liquefaction. Primarily as a result of the intensive petroleum exploration effort within the City, subsurface geologic conditions are well known in their general aspects down to depths of about 10,000 feet. Structurally, the sedimentary bedrock beneath the City can be divided into three different regions : (1) a relatively simple faulted offshore anticline (see Glossary of Terms) , (2) a complexly folded and faulted central portion (the Newport-Inglewood Structural • Zone) , and (3) a relatively undeformed northeasterly-dipping flank on the northeast side of the Newport-Inglewood Structural Zone. Recent deposits (those deposited within approximately the last 15, 000 years) have been only slightly disturbed by faulting and folding. The North Branch Fault appears to give the clearest evidence of recent faulting based on information obtained from water wells in the Bolsa and Santa Ana Gaps . The faults exhibiting the next best evidence are the Bolsa-Fairview and South Branch Faults . Aft 10 . The recent geologic history of the Huntington Beach area is rather complicated and a brief summary follows , based partially on a discussion in California Department of Water Resources Bulletin t 63- 2 (1968) . During late Pleistocene (Wisconsin) time , base level of all streams in the area was lowered due to withdrawal and "storage" of vast amounts of water in the form of ice in the continental ice sheets. This resulted in renewed stream erosion, with the Santa Ana River cutting through the deposits being gradually uplifted .along the Newport- Inglewood Structural Zone , thus forming the mesas and gaps (refer to Figure 2-3 Fault and Geologic Conditions) . At the end of the Wisconsin glaciation about 15 ,000 years ago , sea level began to rise rapidly and coarse-grained stream channel sediments filled the gaps to a considerable extent. The rapid rise in sea level abated approximately 9, 000 years ago and the local stream regimen probably came to resemble today' s , resulting in the deposition of fine-grained floodplain deposits over the coarser alluvium. It is within the last 9 , 000 years that the Santa Ana River abandoned its previous courses (i.e. , through Bolsa Gap) + and became established close to its present location in the Santa Ana Gap. The fine-grained floodplain deposits form the uppermost "confining layer" (further discussed in Section 3. 9 Groundwater) above the fresh water-bearing sediments , as well as the present ground surface in the gaps . During this period of deposition, peat deposits formed in the gaps where dense , water-loving vegeta- tion became permanently established around gravity and artesian springs . Also during this period, a barrier beach formed, shelter- ing the inland lagoons and tidal marshes in which fine sand, silt , clay and organic muck were deposited. Details concerning the composition and structure of rock formations . and other characteristics of earth units in the Huntington Beach area are presented in Figure 2-3 Fault and Geologic Conditions and Figure 2-4 Characteristics of Near-Surface Earth Units . 2. 5 Local Seismicity A considerable amount of investigation has been conducted by various agencies with regard to understanding the basic nature of the Newport-Inglewood Structural Zone. Laboratory, seismic, subsurface and surface investigations have led to the classification of the zone as an area of "wrench faulting" or "wrench tectonics" . A wrench fault system in a geologically youthful stage of development is characterized by a relatively wide fault zone (commonly greater than one mile in width) with individual faults presenting a highly complex pattern of distribution and activity. One key feature of a "youthful" wrench fault system is the lack of any one, continuous , through-going fault on which all displacement and activity may be Adft 11 . FIGURE 2-4 CHARACTERISTICS OF NEAR-SURFACE EARTH UNITS CITY OF HUNTINGTON BEACH General Spatial General Significant Engineering Age Earth Units Relationships Characteristics Geology Properties Beach and Narrow barrier beach Loose , unconsolidated, Subject to rapid erosion, Dune Sand along coast extending fine to coarse-grained transportation $ deposit- up to 10001 + inland sands . Saline ground- ion by longshore currents ; from shoreline. water at shallow depth and waves, especially and subject to tidal during storms . Highly fluctuations , about permeable. 30 ' thick. z Recent Primarily intermixed Unconsolidated channel Channel deposits form � Alluvial $ stream channel and deposits composed of important freshwater moo Tidal Marsh floodplain deposits generally coarse- aquifer confined by Deposits with minor tidal and grained sands & overlying relatively lagoonal marsh gravels . Floodplain impermeable floodplain deposits in Santa Ana deposits composed of and tidal deposits . Gap. Primarily flood- fine-grained sands & Shallow aquifer subject plain deposits with silts with numerous to man-caused water- extensive areas of layers of peat. quality degradation. lagoonal and tidal Lagoonal & tidal Peat lenses compressible marsh deposits in marsh deposits of under moderate static Bolsa and Sunset Gaps . silty clays and loads . Shallow ground- clayey silts are water near coast . mixed with signifi- cant amounts of fine organic mud (muck) . About 125 ' thick. N General Spatial General Significant Engineering Age Earth Units Relationships Characteristics Geology Properties Older At surface in Newport , Unconsolidated to Permeable coarse-grained z Alluvial Huntington Beach and partially consolidated layers (aquifers) serve P4 Deposits Rolsa Chica Mesas , interlayered fine-and as important source of H o (Lakewood beneath recent coarse-grained sedi- fresh groundwater land- Qcn Formation) alluvial deposits ments . Marine & non- ward of Newport-Inglewood a w northeast of North marine silt-clay Structural Zone. Saline ►-� Branch Fault in layers 25 ' to 75 ' water predominates on a Bolsa Gap and north- thick in Bolsa Gap. seaward side. Shallow east of Adams Avenue Sand-gravel layers aquifers subject to in Santa Ana Gap. 50 ' to 100 ' thick in contamination from human Bolsa Gap. Maximum activities . Source of thickness in north sand and gravel in Huntington Beach Huntington Beach Mesa. approximately 400 ' . Contains numerous sea- shell middens of arch- w eologic interest. 7WO z w Marine Limited surface expos- Unconsolidated to Permeable sandy layers a o Deposits ure in a few localities partially consolidated serve as important source (San Pedro around margins of deposits . Predominant- of fresh water (aquifers) w w Formation) Newport $ Huntington ly sandy with silt and over entire area. a Beach Mesas . Buried silty clay interlayers. Partially protected from a beneath recent and About 240 ' thick along saline water contamination older alluvial crest of Newport- by overlying and inter- deposits in gaps and Inglewood Structural layered fine-grained, mesas . Zone. Thickens to impermeable sediments and north and south. various faults . Maximum thickness over 1000 ' near Santa Ana. w General Spatial General Significant Engineering Age Earth Units Relationships Characteristics Geology Properties Older Not exposed on land Partially consolidated Upper portion of formation w Marine within the City bound- predominantly fine- contains permeable beds w Deposits aries . Present at grained sediments . with fresh ground water. H U (Fernando depth everywhere with- About 1000 ' thick in Relatively minor oil a Formation - in onshore portion of area of Santa Ana production when compared a formerly City (within 300 ' of Gap . with deeper Early Pliocene "Pico" surface near Hamilton and Miocene units . Formation) Street) . Present (and possibly locally exposed) beneath ocean in offshore portion of City. • expected to occur (such as with the well-known San Andreas Fault) . Rather, stress relief is accomplished by correspondingly smaller • movement on any number of the relatively short, discontinuous and "intertwined" faults characteristic of wrench fault systems . The term "Newport- Inglewood Structural Zone" applies to the complex elongated zone of folds and faults present in the sedimentary bedrock beneath the Los Angeles-Orange County coastal plain. The localization of the structural zone in this area is thought to be due to the presence of a master fault in the crystalline basement rock that underlies the sedimentary bedrock of the Los Angeles Basin. movement on this master fault has placed continuing stress on the overlying sedimentary bedrock, which has responded by folding and rupturing in the complex "wrench" pattern discussed above. A simplified cross section, not to scale, is indicated in Figure 2-5 to illustrate one basic interpretation of the geologic data in this area. • This complex pattern of folding, faulting, and uplift as briefly described above has developed because of the inherent weakness (geologically incompetent) of the sedimentary rock sequence. This rock sequence has been able to absorb , within recent historic times , the stress placed upon it by internal adjustment (folding and faulting) at depth. • Stress has apparently not accumulated to the point where stress relief by surface faulting, as well as by faulting and folding at depth, has occurred. It is the opinion of Leighton-Yen and Associates , and that of numerous other geologists , that a point in time will be reached when earthquake-related stress relief will be accomplished by surface rupture on one and probably several of the surface faults within the Newport- Inglewood Zone. The City of Huntington Beach lies within the segment of the Newport-Inglewood trend wherein this surface rupture is expected. Because of the large number of • faults and folds within the zone, surface displacement on any one fault is anticipated to be minor, probably a matter of inches , though possibly greater than one foot in some areas . Displacement is expected to be complex and variable in nature, being combina- tions of different senses of dip and strike-slip. Overall displace- ment across the width of the zone is expected to have a dominant • right lateral sense . Overall right-lateral surface displacement across the width of the Zone could total several feet during a maximum probable earthquake. • • 15. • • Sl' IF. Pacific Newport- Inglewood Ocean Structural Zone • Sedimentary Bedrock • Crystalline basement + + + + ++—+ + v + + + + + + + + + + + + + "Master basement fault • • • Figure 2- 5 SCHEMATIC CROSS SECTION huntington beach planning department .� • 16 . • It is felt that surface displacement could be a feature of future earthquakes of lesser magnitude than the maximum probable event. The amount of expected surface displacement will vary with the S magnitude of the event , as does the intensity of ground shaking. The state of knowledge of subsurface geologic conditions beneath the City of Huntington Beach and the state-of-the-art does not permit accurate estimation of either the length or magnitude of future surface faulting to be expected from a given magnitude ,r earthquake occurring within the Newport-Inglewood Structural Zone. Adft i • If • • 17. • • FA AT • �y GARDEN G V • R .,� tl� � • .t� SEAL BEA�6 .� •''•.,1 r VX L IN • HUNTI NGTON BEACH j� .;:�' ... •••. MESA :'o NEW • a.s 0 BE CH sip a:o • Figure 2-6 Atak EPICMRS/FAULTS huntington beach planning department • 18. a • section 3 gedogiC problems • • • SECTION 3. 0 GEOLOGIC PROBLEMS • 3. 1 Fault Displacement The potential for fault displacement that extends to the ground surface is of particular concern in any seismic investigation • because it is impractical , and in some cases, not technically feasible to design and build a structure capable of withstanding ground rupture . Faults within the City of Huntington Beach determined to be geologically active and expected to be associated with ground • rupture at some time in the future are the North Branch, Bolsa- Fairview, and South Branch Faults ; all of these are faults within the Newport-Inglewood Structural Zone, as shown in Figure 3. 1 Fault Map. Surface rupture has apparently not occurred within the past 9, 000 years on these faults in the Huntington Beach area (DWR, 1966 and 1968) . This presumed fact , in addition to the absence of ground rupture occurring with an historic moderate-sized earthquake (1933, Magnitude 6 . 3, with a probable 30 kilometer length of subsurface rupture that extended entirely beneath the City of Huntington Beach) indicates that the probability is relatively low that surface rupture will occur within the next 100 years, even though one or more moderate-sized earthquakes may occur. The potential for surface rupture on the above-named faults is greatest where they occur from Bolsa Chica Lagoon to the northwest (including the Huntington Harbor area) . • • 19. 4*. Ota or ok 4,,, SP ^ ti ME, HIGHEST SEISMIC RISK ``s•.. a°` a (GREATEST SURFACE RUPTURE �, �q \ / /. •♦ �,� ,��� POTENTIAL WRHIN CITY M AREA OF INTENSIVE SHEAR �F' /�`.�`. oo```' o� • •• BURIED TRACE OF FAULT (WITHIN `� o •+�, \\ ©UNCERTAINTY AS TO EXISTENCE OR EXTENSION OF FAULT`000 o � e°ell .m 10 PAW jF FP •---� _ Q�. fr r e sPAF \ ff H FAQ -� 4. , w• ,. - i..a T� -„+,rr -.�,rr r+ 'r - --�.:..�r-r�+x-*•"'r � R • 7•• --• �, -��•- n�i-���```��,`�� � '����"a ��rbap�l rr wr `�� : �- 1 77 ♦� ` ram,+! ♦� y �\ W ANCH FAULT - ;' `► SOUTH- —" � rr.� .■ --- - .Ills- —r-aIW11R' 'w-rr+. irr r.r rI — � r__-.` T PACIFIC COAST - S4 FnV�•1 r rr-- >' - _ .. OLIVE — __. -�? - WALNUT ST. ? —. ULT--------- • SOURMLEIGHTON-YEN&ASSOC. 9-1-73 Afftk 3- 1 HUNTINGTON BE4CH CALIFORNIA PLANNING DEPARTMENT FAULT MAP • Information available to date appears sufficient to classify the remaining faults within the City as "potentially active", based on their presumed burial beneath 50 to 200 feet or more of undis- turbed or slightly disturbed recent sediments . It is felt likely that subsurface investigations in the Santa Ana Gap area would reveal one or several faults in that area now considered "potent- ially active" to actually be "active" to the same degree as the North, South and Bolsa-Fairview Faults . The apparent absence of surface faulting along the Newport-Inglewosd trend in the past few thousand years remains essentially unexplained. The explanation is felt to lie in the nature and various relation- ships in the geologic and seismic environments . The hypocentral depth of the 1933 Long Beach earthquake was approximately 10 kilo- meters . The earthquake originated well within the crystalline basement rocks as would be expected from the general tectonic setting of southern California. Apparently the thick sequence of relatively weak, saturated sedimentary bedrock between the crystalline basement and the ground surface can accommodate repeated large strains such as imposed by the 1933 event without surface rupture . The general nature of the deformation of the Newport- Inglewood Structural Zone would seem to support this hypothesis . Lack of recent surface faulting, gentle topography, and urbanization all tend to make fault location difficult. Although published sources agree as to the general location of buried fault traces , the plotted locations can be assumed to be only approximately correct, based on the most up-to-date information available, and as shown in Figures 2 . 3 and 3. 1 . 3. 2 Earthquake Shaking • Without regard to any other factor such as location of subsurface geology, it has been found universally that in most earthquakes , ground shaking accounts for by far, the greatest amount of damage and injury. As a recent example, over 990 of the damage caused by the 1971 San Fernando earthquake has been attributed to ground shaking effects . In a small percentage of earthquakes , ground rupture is responsible for a major amount of damage. Methods commonly employed for estimating ground motion for a particular site in California, and other areas where earthquakes are associated with surface faulting, begin with mapping major fault zones which are likely to influence the site and a determin- ation of the maximum probable earthquake likely to occur on these faults . One approach often used for estimating the maximum probable earthquake for a given fault is to use available geologic data and determine the maximum length of the fault and relate this to magnitude. In connection with this approach, it has not been observed that a particular fault will rupture along its entire length during a single earthquake. A maximum probable rupture • 20 . length equal to one-half the total fault length is considered to be a conservative assumption (Albee and Smith, 1966 ; Bonilla, 1970) . a Figure 3-2 Maximum Probable and Credible Earthquakes summarizes our "best guess" magnitudes for the "maximum probable" and "maximum credible" earthquakes for the various major active faults that are likely to contribute to strong ground shaking within the City of Huntington Beach. The methodology employed in determining these magnitudes is as follows : 1. Determine the total length of the fault from published geologic maps . 2 . Divide this length by 2 to find the probable maximum rupture • length associated with the maximum earthquake. This is based on the suggestion by Albee and Smith (1966) that the primary causal rupture at depth for the maximum earthquake which can be generated on a given fault has a maximum length of less than half the total fault length. 3. With the maximum probable rupture length, enter Figure 1 of Albee and Smith (1966) and determine the corresponding range of maximum earthquake magnitudes for the fault. 4. The lower value may be considered as the "first guess" for the maximum probable earthquake and the higher value as the "first • guess" for the maximum credible earthquake for that fault . 5. The "first guess" values are then compared with published expert opinions , if any, on the maximum probable and maximum credible earthquake magnitudes for the fault under study, a judgment factor applied, and "best guess" values determined. The maximum probable earthquake is one that is likely to occur with a fairly high probability. The maximum credible earthquake is one that is likely to occur with a finite probability. Figure 3-2 also lists the maximum historic earthquake magnitude associated with each fault zone. • Once the controlling faults are recognized and the maximum probable future earthquake for each fault is determined, procedures are available for estimating base rock and ground motion characteristics based on correlations of previous earthquake records and the distance to the causative fault . (Seed, Idriss and Kiefer, 1969 ; Schable and Seed, 1973 ; Housner, 1965 ; Matthiesen, et al , 1972 ; among others) . Unfortunately, at present there are insufficient records available to cover a wide range of possible soil and geologic conditions , earthquake magnitudes and distances from the causative fault. • • 21 . FIGURE 3- 2 MAXIMUM PROBABLE AND CREDIBLE EARTHQUAKES CITY OF HUNTINGTON BEACH Approximate Probable Maximum* Distance to Maximum Rupture Length Corresponding** City of Estimated Magnitude For Range of Maximum Maximum Huntington Total Fault of Maximum Maximum Probable Credible Beach Length Historical Earthquake Earthquake Earthquake Earthquak Fault Zone (miles) (km) Earthquakes (km) Magnitudes Magnitude Magnitude Newport- 0-3 90+ 6. 3 45 or less 6 . 6- 7 . 6 6 .6 7 . 6 Inglewood _ (1933) Whittier 21+ 103+ 3 . 2 51 or less 6 . 8- 7 . 7 6 . 8 7 . 7 (1971) Elsinore 25+ 180+ 5. 5 90 or less 7 . 2-8 . 0 7. 2 8 . 0 (1938) San Jacinto 50+ 310+ 7 . 1 155 or less 7 . 5-8 . 2 7. 5 8. 2 (1940) (Seven quakes of M greater than 6 . 0 since 1918) San Andreas 53+ 450+ 6 . 5 225 or less 7. 7-8 . 4 7. 7 8 . 4 (from Garlock (1948) Fault S/E) *Based on the suggestion by Albee and Smith (1966) that the primary causal rupture at depth for the maximum earthquake which can be generated on a given fault has a maximum length of less than half the total fault length. **Based on Figure 1 (Albee and Smith, 1966) . N N Most of the available data are for earthquakes of magnitude 6. 5 or less and for sites that were located 20 miles or more from the i epicenter or fault . Few records are available within 0 to 3 miles of the causative faults . Therefore, these procedures may be even less reliable in the prediction of ground motions immediately adjacent to the causative fault than that of greater epicentral distances . It appears that the 1933 Long Beach earthquake would provide a rational basis for establishing the ground motion characteristics to be used in connection with the minimum aseismic design of engineered construction within the City. Strong motion records for this event do not exist for any site within the City. However, strong motion records are available for the earthquake recorded at a Long Beach (9-1/2 miles) , Vernon (24 miles) , and Los Angeles subway terminal (27 miles) . The distances in parenthesis refer to the distance from the center of rupture, considered to be Sunset Beach, to the recording station. These and other existing records could provide the basis of an analytical solution using computer programs and dynamic soil properties . However, even these approaches would be subject to the selection of an appropriate scaling factor to be used to modify the existing records . Here again the absence of records close to the causative fault could affect the accuracy of analytical solutions . Figure 3- 3 summarizes the estimated ground and rock motion character- istics for the estimated maximum probable earthquakes . Based upon presently available empirical relationships , the maximum base rock accelerations could range from about 0 . 10g. to 0 . 65g. ; the maximum ground accelerations could range from about 0 . 18g. to 1. 0g. depend- ing on the causative earthquake . The high values of maximum base rock and maximum ground motion presented in Figure 3-3 for the Newport-Inglewood Fault should be interpreted in reference to the following constraints : 1. The data base from which accelerations are estimated does not include the effects of local soil conditions . 2 . Very few strong motion records are available for sites located within zero to three miles of the causative fault. 3. The determination of the magnitude of the maximum probable earthquake is primarily subjective and should require risk 40 analysis depending on the type of structure or development involved. In view of these apparent constraints in the state-of-the-art of empirical approach for estimating ground motion very close to the causative fault and since the maximum probable earthquake on the Newport-Inglewood Fault is expected to dominate the intensity of fi-�JP Adft 23. FIGURE 3- 3 ESTIMATED GROUND AND BASE ROCK MOTION CHARACTERISTICS MAXIMUM PROBABLE EARTHQUAKES CITY OF HUNTINGTON BEACH Estimated(1) Estimated(2) Predominant (3) Probable (4) Distance from Maximum Maximum Period of Duration of Causative Causative Estimated Base Rock Ground Base Rock Strong Earthquake Fault Magnitude Acceleration Acceleration Motion Shaking Fault (Miles) (Richter) (g) (g) (Seconds) (Seconds) Newport- Inglewood 0-3 6. 6 0 . 65+ 1 . 0 0 . 30+ 19 0 . 9 (4) Whittier 21+ 6 . 8 0 . 21 0 . 30 0 . 30+ 22 !Elsinore 25+ 7. 2 0 . 20 0 . 35 0 . 35+ 30 San Jacinto 50+ 7. 5 0 . 10 0 . 18 0 .45+ 40 San Andreas 53+ 7. 7 0 . 10 0 . 20 0 . 50+ 46 (1) Schnable and Seed, 1972 (2) Matthiesen, et al, 1972 (3) Seed, et al, 1969 (4) Geological Survey Circular 672 , 1972 N ground shaking in the City of Huntington Beach, another method for establishing minimum ground motion characteristics has been consid- ered. Analytical solutions to ground motion are beyond the scope • of this study. We, therefore, have attempted to estimate the ground motion at Huntington Beach due to the 1933 Long Beach earthquake on the basis of intensity. It is felt that the resulting values might provide the basis for developing a "ground spectrum" to be used for minimum aseismic design in lieu of other detailed. studies . • According to the isoseismal map prepared by the California Division of Mines and Geology (California Geology, March 1973) , the Modified Mercalli intensity for Huntington Beach was VIII for the 1933 Long Beach earthquake. • • • • w • • Aft e 25 . MODIFIED MERCALLI SCALE OF EARTHQUAKE INTENSITIES THE MERCALLI INTENSITY SCALE (As modified by Charles F. Richter in 1956 and rearranged) If nroa of these sects then the If~of these Veers then the are observed Intensity is. are observed lntewalty It: Earthquake shaking not felt.But people may ob- Effect on people.Difficult to stand.Shaking noticed serve marginal effects of large distance earthquakes by auto drivers. without identifying these effects as earthquake- I Other effects; Waves on ponds; water turbid with caused. Among them: trees, structures, liquids, mud.Small slides and caving in along sand or gravel bodies of water sway slowly,or doors swing slowly banks. Large bells ring. Furniture broken. Hanging objects quiver. Eject on people. Shaking felt by those at rest. Structural effects: Masonry D'.beavily damaged; VIU especially if they are indoors,and by those on upper It Masonry C• damaged, partially collapses in some floors. cases; some damage to Masonry B% none to Masonry A'. Stucco and some masonry walls fall. Effect we. people. Felt by most people indoors. Chimneys, factory-stacks, monuments, towers. Some can estimate duration of shaking. But many elevated tanks twist or fall. Frame Muses moved con may not recognize shaking of building as caused by III fooundations if not bolted down; loose panel walls 40 an earthquake;the shaking is like that caused by the thrown out. Decayed piling broken oft passing of light trucks Effect on people:General fright. People thrown to Other effects: Hanging objects swing. ground. Structural effects. Windows or doors rattle. IV Other effects. Changes in flow or temperature of Wooden walls and frames creak. springs and wells.Cracks in wet ground and ton steep slopes. Steering of autos affected. Branches broken . Effect an pwple.Felt by everyone indoors. Many from trees. estimate duration of shaking. But they still may not Structural efeas.Masonry D'destroyed;Masonry IX recognize it as caused by an earthquake.The shaking C' heavily damaged, sometimes with complete is like that caused by the passing of heavy trucks, collapse, Masonry B'is seriously damaged.General though sometimes, instead,people may feel the sen- damage to foundations. Frame structures, if not sation of a jolt, as if a heavy ball had struck the V bolted, shifted off foundations. Frames racked. walls. Reservoirs seriously damaged. Underground pipe Other effects: Hanging objects swing. Standing broken. t' autos rock.Crockery clashes,dishes rattle or glasses clink. Effect on people: General Panic. Structural efects.Doors close,open or swing.Win- J Other uffircls: Conspicuous cracks in ground. In dows rattle, areas of soft ground, sand is ejected through holes and piles up into a small crater,and.in muddy areas. Effect on people. Felt by everyone indoors and by water fountains are formed. g most people outdoors. Many now estimate not only Structural Sf'tcts. Most masonry and frame struc- the duration of shaking but also its direction and tures destroyed along with their foundations. Some is have no doubt as to its cause. Sleepers wakened. well-built wooden structures and bridges destroyed. Other rfects: Hanging objects swing. Shutters or Serious damage to dams, dikes and embankments. pictures move.Pendulum clocks stop,start or change VI Railroads bent slightly. rate. Standing autos rock. Crockery clashes, dishes rattle or glasses clink. Liquids disturbed, some Effect on people: General panic. spilled. Small unstable objects displaced or upset. Other effects: Large landslides. Water thrown on Structural cOkem- Weak plaster and Masonry D' banks of canals,rivers,lakes,etc.Sand and mud shif- • crack. Windows break. Doors close,open or swing J ted horizontally on beaches and flat land. XI Structural dko.General destruction of buildings. E,fa on people: Felt by everyone. Many are Underground pipelines completely out of service. frightened and run outdoors. People walk un- Railroads bent greatly. steadily. Other e$ecutss. Small church or school bells ring. Elect on people. General panic. Pictures thrown off walls,knicknacks and books off Other flans:Same as fior Intensity X. shelves. Dishes or glasses broken. Furniture moved Struerurst effects: Damage nearly total, the ulti- XII • or overturned.Trees,bushes shaken visibly,or heard VII mate catastrophe. to rustle. Other erects Large rock mama displaced.Lines of Structural orjk : Masonry D• damaged; some sight and level distorted. Objects thrown into air. cracks in Masonry C•.Weak chimneya break at roof s Maw►nry A: Good workmanship and mortar. reinforced line. Plaster,loose bricks,stones,tiles.cornices.un- designed to resist lateral Airces. braced parapets and architectural ornaments fall. Mast►ary 8: Goad workmanship and mortar, reinforced. Concrete irrigation ditches damaged. J Mo w►nry C: Good workmanship and na►rtar. wtreinfi►rced. Masc►nry D: Po for workmanship and ononar and weak materials. like sdobe. 26 . s However, in some areas around Compton, which were underlain by saturated alluvium, the intensity was considered to be IX. It is therefore likely that the intensity within the tidal marsh areas : of Bolsa Gap and Santa Ana Gap was also IX. On this basis , the following intensity distribution has been selected as reasonable for the 1933 Long Beach earthquake. 1933 Long Beach Earthquake Probable Modified ;Mercalli Intensity Location IX Low areas within Sunset Beach, Bolsa and Santa Ana Gaps , within one mile+ of coast and areas of a peat and organic soils . VIII - IX Inland areas of recent alluvium more than one mile from coast with intensity decreasing with increasing distance from coast. 40 VIII Higher elevations of Bolsa Chica Mesa and Huntington Beach Mesa. Rough correlations between Modified Mercalli intensity and peak ground acceleration and velocity are available. For peak ground velocity, the relationship as stated by Esteva and Rosenblueth (1964) is expressed by the following equations : I = log 14v log 2 where I = M.M. Intensity v = peak ground velocity, cm/sec. The peak ground velocities corresponding to Modified Mercalli intensities of VIII and IX are 18 and 37 cm/sec. , respectively. The range of ground accelerations for M.M. intensities of VIII and IX taken from 'Nuclear Reactors and Earthquakes , TID-7024 , United States Atomic Energy Commission, 1963 and Newmann (1954) are tabulated below: 27 . Modified Mercalli Ground Acceleration ( ) Intensity TID-7024 Neumann VIII 0.15 to 0 . 35 0. 27 IX 0. 35 to 0 . 70 0. 53 Neumann's relationship is based on a correlation between peak ground acceleration, as measured with a strong motion seismograph, and Modified Mercalli intensity for ten earthquakes between 1933 and 1949 in the western part of the United States . Using Matthiesen' s (1972) empirical relationship between earthquake magnitude, peak ground velocity, and distance to the fault , a magnitude 6 . 3 earthquake may be expected to produce a peak ground velocity of 63 cm/sec. very near to the fault. Therefore , if scaling factors of 0. 28 and 0 . 59 are applied to Matthiesen' s relationship, peak ground velocities of 18 and 37 cm/sec. will be obtained. t If the same scaling factors are applied to Matthiesen's relationships for peak acceleration, a rough correlation between Modified Mercalli Intensity and peak acceleration can be obtained. This was done, and the results are presented in Figure 3-4 , along with the results from the TID- 7024 and Neumann's relationships . The values in Figure 3-4 may be used as a rough guide in formulating a "ground spectrum" to # provide a basis for minimum aseismic design at various locations within the City. The ground acceleration value to be used in a given case would depend on the importance of the structure . For example, in # designing a hospital or school , the upper limit of the range may be appropriate, whereas a single-story, wooden frame structure may be designed on the basis of the lower value. The values presented in Figure 3-4 are considered to be tentative and subject to modi- fication as improved relationships and procedures become available . '• Newmark (1969) has demonstrated that "response spectra" can be estimated simply by multiplying the ground spectrum by amplification factors which depend on the damping of the structure . These amplification factors are indicated in Figure 3- 5. 3. 3 Liquefaction, Lurching and Differential Compaction During an earthquake, the resulting ground shaking will tend to compact loose deposits of cohesionless soils . If the soils are saturated, the compaction process will result in an increase in the pore water pressure in the soil . With the increased pore 28 . • • • • • • • a • • • FIGURE 3-4 ESTIMATED PEAK GROUND MOTION FOR 1933, P4AGNITUDE 6 . 3 LONG BEACH EARTHQUAKE IN CITY OF HUNTINGTON BEACH Modified Peak Ground* Peak Ground Mercalli Velocity Acceleration Location Intensity In Sec. (g) A. Low areas within Sunset Beach, IX 15 0 . 6+ ** Bolsa and Santa Ana Gaps within one mile+ of coast and areas of 0. 35 to 0 . 70 *** peat and—organic soils . 0 . 53+t B. Inland areas of recent alluvium VII -IX 7-15 0 . 3 to 0 . 6 ** more than one mile from coast with intensity decreasing with 0. 15 to 0 . 70 *** increasing distance from coast. 0. 27 to 0 . 53 t C . Higher elevations of Bolsa Chica VIII 7 0 . 3+ ** Mesa and Huntington Beach Mesa. 0 . 15 to 0 . 35 *** 0. 27+t * Esteva and Rosenblueth (1964) . ** Modified values based on Matthiesen, et al (1972) . *** Taken from Nuclear Reactors and Earthquakes , TID-7024 , United States Atomic Energy Commission, 1963 . t Neumann (1954) . N • FIGURE 3-5 • Amplification Factors Percent of Critical Acceleration Velocity • Damping Amplification Amplification 0 6. 4 4. 9 0. 5 5. 8 3. 6 • 1 5. 2 3. 2 2 4. 3 2 . 8 5 2. 6 2. 9 • 10 1. 5 1 . 3 20 1. 2 1 . 1 • After Newmark (1969) The use of the "response spectrum" in the design of buildings is a structural engineering matter and will not be considered further here. • • • • • 30 . pressure , the water within the soil will tend to flow upward which may turn the soil deposit into "quicksand" due to loss of shear strength. Flow to the ground surface may be manifested by ground . cracking and lurching. Lurching is inclastic deformation of the ground surface due to a loss of strength in underlying strata. Where soil thickness is variable or where the subsoil conditions are erratic, differential compaction of soil layers may occur resulting in differential settlement of the ground surface . The results of laboratory tests and investigations of liquefaction sites indicate that uniformly graded (i .e . , predominately one size such as beach sand) materials are more susceptible to lique- faction than well-graded materials and that for uniformly graded soils fine sands tend to liquefy more easily than do coarse sands, gravelly soils , silts , or clays . In addition, loose soil deposits will tend to liquefy more readily than denser deposits and shallower strata more than deeper strata. Further, intensity of ground shaking and duration of ground shaking play an important role. The longer the duration of strong shaking, the more likely that liquefaction may occur. Since the intensity and duration of ground shaking are somewhat proportional to the earthquake magnitude, liquefaction is more likely for moderate to strong earthquakes . Finally, the deeper the water table , the lower the liquefaction potential. Since field and laboratory investigations were not undertaken as part of this study, the depth to ground water was the major criteria in establishing liquefaction, lurching, and differential compaction potential for the City of Huntington Beach. Qualitative ratings of liquefaction, ground lurching, and different- ial compaction hazards for various areas within the City of Huntington Beach are tabulated below: Liquefaction, Ground Lurching and Differential Compaction Hazard Location High Low areas of poorly consol- idated recent alluvium within one mile+ of coast ; areas of saturated peat and organic soils overlying sandy deposits . Moderate to Low Inland areas of recent alluvium more than one mile from coast with hazard decreasing with increasing distance from coast. Low Marine Terraces located within the higher elevations of Bolsa Chica Mesa and Huntington Beach Mesa. Aft 31. It is emphasized that liquefaction potential depends upon many factors , in addition to groundwater level, factors such as soil type, relative density, and the intensity and duration of ground shaking. Each site needs to be evaluated individually. It is entirely possible that a detailed investigation of a site located in an area considered (in this general study) to have a high liquefaction potential may reveal low or no liquefaction potential and vice versa. • Areas prone to liquefaction and other seismicly induced hazards have been considered collectively and rated. The ratings are incorporated in the Geotechnical Land-Use Capability Map and Table in Section 4. 0 . 3. 4 Tsunamis and Seiches • Definitions Tsunamis (also called seismic sea waves or tidal waves) are sea waves believed to be generated by large submarine earthquakes , volcanic eruptions , and possibly large sub- marine landslides . Seiches are stationary oscillations of enclosed or partly enclosed bodies of water caused by landslides , sudden changes in atmospheric and wind pressure, or earthquakes . The "sloshing" of water in a pan that has been momentarily • tipped illustrates the mechanism of seiching. Only seismically induced seiches are considered herein. 3. 4. 1 Tsunamis (General) • All low-lying coastal areas of California are subject to the threat of tsunamis . The Presidio tide gage in San Francisco has recorded 19 tsunamis that ranged in height from less than six inches to over three feet during the period 1868 to 1968. The 1964 Alaska earthquake generated a tsunami that caused an estimated 12 million dollars in damages in more than a dozen California coastal towns and cities . It is reported (D'Arnall , 1973) that the 1964 Alaska earthquake produced a 114-foot high tidal wave" in the Huntington Harbor area. This was apparently not a breaking wave but a rapid rise in water level that resulted in some damage to anchored boats and in the flooding of the • Alamitos Bay area. Richter (1958) describes a great California tsunami that was generated by an earthquake in 1812 . It is reported that a 30-foot wave entered Refugio Harbor west of Santa Barbara and that a 50-foot wave may have struck Gaviota • 32 . about 20 miles west . Research into the sources of these reports by Marine Advisers , Inc. (1965) has shown that the reports are grossly exaggerated and based mainly on projec- tions from second-hand accounts . In 1927 it is reported • that a magnitude 7 . 4 earthquake produced a 5 to 7 foot high wave along the coast north of Point Arguello (Richter, 1958) . We did not find any confirmed records that a tsunami was generated by the 1933 Long Beach earthquake. • 3.4 . 2 Tsunami Hazard for Huntington Beach The tsunami hazard is considered to be VERY LOW for the higher elevations within Bolsa Chica Mesa and Huntington Beach Mesa and for other areas within the City limits located more than one mile from the coast. The low areas • within one mile of the coast are considered to have a LOW-TO-MODERATE tsunamic hazard depending on tidal condi- tions . This opinion is based on the following data: (a) Previous History • A search of available tsunami literature indicates that no known significant tsunamis have caused major damage to the Huntington Beach area within the period of recorded history of California. • (b) Distant Great Earthquakes Most tsunamis that have struck the California coast in the past have resulted from very distant earth- quakes , primarily in the Aleutians and other portions of the Circum-Pacific Belt of earthquake activity. • It is likely that these areas will continue to be the source of great earthquakes and tsunamis . Tsunamis undoubtedly have reached the coastal areas of Huntington Beach as a result of the 1960 Chile earth- quake and the 1964 Alaska earthquake. The eye- witness account described above indicates that the 1964 Alaska earthquake may have caused minor damage 41 in the Huntington Harbor area. Thus , the tsunami hazard associated with great distant earthquakes appears to be low-to-moderate , if high tide and the tsunami are coincident. (c) Local Offshore Event Current scientific opinions indicate that major California offshore faults are probably strike-slip faults (Emery, 1960) and that earthquakes generated on strike-slip faults are not likely to produce large- scale tsunamis (Wiegel , 1964) . Thus , the tsunami hazard associated with a local offshore event appears to be low. • 33. In summary, the potential for tsunami effects appears to be LOW-TO-MODERATE for Huntington Beach. ! As mentioned above , most tsunamis that have struck the California coast in the past have resulted from very distant earthquakes primarily in the Aleutians and other portions of the Circum-Pacific Belt of earthquake activity. Therefore, in most cases , there will be sufficient warning of approaching waves to permit the • evacuation of coastal areas . The warning will originate from the U. S . Coast and Geodetic Survey Observatory in Honolulu and will be transmitted to local law enforcement agencies by the California Disaster Office and the National Warning System (NAWAS) . The Tsunami Hazard Map (Figure 3-6) prepared by the California Division of Mines and Geology (1971) recommends that, in the Huntington Beach area, special caution be observed during a tsunami alert and that low coastal areas and public beaches be cleared if a flood tide and tsunamis • are likely to be coincident . 3. 4 . 3 Seiching The City of Huntington Beach boundaries encompass many • small ponds and Huntington Harbor which may be subject to earthquake induced seiching. A previously used method for evaluating seiching potential (Leighton-Yen, 1973) involved comparing the fundamental period of vibration of the body of water with the predominate period of ground shaking to determine the likelihood of resonance . • A crude estimate of the fundamental frequency can be made by the following formula: T = 2L n 1 2 i n(gd) (1) Where : T = fundamental period of oscillation in n seconds . L = length of water body, feet. • d = depth of water, feet. g = 32 . 2 ft/sec2 . n = integer corresponding to mode. • 34 . • :;. 4 *� ?: +► i >> • i. L- :: .... .. ....... ................ .................................................................................................................. is ........ ...........................:.. «::<...........:::::<:::«:;<:><:<;.:>::::::<:::<::>::>:<:>::>::> >::::::<:<:>::<:>::>::> ;>;>;:>;:::;>:;::>::>«.... ..... .. a .. . .. . ... .... »:;::::....... ... .. .iii :. ...... `....>: i:5ii :; > i:i:: ::--:::-:-5:::::. ... .:::::::.iii.'::: ii: :>: ::;:?;:::::> >::::ii:; i sr>[>::;::::::::::?c::'::;»»i»>............. ....... ...............::::: i:5:;:;;::5%:i: ..::.:..........: ....... .. �.\ :s::`:"::.::: ....:::::.:. ::.... ... .. .. :.::::.....::::.....::.... ,,. ::::"' \ •. :.:! NEW P • M AR zz::a 'r `::i • POomt- FfA� * POTENTIAL HARBOR DAMAGES F.i gure 377 AdWk TSUNAMI HAZARDS huntington beach planning department • 35 . • In addition, the maximum amplitude can be roughly esti- mated by the following formula: T d U h = n m m 2L (2) Where h = maximum amplitude , feet. m • U = maximum velocity across nodal line m ft/sec. Further refinements to the above equation (1) , which . applies to a constant depth rectangular tank, have been made for other shapes but their use is not justified in the present limited treatment of the problem. The follow- ing estimation of seiching height is only for establishing an order of magnitude for planning purposes . • Matthiesen' s (1972) curves for velocity versus distance indicate a peak velocity of 30 inches per second at the causative fault for a magnitude 6 . 6 earthquake. The minimum harbor width in Huntington Harbor is about 150 feet . This distance would also resemble the minimum width • of the smaller ponds . Larger widths would correspond to longer periods and are , therefore, not considered. The period of oscillation and maximum amplitudes for various water depths and modes of vibration are tabulated below for L = 150 feet and U = 2 . 5 feet per second. m • T , Seconds Maximum Wave Amplitude, Ft. d n feet n=1 n=2 n=3 n=1 n=2 n=3 5 24 12 8 1 0 . 5 0. 3 10 17 8 6 1 . 4 0 . 7 0 . 5 15 14 7 5 1 . 8 0 .9 0. 6 20 12 6 4 2 1 . 0 0. 7 Since the predominate period of earthquake ground shaking is not likely to exceed 1 second, it is unlikely that any portion of Huntington Harbor will oscillate in resonant response to ground shaking except for higher modes . The maximum wave amplitude associated with higher modes of oscillation will probably be less than 0 . 5 feet. So long as proper planning and design of adequate freeboard on waterfront structures are observed, seiching alone should not be a major constraint on development. Aft 36 . 3. 5 Peat and Organic Soil Deposits The approximate locations of previously mapped peat and organic soil deposits are shown in Figure 3- 7 Peat and Organic Soils . Additional unmapped deposits reportedly exist in the lower-lying portions of Huntington Beach. These deposits represent areas where long-term and large settlements may occur and where , during a major earthquake , potential liquefaction of subsoil and ground shaking may be antici- pated. A thorough geotechnical investigation should be performed for any development or structure to be located within or near these areas . 3. 6 Expansive Clays An expansive clay hazard potential map (Figure 3-8 Expansive Soil Distribution Map) has been prepared based upon the U. S. Department of Agriculture Soil Map (1919) . A qualitative rating system has been employed based upon the percent of clay size particles reported within the typical soil profiles of the upper six feet. • The hazard potential map indicates that the major deposits of clay having a MODERATE-TO-HIGH expansion potential are located within the inland areas of the northerly half of the City limits . The soils within this area are primarily clays , clay loams , and clay adobe with percentages of clay size particles ranging from about • 20 to 42 percent . Bolsa Chica Mesa and Huntington Beach Mesa contain loamy soils of the Ramona Series . The soils within the upper 12 to 24 inches exhibit percentages of clay size particles ranging from 6 to 11 percent , while the underlying soils have 20 to 27 percent clay size ♦ particles . On this basis , the upper one to two feet may be consid- ered as having LOW expansion potential , while the underlying soils have a MODERATE expansion potential . The major deposit of soils having LOW expansion potential is located southeasterly of Huntington Beach Mesa. The soils in this area are • predominantly silty fine sands and sandy silts with about 6 to 7 percent clay size particles . The southerly half of this area appears to contain sizeable areas of soils having MODERATE-TO-HIGH clay expansive potential . Included in the category of LOW expansion potential would, of course , be the coastal beach sands . • The tidal marsh areas have been assigned a VARIABLE expansive soil potential , because no one soil type predominates and the soils range from sands to clays . • • 37. 1 s T r n AM Z Z +�� Z � Z O� :I, lLlit� Wi- ;', iI it ... _ , �,`•A� 10 �l Z i Zo r. /f ... .� \ s,X -. ��)))}}�i) rill• i a /.. .:.:.. t / •. # P 5 � MAIN - - - � - � / y o ,00 R r✓+tf Op 4P T D . .. Z - Z Ll v Clt cn 'A a Fn u co Ilk tiF�q o`�a \� % PERCENTAGE OF CLAY CONTENT EM MODERATE TO HIGH 20%-42% 1 M LOW TO MODERATE 6%-27% � LOW 7%OR LESS VARIABLE REF. U.S.DEPT.OF AGRICULTURE � ® tPo� PP bpO SOIL MAP, �. e 10 .......... -- mM .. ........ HN '90111 ED sh P• § s���-� € � � ,� -:.1 � � �,s � � :, Trees �� €� w," 3 a .4 �_. ,: -. ...is _� ...- >>+e.:w..:... s ........::: ....-._ :€ bi, s � r:.€ .� L..... a€:I�:.o. �`g� :•:"P I�.'�r ....:::: � .. � "\ w ,. ,.,_.. .r,. .,.,` �:-.+. ....- � `•;tip _+.:... .,. ;��,>I .:..:, x: #.,. ,....:'� .,:,•- _ .,.-�' :-., .� �� �,, IN r, . 101,111 J SOURCE:LEIGHTON-YEN&ASSOC. 9-1-73 3- 8 j HUNTINGTON BEACH C4LIFORNIA EXPANSIVE SOIL DISTRIBUTION MAP 1 PLANNING DEPARTMENT Expansive clay soils can cause serious damage to lightly loaded structures , pavements , driveways , sidewalks, canal linings , etc. , # due to volumetric changes associated with increases or decreases in moisture content. Soil engineers can identify potentially expansive clay soils by means of laboratory tests . Therefore, it is important that private geotechnical consultants be employed to evaluate the problem and make proper design recommendations for individual structures . 3. 7 Beach Erosion Three geologic processes are continually operating in all beaches : erosion, transportation and deposition. When waves and .currents transport as much sediment into a particular beach as they transport out of the beach, a rough eT librium is attained between erosion and position and the beach is grossly stable. With one exception, the various beaches within the City limits of Huntington Beach appear to be stable . In common with most beaches in southern California, large seasonal variations in mass balance (erosion vs . sedimentation) occur, with erosion greatly predominating during the winter months because of more frequent storms , increased breaker height and a dominant southerly long shore current. This results in a general lowering and narrowing of the beaches in the winter and their corresponding buildup during the summer when the currents shift and storms are infrequent. Alan-made disturbances to the natural shoreline processes are very common along the southern California coastline and in some cases have been very detrimental from both an economic and scenic point- of-view. Reportedly (D'Arnall, 1973) , the stretch of beach in the vicinity of Surfside suffers from erosion due to the construction of the jetty at the entrance to Anaheim Bay. Apparently, annual replenish- ment of sand is required for this area. This is the only segment of beach known to be suffering from significant natural or man- caused beach erosion within the City limits . Although most beaches appear to have been stable since at least the early 1930's (D'Arnall, 1973; Air Phots , Appendix) , their long-range stability is dependent upon geologic factors whose analysis is beyond the scope of this investigation. i 3.8 Land Subsidence Land subsidence due to human activities in California has been recognized for many years . It is of concern because of the potential ! problems it can cause to structures and to the construction and 38. operation of drainage channels , sewers , pipelines , and water storage reservoirs (Barrows , 1973) . Subsidence related to man 's activities in California has been attributed to four different causes : (1) groundwater withdrawal , (2) oil and gas withdrawal , (3) hydrocompaction, and (4) peat oxidation (CDMG/Woodward-Lundgren, 1971) . Natural subsidence can result from sporadic, sudden faulting and slow area-wide (tectonic) deformation. Groundwater withdrawal has been identified as the most extensive type of man-caused subsidence in California (CDMG/Woodward-Lundgren, 1971) . Land subsidence of areas overlying oil fields along the Newport- Inglewood structural zone has been recognized for many years . An area (Miller, 1966) southwest of the Newport-Inglewood structural zone in the City of Huntington Beach has experienced some subsidence , reported to be as much in some locations as 5 . 1 feet between the years 1928 and 1965 (Barrows , 1973) . Recent information indicates the pattern of subsidence is complex, however, and does not appear to be directly related to oil field operations (Ledingham, 1973) . Tectonic subsidence and withdrawal of groundwater have been postulate as two possible causes of the subsidence. Very localized subsidence up to 14 feet is also reported to have occurred in scattered areas from Sunset to Newport Beaches just inland from the coast. Consoli- dation and possibly oxidation of peat layers caused by lower ground- water levels is the probable explanation (Bechtel , 1967) . Regardless of the cause , it does not appear that subsidence within the City limits has posed any serious problems of an economic or safety nature in the past (Day, 1973) . It is felt that with the current level of water injection into oil wells (300,000 to 400 ,000 barrels/day) (Day, 1973) , the chances of any future problems arising from land subsidence due to oil field operations are negligible. Little additional subsidence is expected from oxidation of peat deposits but this should be evaluated on a site by site basis . The potential problems associated with land subsidence are over-shadowed by other geotechnical concerns and would probably only become important in small localized areas of peat deposits . Land subsidence in Huntington Beach is indicated in Figure 3-9 . 3. 9 Groundwater Groundwater of adequate quantity and quality has been of importance in the Huntington Beach area since prehistoric times . Formerly, common "peat springs" were of probable importance to native Californians inhabiting the area prior to arrival of the white man. In more recent times , groundwater has been used extensively for domestic, agricultural and industrial purposes . 39 . i APPROXIMATE LOCATION oFti� SP 9�y.,: o * °o OF AREA HAVING EXPERIENCED ° sp Fob ryE ``� A VARIABLE AND COMPLEX PATTERN OF LAND SUBSIDENCE. r ° F "LAND SUBSDECE CAUFORNIA:'BY R EI MILLERI NSENGIiNE R- + ING GEOLOGY IN SOUTHERN CALIFORNIX ASSOCIATION OF ENGINEERING GEOLOGISTS, ►_�� �° s �� OCTOBER 1966. AND,`PRELIMINARY �Oo ° GEOLOGIC ENVIRONMENTAL MAP OF THE Its, o�r REATER LOS ANGLES AREA,WENTWO TH C. A�M.;Z ONY,J I.;AND Y BUCHANAN,J.M. U.S.A.E.C.T.I.D. 25363 25 ,E 1' 0 000 1970, NOT e°�s --dlHOE: EAFLOOR SUBSIDENCE NOT I 9 vis ♦ lP �' k \:PO � ir ViwS � \ dill x Tu Aj 9 % Jill t , n SOURCE:LEIGHTON-YEN&ASSOC. 9-1-73 3- 9 HUNTINGTON BEACH CALIFORNIA LAND SUBSIDENCE lop PLANNING DEPARTMENT c Groundwater of usable quantity and quality is confined to several well-known and well-defined subsurface zones known as "aquifers" . + These areally extensive aquifers are relatively thin, tabular bodies of coarse-grained sediments that readily allow the transmission of fresh water from inland areas toward the coast. These aquifers are separated from each other and the ground surface by layers of impermeable sediments which serve to confine the ground- water to the aquifer (and maintain its pressure) until tapped by a well or a geologic discontinuity. Fresh-water aquifers are confined to within several hundred feet of the ground surface in the area of Huntington Beach. Deeper bodies of groundwater are brackish and saline due to dissolved mineral content. 40 Depth to groundwater, whether saline or fresh, is of particular geotechnical significance in the Huntington Beach area for several reasons relating to foundation design and seismic ground response (see also, "Liquefaction, Ground Lurching, and Dynamic Compaction Hazards" , this report) . Generally, the groundwater table lies within ten feet of the surface for the first mile from the coast in i the areas of Santa Ana, Bolsa and Sunset Gaps . (DWR, 1966 ; Crandall, 1964) . It lies at an equivalent elevation beneath Huntington Beach and Bolsa Chica Mesas . Depth to the groundwater table gradually increases inland of the mile-wide coastal strip with increasing surface elevation. The various faults of the Newport-Inglewood structural zone, parti- cularly the North and South Branch Faults , act as permeability barriers with respect to the flow of groundwater (DWR, 1966 and 1968 ; Brown, 1973; Barrows , 1973) . This barrier effect has been of great benefit to the City, primarily because the intrusion of sea water into the fresh-water aquifers is limited and a relatively high groundwater table is maintained on the north side of the zone. Overdrafting of water wells and oil field operations have neverthe- less contributed significantly to the historic degradation of groundwater quality in the Iuntington Beach area (DWR, 1968) . Sea water intrusion was first noticed in the Santa Ana Gap in 1931 ; it became increasingly important during the 1940 's and by 1971, ground- water had been degraded in the Santa Ana Gap area for a distance of four miles from the coast (Brown, 1973 ; Bechtel , 1967) . Artificial recharge of aquifers , reduction in pumpage , and strict controls over disposal of industrial wastes and oil field brines have helped and will continue to help maintain groundwater quality within the City. Other, more sophisticated techniques are available as well (DWR, 1966) . • 40 . • In summary, it appears that groundwater problems are generally well- known and understood. The California Department of Water Resources • (DWR) is monitoring groundwater levels and quality throughout the state. The California Water Resources Control Board, in conjunction with Regional Water Quality Control Boards , is charged with enforcing water quality standards and correcting adverse conditions . • • • • • • • • • 41 . Section 4 geotechnical considerations • • • • SECTION 4. 0 GEOTECHNICAL CONSIDERATIONS FOR LAND USE PLANNING • 4. 1 Land Use Capability Analysis One of the significant results of this study was the development of a land use capability map which rates all land within the • planning area for possible geotechnical problems . In conjunction with the map a geotechnical land use capability table was developed which relates natural terrain type to characteristics and geotech- nical considerations . 4. 1 . 1 Geotechnical Land Use Capability Map The geologic problems identified in Section Three were used as the basis for developing the geotechnical land use capability map in Figure 4-1 . The map is intended to provide a guide for planning purposes . The values indicated are relative only and do not represent absolute values . The analysis that was used to develop the map included the following considerations : 1 . Fault rupture potential 2. Peat deposits 3. Liquefaction potential 4. Beach erosion 5. Tsunami Hazards Adft • 42. i : n 4 HIGH RISK—EXTENSIVE PROBLEMS ASP BF ®t O �o� 0 9C DIFFICULT OR IMPRATICAL TO k o �� ® y �� a s,P� Fo ties OVERCOME M HIGH RISK—MAJOR PROBLEMS BUT CONTROLLABLE THROUGH A.' ° O DESIGN AND/OR SETBACK '' c� PROVISIONAL RISK—MINOR TO MODERATE PROBLEMS tE NORMAL RISK—MINOR ' o �O , PROBLEMS �� THE GEOTECHNICAL PROBLEM RATING SCALE IS RELATIVE ONLY.THE I it .' �,a� _ �� ""- � �",':- MAP IS INTENDED TO BE A GENERAL GUIDE FOR PLANNING PURPOSES.THE MAP IS BASED ON THE FOLLOWING CONSIDERA- xt, s '.TIONS:FAULT RUPTURE RISK PEAT DEPOSITS,LIQUEFACTION .. \\�` " ,.�- ;'� I �; a „,;, -- -•s '•,pOTENTUIL,BEACH EROSION AND TSUNAMI HAZARD.SPECIFIC- `'� 3 ;»t �,"21€11 '*✓ \ ,-\ ALLY EXCLUDED FROM CONSIDERATION WERE GROUND O •. .a, - :. ,aV . ., } an.. .:..� SHAKING EXPANSIVE SOILS AREAL L SUBSIDENCE, 'h,• ..�\,. A AND 'GROUNDWATER PROBLEMS AND FLOOD HAZARDS. .�. �` �T � y-� E �, ➢:? a Sill ? ' p .. ,J ,,fig y 't`,` .^s '.n.; �' 1 �. ,, •k '- ", i Ba yr' �'i`s x, �� ✓r+� ,'� r �itJf,'.p II ;;_�\ti :r'.. � Ali€E x�� � :..:��;. �:. y I t , ♦, x.< ..; ��,,•.-: '^-.,-.:n,; "���'1 $ ^.;��•.. a ` � �'�b.�:-_ "il � �r";y i ���' ��, .ate. ,w a.. J ^w IN' 1Z IT i Nt :8 SOURCE:LEIGHTON-YEN 8 ASSOC. 9-1-73 4 - 1 HUNTINGTON BEACH C4LIFORNIA GEOTECHNICAL LAND USE CAPABILITY MAP PLANNING DEPARTMENT Specifically excluded from this analysis were : 1 . Earthquake shaking 2. Expansive soils 3. Areal land subsidence 4 . Groundwater problems The analysis was based upon an accummulation of geologic problems and relative degrees of severity. Based upon this , four values were determined: • 1 . Nominal Risk - Areas that display the least problems from a geotechnical point of view. Problems when they exist are minor or on a micro-scale. Areas in this category are the Huntington Beach and Bolsa Chica Mesas and those areas of the alluvial flood plain that are farthest from the coastline. 2 . Provisional Risk - Moderate geologic problems are prevelant in these areas . Usually these areas have problems that are related to soil conditions , such • as peat or alluvial soils . The provisional risk areas are in the various portions of recent alluvium deposits as indicated in Figure 1-3 Geologic Condi- tions . 3 . High Risk - Areas that have potential major geologic • problems but are controllable through design or locational criteria. Areas delineated for this risk have either one geologic problem of high risk, such as an active fault or a culmination of problems such as soil conditions , tsunami hazard, etc. Most of the high risk areas are dominated by either high • liquefaction potential (near the coastline) or active fault location. 4. High Risk - Extensive problems that are difficult or impractical to overcome . Most of the areas in this category are the fault zones that are most likely to experience surface rupture (Refer to Figure 3-1 Fault Map) . Areas that are subject to a combination of other factors may also be indicated in this category. These occur in the alluvium or tidal marsh areas . • 4. 1 . 2 Geotechnical Land Use Capability Table This table (Figure 4-2) is intended to be used with the geotechnical land use capability map and the geologic conditions map. It describes the terrain type or geologic hazard area in terms of its natural terrain characteris- tics and geotechnical considerations . • 43. FIGURE 4-? IiUNTINGTON BEACH - GEOTECHNICAL LAND USE CAPABILITY TABLE NATURAL TERRAIN TYPE NATURAL TERRAIN GEOTECHNICAL OR HAZARD AREA CHARACTERISTICS CONSIDERATIONS • BEACH Elongate strip of High energy environment; coastline immediat- subject to rapid storm ely adjacent to and seasonal (winter) Pacific Ocean. erosion. Has been Width and cross- grossly stable for many • sectional profile years . Highly susceptible seasonally variable , .to man-caused disturbances but generally gently that interfere with natural , sloping and extend- shoreline processes . ` ing up to 1000 ' + Highly permeable ; saline inland. - Terminates groundwater at shallow linland against depth. ' mesas , floodplain land tidal marshes ; ' gentle, regular topography continuesi offshore for several # ' miles . Underlain by , : unconsolidated sands . TIDAL MARSH Flat-lying land at High ground water level, (BOLSA & SUNSET for near sea-level. subject to tidal fluctua- GAPS) lIrregular tidal tions . High liquefaction channels , swampy ?potential. Fresh water , ground; character- Caquifers at depth subject . istic salt-water to potential water quality ! loving vegetation. (degradation. Subject to ( Underlain by mud (flooding locally expansive • ; and organic-rich soils . ; muck over coarser- grained sediments . Poorly defined land- ward boundary Jagainst flood plain ' terrain. FLOODPLAIN iUniform, gently Subject to flooding. High (SANTA ANA GAP) + seaward-sloping water table and liquefaction terrain along potential near coast. present course of Important fresh water Santa Ana River as aquifers at depth subject to well as landward of potential water quality Bolsa Gap (former degradation. Scattered Santa Ana River thick peat deposits of high course) and Sunset liquefaction potential and Gap. Underlain by insufficient load-bearing variable unconsoli- capacity. Locally expansive dated sediments . soils . • 44 . IIUNTINGTON BEACH - GEOTECHNICAL LAND USE CAPABILITY TABLE (CONTINUED) NATURAL TERRAIN TYPE NATURAL TERRAIN GEOTECHNICAL i OR HAZARD AREA CHARACTERISTICS CONSIDERATIONS MESA Relatively flat Relatively minor geotechnical (HUNTINGTON BEACH erosional surfaces , constraints outside of fault $ BOLSA CHICA MESAS) ;elevated 25 ' to 50 ' hazard areas . Generally low �• I'above surrounding to moderate expansive soils . floodplain and tidallConsidering flood hazard and 'marsh, commonly fall other constraints not bounded by pronounc- lincluded in LAND USE CAPABILITY -ed scarp . Surfaces (MAP , this terrain unit is the well-defined near Imost suitable for high intensity coast, but merge development and critical • inland with flood- facilities . Contains -plain. Major topo- commercial quantities of sand graphic irregular- and gravel. ities of mesa jsurfaces related • jto faulting within (Newport-Inglewood structural zone see below) . FAULT OR `General trend of Zones surrounding faults FAULT ZONE Newport-Inglewood (400 ' wide) arbitrary and • (NEWPORT-INGLEWOOD structural zone in intended to indicate STRUCTURAL .ZONE) Los Angeles area imprecision of fault `coastal plain marked location due to limitations by a line of low, lof data as well as to contain domal-shaped hills . great majority of any short • North and south branch faults. branch faults topo- graphically expres- Figure 3-1 indicates faults sed on Huntington believed to be active. No Beach Mesa by a structure for human occupancy series of minor should be located over an hills and depres- active fault. The area ' sions . Faults well- within 50 ' of an active expressed by a 25 ' fault is assumed to be high scarp across underlain by active branches 'Bolsa Chica Mesa. unless and until proven otherwise. Over fault zones believed to be potentially active no habitable structure should be built. Detailed studies required. • • 45 . • 4 . 2 Recommended Geologic Considerations for Land Use Planning Based upon the identification and analysis of geologic problems and a the land use capability analysis the firm of Leighton-Yen and Associates reached the following conclusions : 4 . 2 . 1 Seismicity • The City of Iuntington Beach is located in a seismically active area. It has experienced numerous earthquakes from both distant and local sources and will continue to do so in the future . Within the next 100 years , seismic events of major importance to the City of Huntington Beach are most likely to originate on the Newport-Inglewood and San Andreas Fault Zones . 4. 2 . 2 Adequacy of Existing Data Existing earth science and seismic data are considered adequate to prepare a preliminary assessment of the type and magnitude of seismic hazards . Significant limitations exist in the state-of-the-art of determining the magnitude of potential ground shaking, tsunami and seiche phenomena. For example, most records • gathered to date on ground shaking were obtained at a distance greater than 20 miles from the causative fault. Hence , near-fault ground motion is not well-known or understood, particularly for larger earthquakes - a fact of significance for Huntington Beach, lying as it does directly over an active fault zone. Significant advances • in the theoretical state-of-the-art of near-fault ground motion are considered imminent, however, and will be of great importance to the City of Huntington Beach. Although information was adequate to determine which of the faults in the City should be considered active, the i! information is inadequate to locate these or other faults with sufficient precision for detailed zoning purposes , although there is a high probability the faults lie within the shaded areas shown on the fault map . The existence of active branch or active secondary faults is undetermined. Detailed geologic investigations involv- ing subsurface exploration is required to more precisely define fault location and activity. Conclusions that follow are based on existing data and are subject to modification as more knowledge is gained through specific • 46 . detailed studies . In this regard, it is emphasized that the Fault, Geologic and Geotechnical Land-Use Capability • Maps should be regarded as dynamic documents subject to continual revision as more and better information becomes available to the City. 4. 2 . 3 Fault Displacement The probability of surface rupture occurring within the next 100 years on the North Branch, Bolsa-Fairview and South Branch Faults is relatively low overall but in the area within and to the nort west of Bolsa Chica Lagoon the probability of rupture is considered to be higher. The North Branch Fault (also known as the High School Fault) is considered the main active fault within the City and the fault most likely to be associated with future surface rupture as well as having the greatest amount of surface displacement. The possibility exists that surface rupture could also occur on any of the other faults shown on the Fault and Geotechnical Land-Use Capability Maps . These faults , shown in orange in the Geotechnical Land-Use Capability Map are considered potentially active . Based on available information it is felt that surface displacement , should it occur on any of the faults within the City, will be on the order of a few inches , although additional studies may indicate the potential for greater movement . 4. 2 . 4 Fault Hazards and Land Use Earth science information is sufficient to indicate that the zones surrounding the faults as shown on the Fault and Geotechnical Land-Use Capability Maps are areas of substantially higher than average seismic risk. It is recommended that the public be advised of this fact and that consideration be given to the designation of these areas as Geologic Hazard Zones as defined in the Alquist- Priolo Geologic Hazards Zone Act (Chapter 7. 5, Division 2, Public Resources Code, State of California) , and subject to additional detailed studies as discussed under Ade5uacy of Existing Data that would be needed to better define and locate the faults . • 47. The designation of some , or all , of the fault hazard zones (meant here to be the zone surrounding an active or poten- tially active fault) as Geologic Hazard Zones would have to be based on an agreement with the State Geologist and would require the accomplishment of certain special studies based on the criteria, as specified in the Draft Statement of August 24, 1973 issued by the State Mining and Geology Board regarding the Alquist-Priolo Act. Even if, on the basis of additional geologic studies , it is determined to designate some, or all , of the fault hazard zones as Geologic Hazard Zones , it is not antici- pated that unacceptable risk levels will be found to exist with respect to existing single family residences and other low occupancy structures . It is possible , however, that a long-range abatement plan pointed towards reduced levels of occupancy or alternative land uses within all or certain portions of the fault hazard zones will be found to be a feasible solution to the fault displacement hazard. • Sites of schools , high occupancy structures and other critical facilities currently existing within the North Branch, Bolsa-Fairview and South Branch fault hazard zones should be subjected to detailed geologic-fault investiga- tions as soon as possible. There is a reasonable possibil- ity that one or more of these structures will be found to be existing under conditions of unacceptable fault displace- ment risk. 4 . 2 . 5 Ground Shaking The present state-of-the-art does not permit reliable evaluation of the intensity of ground shaking near the causative fault . However, to provide an interim basis for establishing minimum aseismic design, an attempt has been made to correlate ground motion parameters , namely • peak velocity and acceleration, to reasonable estimates of Modified Mercalli Intensity based upon the 1933 Long Beach earthquake. This data is presented in Table V. Values to be used in design will depend upon local soil conditions and the importance factor of the structure . It is expected that as additional records of ground 1 motion near the causative fault become available in the future, a narrower range of peak ground acceleration can be established. • • 48 . • 4. 2 . 6 Liquefaction A ground stability analysis should be required as part of obtaining a building permit for developments located within the areas designated as having MODERATE and HIGH liquefaction potential . Such an analysis should also be submitted in the event that shallow groundwater (20 feet or less) is encountered in other areas underlain by recent or older alluvial deposits . This requirement would ensure that professional geotechnical consideration is given to the potential problems of liquefaction, ground lurching and differential compaction. The scope of the investigation might range from a professional opinion based upon local experience, to field and laboratory studies as determined by the professional consultant and the size and importance of the project. 4. 2 . 7 Tsunamis and Seiches The tsunami hazard is considered to be VERY LOW for the higher elevations within Bolsa Chica Mesa and Huntington Beach Mesa and for other areas within the City limits located more than one mile from the coast. The low areas within one mile of the coast are considered to have a LOW-TO-MODERATE tsunamic hazard depending on tidal condi- tions. • Seismically induced seiching is expected to be limited to Huntington Harbor and the various small ponds located throughout the City. Our analysis indicates that it is highly unlikely that any of these ponds or any portions of Huntington Harbor will oscillate in resonant response to ground shaking except for higher modes- of oscillation. The maximum wave amplitude associated with higher modes of oscillation will probably be less than 0 . 5 feet. Therefore seismically induced seiching should not represent a major constraint to development within the City provided suffi- cient setback and/or freeboard are incorporated into the design of waterfront structures . 4 . 2 . 8 Peat and Organic Soil Deposits . The approximate locations of major deposits of peat and organic soil have been identified. It is recommended that the peat map be revised and updated by the City as additional information becomes available from other sources e. g. , consultant 's soil reports , Orange County Planning Department. These deposits represent areas where long- term and large settlements may occur and where, during a major earthquake, potential liquefaction of subsoil and Adft 49 . ground shaking may be anticipated. A thorough geotech- nical investigation should be performed for any develop- ment or structure to be located within or near these areas . 4 . 2 . 9 Expansive Soils Expansive clay soils which are widespread throughout the City can cause serious damage to lightly loaded structures , pavements , driveways , sidewalks , canal linings , etc. , due to volumetric changes associated with increases or decrease in moisture content . Soil engineers can identify potential- ly expansive clay soils by means of laboratory tests . Therefore , it is important that private geotechnical consultants be employed to evaluate the problem and make proper design recommendations for individual structures . 4. 2. 10 Slope Stability Slope stability problems are not considered to be a significant constraint or planning concern within the City. In the event of strong ground shaking, there is a low but finite possibility that a number of relatively small landslides could occur in the areas of steeper slopes bordering the mesas . 4. 2 . 11 Subsidence Subsidence due to man-caused activities has been recognized within the City of Huntington Beach. No damage or safety hazard is known to be associated with this phenomenon to date. Reportedly, there is no indication that subsidence, in connection with secondary oil recovery techniques in the Huntington Beach Oil Field, has reactivated any faults i� or stimulated increased levels of seismicity. Neither are these effects anticipated to occur in the future . 4. 2 . 12 Upgrading the Technical Data Base The need for detailed geologic investigations in the fault hazard zones has been previously discussed. The City should ensure that the active faults are investigated in each of the differing surficial earth units and that the information is gained in enough detail and depth to permit extrapolation throughout the City. • • 50 . Geophysicists at the University of Southern California, in cooperation with oil companies and municipalities , have established a seismic monitoring network across the Newport-Inglewood structural zone. It is centered in the Long Beach and Inglewood areas and has the potential of providing much useful information for land planners . It is suggested that the City of Huntington Beach inves- tigate the possibility of entering the network on a cooperative basis . 4. 2 . 13 Updating and Periodic Maintenance of the Seismic Safety Element This inventory of seismic and other geotechnical consider- ations has of necessity been both broad and generalized. The element should be updated as significant new geotech- nical information becomes available , as the State-of-the- Art with regard to seismic considerations advances , and as social values and definitions of "acceptable risk" change. • _1R...jF • • • • 51 . section 5 • seismic - safety element • • • SECTION 5. 0 THE SEISMIC - SAFETY ELEMENT As discussed below, the State requires each city and county to develop a Seismic Element and a Safety Element in the interest • of public health, safety, and welfare. The required content of these mandated General Plan elements overlaps to a considerable degree, however; and in the interests of a comprehensive approach to the problem of community security, they will be combined into a joint Seismic-Safety Element for the City. a 5. 1 Safety Legislation :5. 1. 1 Seismic Safety Element • In 1971, Section 65302 (_f)_ of the California Government Code made Seismic Safety the sixth mandated element of the General Plan and required "an identification and appraisal of seismic hazards such as susceptibility to surface ruptures from faulting, to ground shaking, to ground failures, or to effects of seismically induced waves such as tsunamis and seiches". Additionally, the law specifies that the element include "an appraisal of mudslides, landslides, and slope stability as necessary geologic hazards that must be considered simultaneously with other hazards such as possible surface ruptures from faulting, ground shaking, ground failure and seismically induced waves". S 52 5 . 1. 2 Public Safety Element Also in 1971, a Safety Element "for protection of commu- nity from fires and geologic hazards" was added to the General Plan by Section 65302. 1 of the California Government Code. The law stipulates that the element shall include "features necessary for such protection as evacuation routes, peak load water supply requirements, minimum road widths, clearances around structures, and geologic hazard mapping in areas of known geologic hazards". 5. 1. 3 Alquist - Priolo Geologic Hazards Zones Act Probably the most significant legislation relating land use with seismic safety, this act orders the State Geologist to prepare maps by December 31, 1973, showing "special studies zones" along active earthquake faults which will be provided to all cities and counties having jurisdiction over land within these zones. Additionally the statute requires the State Mining and Geology Board to develop criteria for evaluating development within these zones. The act further stipulates that every structure intended for human occupancy must get approval from the appropriate city or county; and approval cannot be granted if the local government finds that aan'undue hazard" would be created. CThe act specifically 40 states that cities and counties may adopt stricter policies and criteria than those established by the State. ) The special studies zones to be mapped include "all potentially and recently active traces of the San Andreas, Calaveras, Hayward, and San Jacinto Faults, and such • other faults or segments thereof, as he deems sufficiently active and well-defined as to constitute a potential hazard to structures from surface faulting or fault creep" . Though Huntington Beach is not presently included in any • "special studies zone", additional zones may be delineated in the future which encompass the Newport-Inglewood Fault through the City. At such time the following criteria would be enforced for any development project within the zone boundaries : A. No structure for human occupancy shall be permitted to be placed across the trace of an active fault. Furthermore, the area within fifty C5 01 feet of an active fault shall be assumed to be underlain by active branches of that fault unless and until proven otherwise by an appropriate geologic investi- gation and submission of a report by a geologist registered in the State of California. i * 53 B. Applications for all real estate developments and structures for human occupancy shall be accompanied by a geologic report prepared by a geologist regis- tered in the State of California, and directed to the problem of potential surface fault displacement through the site, unless such studies are waived pursuant to Section 2623. C. One Cl) copy of all such geologic reports shall be placed on open file with the State Geologist. D. Requirements for geologic reports may be satisfied for a single 1 or 2 family residence if, in the judgment of technically qualified City and County a personnel, sufficient information is available from previous studies in the same area. E. Technically qualified personnel within or retained by each City or County must evaluate the geologic and engineering reports required herein and advise the body having jurisdiction and authority. F. Cities and Counties may establish policies and criteria which are more restrictive than those established herein. In particular, the Board believes that comprehensive geologic and engineering studies should be required for any major development Ce.g. high-rise buildings), or "essential" structure (e.g. hospitalsl whether or not it is located within a special studies zone. 5.1. 4 Other Legislation Seismic design requirements were first incorporated into the Uniform Building Code after the disastrous 1933 Long Beach earthquake, and some important refinements were suggested after the February 9 , 1971 San Fernando earthquake. Of particular significance are the following: School Construction CSB 4791 - requires site evaluation of the probability for eart quake damage from causes such as sudden or slow slippage along a fault within a site, landsliding, differential compaction, ground cracking, + liquefaction, tsunamis and seiche waves. Section 15002. 1 of the Education Code was amended by SB 689 so that "No school building shall be constructed or situated on the trace of an active geological fault. . .active Is defined as one along which surface rupture can be reasonahly S expected to occur within the life of the building". (Adopted 1971) 54 Hospital Construction CSB 519) - requires that engineering and geologic data be reviewed by a civil engineer, struc- tural engineer, certified engineering geologist and licensed architect. . .makes it a felony to knowingly make false statements in reports. . .establishes State earthquake resistance standards on new construction, reconstruction or alterations. (Adopted 1972) Subdivision Map Act CSB 158 Rodday - modifies the sub- division requirements of the Rea Estate Commission to require detailed geologic report for tentative tracts of more than five parcels. As proposed, geologic reports will be required where geologic hazards are known or when slopes are steeper than 5:1 ratio. (Adopted 19721 5.2 CIR Guidelines Tiie California Council on Intergovernmental Relations offers addi- tional definition to state law in its General Plan guidelines published in September, 1973. CIR suggests that the Seismic Element include: A. A general policy statement that: 1. Recognizes seismic hazards and their possible effect on the community. 2. Identifies general goals for reducing seismic risk. 3. Specifies the level or nature of acceptable risk to life and property (see safety element guidelines for the concept of "acceptable risk") . 4. Specifies seismic safety objectives for land use. 5. Specifies objectives for reducing seismic hazard as related to existing and new structures. B. Identification, delineation and evaluation of natural seismic hazards. a C. Consideration of existing structural hazards. Generally, existing substandard structures of all kinds (including substandard dams and public utility facilitie.sl pose the greatest hazard to a community. t D. Evaluation of disaster planning program. For near-term earthquakes, the most immediately useful thing that a community can do is to plan and prepare to respond to and recover from an earthquake as quickly and effectively as possible, given the existing condition of the area. The. seismic safety element can provide guidance in disaster planning. ACEM 55 • E. Determination of specific land use standards related to level of hazard and risk. • The guidelines also present a suggested methodology: A. Initial organization 1. Focus on formulating and adopting interim policy based A on very general evaluation of earth science information readily available. 2. Evaluate adequacy of existing information in relation to the identified range and severity of problems. 3. Define specific nature and magnitude of work program needed to complete the element in a second stage. • B. Identification of natural seismic hazards 1. General structural geology and geologic history. 2. Location of all active or potentially active faults, with evaluation regarding past displacement and probability of • future movement. 3. Evaluation of slope stability, soils subject to liquefac- tion and differential subsidence. 4. Assessment of potential for the occurrence and severity of damaging ground shaking and amplifying effects of unconsolidated materials. • 5. Identification of areas subject to seiches and tsunamis. 6. Maps identifying location of the above characteristics. C. Identification and evaluation of present land use and circula- tion patterns should be recognized in the formulation of seismic safety-land use policies. • D. Identification and evaluation of structural hazards relating structural characteristics, type of occupancy and geologic characteristics in order to formulate policies and programs to reduce structural hazard. • E. Formulation of seismic safety policies and recommendations. F. Formulation of an implementation program. CIR guidelines outline a Safety Element as containing: I• A. General policy statement that: 1. Recognizes safety hazards. 2. Identifies goals for reducing hazards. 3. Specifies the level of acceptable risk. • 4. Specifies objectives to be attained in reducing safety hazards as related to existing and new structures. I -1fi.J1 • 56 • 5. Sets priorities for the abatement of safety hazards, recognizing the variable frequency and occurrence of • hazardous events. B. A map showing the location and extent of known geologic hazards. C. Standards and general criteria for land use and circulation relating to: • 1. Fire prevention and control 2. Geologic hazards D. Consideration may be given to the crime prevention aspects of land use development such as planning for "defensible space". • Additionally, a sample methodology is presented: Methodology A. Identification, mapping and evaluation of existing and potential • hazards, both as to severity and frequency of occurrence. Analysis of hazardous land use relationships. B. With maximum citizen input "acceptable risk" should be deter- mined. In making this determination, it should be kept in mind that any attempt to develop the appropriate planning • response to potential hazard involves a judgment, either explicit or implicit, of how much risk is acceptable. There is no such thing as a perfectly hazard-free environment. Natural and man-made hazards of some kind and degree are always present. However, efforts can be productively undertaken to try to mitigate the consequences of known hazards. • In the context of the Safety Element, the problem of risk is one of public policy and the appropriate allocation of public resources to mitigate hazards. The central question is, "how safe is safe enough?" The planner' s responsibility is to provide a framework in which a communitywide, as opposed to • an individual, response to the question can be meaningful. The first of several essential steps is the recognition of the presence of a hazard. Much of the planning of the past has proceeded without enough knowledge of the natural forces at play in a given area. • Once a problem has been recognized, considerable effort is required to evaluate its likely severity, frequency, and the characteristics of the area involved. This step should take into account the benefit/cost ratio of reducing hazard, acknowledging the intangibles involved, and comparing it with.- that of other projects. The factors of voluntary and involun- tary exposure to risk must be considered in reaching a decision. • 57 • C. Define nature and magnitude of effort required to correct or mitigate hazards. • D. Define general nature of regulations and programs needed to prevent or mitigate the effects of hazards in the developed and natural environments. E. Exchange information and advice with fire, police and public • works departments, other agencies, and specialty personnel in the formulation of the element. As required by state law, all elements are to be completed one year after publication of CIR guidelines; that is, September, 1974. • 5. 3 Methodology This Geotechnical Inputs document is a background report for the Seismic E ement and only a beginning step in development of a comprehensive joint Seismic-Safety Element of the General Plan. • The following paragraphs briefly outline the approach adopted to insure that the final seismic-safety program is a realistic and workable one that effectively minimizes risk to life and property. 5. 3. 1 Interdisciplinary Approach_ • The subject of seismic and public safety is a highly complicated one. In like manner, development of comprehensive seismic and safety plans requires not only the skills of the planner but many technical specialists, as well. To insure that the Element is prepared with an • in-depth understanding of the natural hazards that confront the community, the City will rely on a five- member interdisciplinary team to supervise all safety planning activities. Representing Planning, Building and Safety, Public Works, Fire, and Civil Defense Departments, the team will consist of two registered • civil engineers, a fire marshall, a civil defense coordinator, and a planner. Coordinated by the Planning Department, the team will be responsible for reviewing and/or conducting the research, site investigation, inspection, plan formulation and ordinance proposals necessary to complete the Seismic-Safety Element. • 5. 3.2 Background Studies In addition to general research activities, two special • studies will be conducted as background reports for the Seismic-Safety Element. This Geotechnical Inputs AMnA! HJP 58 • document is one such report; the other is a Flood Plain Study which will examine the nature and potential of • flooding in the Santa Ana River Flood Plain, identify existing and proposed control measures, and identify land use hazards. These two studies will form the data base for plan formulation. • 5.3. 3 The Element Phase Two will consist of formulating the joint Seismic- Safety Element in conformance with General Plan law (Section 5. 1) and CIR guidelines (Section 5 .2) . Finally, the team will develop long-range and short-term implemen- tation programs designed to minimize risk, upgrade hazardous conditions, and insure proper development in the future. Some implementation techniques to be considered include: inspection programs, renewal, seismic hazard management zones, disaster contingency plans, etc. • • • a • • • 59 section b appendix APPENDIX A CITY OF HUNTINGTON BEACH SEISMIC SAFETY ELEMENT GLOSSARY OF TERMS ALLUVIUM A general term for all sediment such as sand and gravel deposited by streams; (adjective: alluvial) . ANTICLINE Bedrock that has been folded in such a way that the beds (strata) are convex upward. May be less than an inch or several miles in extent. BEDROCK Firm or coherent rock material that underlies the soil or "overburden" ; divided geologically into 3 classes: igneous, sedimentary, and metamorphic. DEFORMATION A change in the form of a body of rock by mechanical means, i.e. , folding or faulting. DIFFERENTIAL COMPACTION Non-uniform consolidation of loose, saturated soils due to earthquake induced ground shaking. EARTHQUAKE Ground motion resultant from the relative movement of two blocks of the earth's crust along a fracture surface (i.e. , fault) . 40 See FAULT, SURFACE RUPTURE. EPICENTER The point on the earth's surface directly over where the focus or point of origin of the quake occurred. • FAULT A fracture or fracture zone along which there has been movement (slippage) of two sides relative to one another and parallel to the fracture. Based on seismic activity, faults can be divided • into three categories: 60 (1) active faults can be associated with historic seismic activity, • (2) potentially active faults have not been associated with historic seismic activity, but give evidence of geologically recent activity, and (3) inactive faults do not show evidence of activity within approximately the last one million years (i.e. , the beginning of the Pleistocene) . FORMATION To a geologist, this is a rock body which can be recognized, named and mapped, e.g. , San Pedro Formation, etc. GEOTECHNICAL Pertaining to geologic-soils engineering studies, features, conditions or events. GROUND RUPTURE See SURFACE RUPTURE. • HYPCENTER In an earthquake, the point of initial rock rupture or slippage; always a point within the earth. IGNEOUS The class of rocks formed by cooling and crystallization from a molten state; includes volcanic erupted molten rock and subsurface intruded molten rock. INTENSITY 40 A qualitative measure of the destructiveness of an earthquake; a number scale, e.g. , Mercalli. LIQUEFACTION The sudden, large decrease of shearing resistance of a cohesionless soil caused by collapse of the soil structure, produced by seismic shaking or small shear strains, associated with sudden but temporary increase of water pressure in the soil voids. • 61 i LURCHING Inelastic deformation of the ground surface due to a loss of strength in underlying strata due to earthquake induced ground shaking. MAGNITUDE A quantitative measure of the total energy release of a quake; a logarithmic number scale, e.g. , Richter. RECURRENCE INTERVAL The average length of time between earthquake events of a specified magnitude. SATURATED A rock or soil is saturated with respect to water if all its voids are filled with water. • SEDIMENTARY ROCK The class of rocks made up of transported and deposited rock and mineral particles (sediment) and of chemical substances derived from weathering. • SEICHING Stationary oscillations of enclosed or partly enclosed bodies of water caused by an earthquake, landslide, or a sudden change in atmospheric and wind pressure. i SEISMIC Of or related to earthquake shaking. SETTLEMENT a The downward movement of a soil or of the structure which it supports, resulting from a reduction in the voids in the underlying strata. SILTSTONE A sedimentary rock of cemented, fine-grained particles intermediate in size between sand and clay (silt) . STRATIFICATION ♦ A structure of sedimentary rocks produced by deposition in layers (beds) . • 62 • SUBSIDENCE The relatively slow, gradual sinking of a large area in a vertical direction with little or no horizontal movement. SURFACE RUPTURE During an earthquake, the permanent displacement (or offset) of the earth's surface along a fault plane. Ground breakage at the earth's surface. TECTONIC Pertaining to rock structure resulting from deformation of the earth's crust. TSUNAMI Seismic sea wave produced by a submarine earthquake or volcanic eruption. • • • • • • 63 APPENDIX B SELECTED REFERENCES CITY OF HUNTINGTON BEACH Albee, A. L. $ Smith, J. L. , 1966, Earthquake characteristics and fault activity : in Engineering Geology of southern California; Association of Engineering Geologists . Andreasen, G. E. , et al , 1964, Aeromagnetic map of the Long Beach- Santa Ana area, Los Angeles and Orange County, California: U. S. Geol . Survey Geophysical Investigation Map GP464. Bandy, 0. L. $ Marincovich, L. Jr. , 1973, Rates of late Cenozoic uplift, Baldwin Hills , Los Angeles , California: Science , vol. 181, No. 4100 . Barrows, A. G. , 1973 , Earthquakes along the Newport-Inglewood struc- tural zone : in California Geology, vol . 26, No . 3. Denioff, Hugo , 1938, The determination of the extent of faulting with application to the Long Beach earthquake: Seis . Soc. of America Bull. vol . 28, no. 2 . • Brown, Glenn A. $ Associates , 1971, Preliminary hydrogeologic investigation of Bolsa Gap : for Signal Properties , Inc. California Dept. of Water Resources , 1966, Santa Ana Gap salinity barrier, Orange County: DWR Bull. 147-1 . , 1964, Crustal strain and fault movement investigation : DWR Bull. 116-2 . 1968, Sea water intrusion Bolsa - Sunset area, Orange County: DWR Bull. No. 63-2 . • 1967, Progress report on groundwater geology of the coastal plain of Orange County. California Division of Mines and Geology, 1962, Long Beach map sheet: 1 : 250 ,000. • 1954, Geology of southern California: CDMG Bull. 170, Chapter II and map sheets 32, 34. , 1972 , Geologic map of California, southern half: (open file) , compiled by C. W. Jennings , 1 : 750,000. • 64 1943, Geologic formations and economic development of the oil and gas fields of California : CDMG Bull . 118. California Division of Mines and Geology, Woodward-Lundgren and Associates , 1971 , Urban geology master plan for California; a method for setting priorities : California Division of Mines and Geology. California Division of Oil and Gas , 1970 , Production statistics , 1970 : California oil fields , vol . 56, no. 2 . Carls , J. M. , 1949, Recent developments in the tar sands of the Townlot area, Huntington Beach oil field: D.O. G. vol. 35, #1. Carriel , James T. , 1942 , Huntington Beach oil field; oil field portions : D.O. G. vol . 28, # 1 . Coast and Geodetic Survey, n .d. Tsunami - the story of the seismic sea wave warning system: U. S. Department of Commerce. Corwin, C. H. , 1946, West Newport oil field: D.O. G. vol. 32, # 2. Cox, D. C. , 1964 , Tsunami forecasting: Technical report prepared for Office of Naval Research under contract number NONR-3748 (03) , Hawaii Institute of Geophysics , University of Hawaii. Crandall , Leroy, $ Associates , 1964 , Report of preliminary soil investigation proposed development , Pacific Coast Highway and Warner Avenue, Orange County, California: for Bolsa Properties . D'Arnall, Captain D. G. , 1973, Huntington Beach Department of Harbors a and Beaches , personal communication. Emery, K. 0. , 1960 , The sea off southern California: John Wiley & Sons , Inc. , New York, 366p. Esteva, L. and Rosenblueth, E . , 1964, Espectros de temblores a distancias moderadas y grades : Boletin, Sociedad Mexicana de Ingenieria Sismica, V. 2 , No. 1 . Fairbridge , R. W. , 1968, Beach erosion and coastal protection: Coastal classification in the Encyclopedia of Geomorphology, Reinhold Book Corporation, New York. a Hamilton, D. H. and Meehan, R. L. , 1971 , Ground rupture in the Baldwin Hills : Science , Vol. 172 , Number 3981 . Harding, T. P. , 1973, :Newport- Inglewood trend, California; an example of wrenching style of deformation: American Association of Petroleum Geologists , vol. 57, pp 97-116 . Adft 65 Hazenbush, G. C. $ Allen, D. R. , 1958 , Huntington Beach oil field: D.O. G. vol . 28 , # 1 . Hill , Mason L. , 1971, Newport- Inglewood zone and mesozoic subduction , California: Geol . Soc. American, vol . 82 , pp 2957-2962 . Hunter, A. L. $ Allen, D. R. , 1956 , Recent developments in West Newport oil field : D. O. G. vol . 42 , # 2. • Jahns , R. H. , Hill, M. L. , et al , 1971 , Geologic structure of the continental shelf off San Onofre ; regional relationships and influence on seismicity : Stanford University Board of Technical Review. Kew, William S. , 1923, Geologic evidence bearing on the Ingelwood earthquake of June 21 , 1920 : Seis . Soc. of America Bull . vol . 13. Lawmaster, H. V. $ Company, Inc. , 1973, Seismicity study, Tract 7495, Huntington Beach, California: for Signal Landmark Company. • Ledingham, G. W. , 1973, California Division of Oil $ Gas , August 27, 1973, personal communication. Leighton-Yen $ Associates , 1973 , Seiches in Vail Lake, Rancho California: prepared for Kaiser-Aetna. 46 L. A. District, Corps of Engineers , 1971, Preliminary flood insurance study, Huntington Beach, California: for Federal Insurance Administration. Matthiesen, et al , 1972, Criteria for the evaluation of the safety I• of nuclear power stations during earthquakes : School of Engineering and Applied Science , University of California, Los Angeles , California. McCulloh, Thane H. , Simple bouguer gravity and generalized geologic map of the Northwest part of the Los Angeles basin: U. S. G.S. Geophysical Investigation GP149. Miller, R. E. , 1966, Land subsidence in southern California: in Engineering Geology of southern California Association of Engineering Geologists . Murray-Aaron, Eugene R. , 1947, Tideland pools of Huntington Beach oil field: D.O. G. vol . 33, # 1 . Neumann, F. , 1954, Earthquake intensity and related ground movement, University of Washington Press , Seattle, (1954) . a • 66 Newmark, N. M. I. and W. J. Hall, 1969, Seismic design criteria for nuclear facilities : 4th WCEE, Santiago , Chile . Page, et al , 1972, Ground motion values for use in the seismic design of the Trans-Alaska pipeline system: Geol. Surv. Circ. 672 . Poland, J. F. , 1947, Summary statement of groundwater conditions and saline contamination along the coast of Orange County, California : Orange County Water District. Poland, J. F. , 1959, Hydrology of the Long Beach-Santa Ana area, California: USGS water supply, 1971. , Piper, A. M. , 1956, Groundwater geology of the coastal zone • Long Beach-Santa Ana area, California: USGS water supply paper 1109 . Raichler, F. , 1972 , Discussion of tsunami-responses of San Pedro Bay and Shelf, California: Proceedings of the American Society of Civil Engineers , (WW1) . S Richter, C. F. , 1958, Elementary seismology: W. H. Freeman & Company, San Francisco. Ross , Grant A. 1968 , Case studies of soil stability problems result- ing from earthquakes : thesis Univ. of California at Berkeley, unpublished Ph.D thesis . Schnabel, P. B . and Seed, H. B. , 1972 , Acceleration in rock for earthquakes in the Western United States : Report No. EERC 72-2 , Earthquake Engineering Research Center, University of California, Berkeley. Schoellhamer, J. E. $ Woodford, A. 0. , 1951 , Los Angeles Basin: USGS OM 117 . Seed, H. G. , Idriss , A. M. , and Kiefer, F. W. , 1969 , Characteristics of rock motions during earthquakes : ASCE Journal of Soil Mechanics and Foundations , Div. , SMS. Seed, H. B . , Idriss , A. M. , 1971 , Simplified procedure for evaluation of soil liquefaction potential : Proceedings of ASCE , Journal of Soil Mechanics and Foundations Division. 1967, Analysis of soil liquefaction - Niigata earthquake: Proceedings of ASCE, Journal of Soil Mechanics and Foundations Division. Seed, If. B . and Lee, K. , 1966, Liquefaction of saturated sands during cyclic loading: Proceedings of ASCE, Journal of Soil + Mechanics and Foundations Division. A!Wk i 67 Shepard, F. P . , MacDonald, G. A. and Cox, D. C. , 1950, The tsunami of April 1 , 1946 : Bull . Scripps Institution of Oceanography of the University of California, La Jolla, Calif. , vol . 5, no . 6 , pp. 391-528. University of Calif. Press , Berkeley and Los Angeles . Soil Conservation Survey, 1919, Soil survey of the Anaheim area, California: U. S . Dept . of Agriculture . Taber, Stephen, 1920 , The Inglewood earthquake in southern California June 21, 1920 : Seis . Soc. of American Bull . vol. 10. Troxel et al , 1938 , Floods or March 1938, southern California: USGS water supply paper 844. • Townley, S. D. and Allen, M. W. , 1939, Descriptive catalog of earth- quakes of the Pacific Coast of the United States 1769-1928: Seis . Soc. Amer. Bull . vol . 29 , no. 1 . U. S. Army Corps of Engineers , 1959 , Beach erosion control report on ` cooperative study of Orange County, California. and Dames $ Moore, 1971 , National shoreline study - California regional inventory. Wentworth, C. M. et al , 1970, Preliminary geologic environmental map of the Greater Los Angeles area, California: A.E.C. TID-25363, 1 : 250 , 000 . Wiegel , R. L. , 1964 , Tsunamis , storm surges and harbor oscillations : Oceanographic Engineering, Prentice-Hall, Inc. Englewood Cliffs , New Jersey. , 1970 , Tsunamis : in Earthquake Engineering, Prentice-Hall, Inc. , Englewood Cliffs , New Jersey. Wilson, B. W. $ Torum, A. , 1968, The tsunami of the Alaskan earth- quake, 1964 ; engineering evaluation: U. S. Army Corps of +� Engineers , Coastal Research Center, Tech. Memorandum No. 25. Wood, H. 0. , and Heck, N. H. , 1966, Earthquake history of the United States , Part II , stronger earthquakes of California and western Nevada : U. S . Dept. of Commerce , E.S.S .A. Yerkes , R. F. , 1965 , Geology of the Los Angeles Basin - an intro- duction: USGS Prof. Paper 420-A. Af 216p, 68 • APPENDIX C • AERIAL PHOTOGRAPHS Year Flight Number Scale Agency j 1928 C-300 1" = 1500' Fairchild C-135 1" = 1500' Fairchild 1932 2389 1" = 1000 ' Fairchild 1938 5029 1" = 2500 ' Fairchild 1947 11730 1" = 600' Fairchild • • • 69 HUNTINGTON BEACH PLANNING DEPARTMENT 3P RICHARD HARLOW Director * EDWARD SELICH Senior Planner * MONiCA FLORIt`N Associate Planne. DAVE EADIL A&cociatePlanner AL MONTES Assistant Planter MAUREEN WILD Assistant Planner SAVOY BELLAVIA Assistant Planner FRED&Is T TER Assistant Planner .OqN COPE Assistant Planner EMILiE .f'€3HNSON Planning Aide DAN BRUENING PlsnningAidA 808 f IRBY Planning Aida SERGIO MARTINEZ Planning Aide 4 TF O;M JAGOSS 111W'ator * CEORGE ERMiN Plarnn;n;, Draftarnan * BOB SIGMON P4ar'ning Dmftstnan *ALAN LEE. Planning Draftsman JUKE ALLEN Administrative Secretary JANA HARTGE P(mcipsl Cie* SUSAN PIERCE �cretan'-Typist CI ELA CANIPAGNE t5ecretary * MAR'Y CARES€NAL Cl tk Typist PaIti6pewit-Staff DOUGLAS MORAN Chief Geologist, Leighton—Yen&Associates REPORT BY: ADVANCE PLANNING STAFF AND LEIGHTON—YEN & ASSOCIATES FEBRUARY 1974