Mike Stickney Montana Bureau of Mines and Geology Earthquake Studies Office
DIVISION OF MINES AND GEOLOGY · 8/6/1988 · slale of c.a.llfornia~thf resources agency...
Transcript of DIVISION OF MINES AND GEOLOGY · 8/6/1988 · slale of c.a.llfornia~thf resources agency...
SlAle OF C.A.LlFORNIA~THf RESOURCES AGENCY
D\:P.A.RTMENT OF CONSERVATION
DIVISION OF MINES AND GEOLOGY BAY .A.REA REGIONAl OFFICE
380 CIVIC Ofi:IVE, SUITE 100
PLEAS.A.NT HILL, CA 94523-1997
PHONE, (415) 646-5920
ATSS -'99-5920
Mike Johnson Engineering Geology Group Dept. of Public Works County of Los /illgeles P.O. Box 1460 Alhambra, CA 91802-1460
Dear Mr~ Johnson:
• Gf:ORGE OE.UKMEJ IAN, Gc;i~l'f'lor
November l, 1988
we are placing on open file the following reports reviewed and approved by the County of Los lillgeles in compliance with the Alquist-Priolo Special Studies zones Act:
Geologic and seismic investigation for porposed residential development, Tract 19278 1 I,ots 23 & 24, Lake Elizabeth area, Los Angeles county, CA1 by Keith w. Ehlert, 8/19/88.
Geologic and seismic investigation for proposed residential development, Tract 19839, Lot 141, Lake Elizabeth area, Los Angel@s county, CA1 by Keith w. El\lert1 3/28/88.
Geologic and seismic investigation for propcsed rE!Sidential development, Tract 28075 1 Lat 2 1 Lake Elizabeth area, Los Angeles county, CA; by Keith w. E~lert1 8/6/88.
EWH: lr
cc: A-P file (3) v'
Sincerly,
Earl w. Hart, CEG 935 senior Geologist & Program Manager
• ENGINEERING GEOL.OGY QFIOIJP GEOLOGiC REVIEW SHEET
1213) 1313-2828 COUNTY OF LOS ANGE'. LES 0EPAAIMENT OF PUBLIC WORKS
550 SO. VERMONT AVE_, LOS ANGELES, CA 90020 0 Tract/PM ~2~8~0~7~5~--------- Lot(s) 2 Parent Tract Site Address 14533 Flintstone Geologist Keith Ehlert
LocatiorLake Elizabeth Developer/owner Kitt White
Soils Engineer ------------Engineer Joe Beckham
PLAN CHECK NO. OR OATE OF REPORT(S)
Review of: OGrading P .C. No.
J@Buildin9 P.c. No. --""2..,4 ... 6 • .,1.__ __ ~5,,.,f-1_,,18U-//·,.s""s.__ _ _..s,..F ....... R -· DGeologic Site Inspection Only P.C. No.
D 8.0 ist. Office ----
f XXXX NF_~-SHEET -1- OF 1
DISTRIBUTION;
_£ Dist. Engineec 1.. Geologist - Soils Engineer _1_ Geol. Group File
- Grading Section _1_ State of Cali!.
:laXGeologic Report Dated ---J1A.:i.1l~l;lifl'~llilit~.10;6,.,,.-1.._g~SocB>--41-'>91-i3~3;i-8=8--------------------0Soils Report Dated
Action:
© Prepare
48-00)
OGeology & Soils Report Dated
OPlan is geologically approved mP!an approved geologically subject to conditions below OSec. 309 Code requirements met (not met)
D Plan is not approved for reasons below O Submit plans for recheck
All recommendations put forth in the referenced report must be complied with. The propoted structure must be designed to withstand a maximum
repeatable ground acceleration of .4Sg (page 13 of the referenced report)
d by ___________ Date _...,l_O_-_l _1_-_f_~_
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August 6, 1988
Mr. Kirt White 2214 West Avenue 0-4 Palmdale, CA 93550
KEITH W. EHLERT Consulting Engineering Geologist
14 5 5 3 J-JLd-s-f6t.9-r- Q,. it' d,~ld
s. f· \).
rnrn@rnawrnoo Project No. 1933-88 StP 15 1988
PROCESSING CENTER LAND DEV. DIV •
SUBJECT: GEOLOGIC AND SEISMIC INVESTIGATION FOR PROPOSED RESIDENTIAL • DEVELOPMENT
Tract 28075 Lot 2 Lake Elizabeth Area Los Angeles County, California
• Dear Mr. White:
Pursuant to your request, the accompanying report has been prepared for the purpose of providing geologic information pertaining to development of the subject site.
a If you have any questions regarding the information presented in this report, please call my office.
ectfully submitted
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• 25500 Hawthorne Blvd., Suite 1240 • Torrance, CA 90505 • (213) 378-4146
• P.N. 1933-88 Page 1
• INTRODUCTION
• PURPOSE
e The purpose of this investigation was to obtain sufficient geologic
information to estimate on-site geologic conditions with respect to
propsed development of lot 2 of tract 28075 with a single family
e dwelling.
• SCOPE OF WORK
The scope of work performed for this investigation included the
e following items:
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* Gathering and review of iiVailable published and unpublished
reports and maps pertllining to the geologic conditions on the
site and in surrounding ilreas.
• Geologic review of aerial photographs of the site area.
Aerial photographs used during this investigation were reviewed
at Los Angeles County Department of Building and Safety offices
located at 550 So. Vermont Ave., Los Angeles, California.
• Subsurface explorlltion consisting of one long exploratory
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P.N. 1933-88 Page 2
trench. The trench was excavated with a backhoe .
* Preparation of this report with maps, trench and test pit
logs, and other graphics to present the findings and
recommendations .
SITE DESCRIPTION
The site consists lot 2 of tract 28075 located along the northerly
side of Flintstone Drive, Lake Elizabeth area, Los Angeles county,
e California. Figure 1 shows' the estimated geographic location of the
site.
e Generally, the site slopes gently northerly and was undeveloped at the
time of this investigation. The site appeared to have been recently
plowed .
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P.N. 1933-88
-·- ------ --··---- -------·~-....,
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~LAM~NTES • . . i
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FIGURE 1
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• P.N. 1933-88 Page 4
• GEOLOGY
• GEOLOGIC SETTING
e The site is located in the westerly portion of Leona Valley. Leona
Valley is a fault-controlled topographic trough within the active San
Andreas fault system. At many locations within the area bedrock has
e been pervasively fractured, sheared and deformed and different rock
types have been brought in contact by faulting. The San Andreas fault
is an active fault .
• The site is located within an area designated as a Special Studies
Zone. Such Special Studies Zones have been designated along known
e active faults in California under the Alquist Priolo Special Studies
Act which was signed into law March 7, 1973. The purpose of this act
is to prohibit the location of structures for human occupancy across
e traces of active faults. Figure 2 shows the location of the site
relative to the boundaries of the Special Studies Zone.
e The Lake Hughes Quadrangle of the Alquist Priolo Special Studies Zones
maps shows what appears to be a trace of the San Andreas fault as
trending about through the site (Figure 2). The possible fault trace
e is shown as dashed, indicating the line was placed based on aeerial
photo linaments that were not field checked. Barrows et al (1985)
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MODIFIED FROM ALQUIST PRIOLO MAP • LAKE HUGHES QUADRANGLE
P.N. 1933-88
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FIGURE 2
• P.N. 1933-88 Page 6
• does not show a fault trace as trending through the site. Barrow shows
e a fault trace located about 300 feet southerly of the site.
• SITE GEOLOGY
Barrows et al (1985) indicates that the site is underlain by bedrock of
e the Anaverde Formation. Figure 3 is a copy of a portion of Barrows
map.
e lnformation obtained from the exploratory excavations indicates the
proposed building site area is underlain by what appeared to be
a somewhat chaotic admixture of different rock types, including arkose,
e siltstone-claystone, and fine grained sandstone. The arkose and
sandstone appeared pervasively jointed and could be broken out 1n
relatively small chunks. Contacts between the different units appeared
e somewhat sharp, but no gouge or clearly identified faults were observed
in the contact zones. In general, the material in the test trench
appeared "melange-like". The claystone appeared pervasively sheared
e and contained numerous discontinuous random polished surfaces.
Figure 4 is a sketch-log of the features observed in the exploratory
e trench .
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Modified after B~~rows et al, 1985 ·
1-----------.----------'"""I Figure 3 KEITH W. EHLERT
Consulting Engineering Geologist P.N. 1933-88
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TRACT N2. 28075 M. B. T23 - PGS. 110 TO llZ
LOTS 1 TJ> 33, 5',54 a,.o n"' 7T
Thi• i:li ~ • MM"We'Y 9'I tlMI .. nd, .,t ie eompi1ad IO' ifi.forn·u111ion anly • .., ;. ii • 11ar1 of thti rnon .. .,at.MC't' •o whM;:~ 11 1111aw tM attKt..d .
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FIGURE 5
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P.N. 1933-88 Page a
STRUCTURE
No features were observed in the exploratory trench which indicates a
major through-going fault trends through the site, nor were any
• features observed during review of aerial photographs which indicate a
major fault trace trends through the site. Although the clayey
material observed in the trench contained randomly oriented
• discontinuous polished surfaces (shear surfaces), no features were
observed which indicate a major through-going fault trends through the
site .
• The melange-like features observed in the test trench are likely the
result of severe deformation due to regional compression. The site is
e located on a generally easterly-westerly trending topographic ridge
which is likely a compression ridge resulting from regional tectonic
pressures generated along the San Andreas fault .
• The sheared claystone observed in the trench may represent highly
weathered sandstone or may represent original sedimentary claystone
9 materials.
It is important to recognize that the site is located within an active
e fault zone. During the next 111ajor earthquake on the San Andreas fault
in the site area it is likely the site will be subjected to severe and
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• potentially highly destructive ground shaking.
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SEISMICITY
INTRODUCTION
As previously indicated, the site is located within the San Andreas
fault zone and is located in an area that is very tectonically active.
e Two major potential hazards associated with active faults which could
have a direct influence on the site are surface ground rupture and very
severe ground shaking. It is likely that for sites located in close
e proximity to active faults or located within active fault zones, the
most severe damage to structures will result from ground motion
(shaking) and permanent ground deformation as opposed to ground
e ruptures. Such occurrences were demonstrated during the 1971 San
Fernando earthquake .
• GROUND MOTION
e The severity of ground motion from an earthquake can be charlilcterized
either qualitatively from the observed or expected effects of shaking
on man and hie structures, or quantitatively from parameters that can
e be instrumentally recorded or evaluated. Quantitative parameters are
commonly util.LZed 1n design of structures. Experience has shown that
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P.N. 1933-88 Page 11
horizontal acceleration may be one of the more critical factors with
regard to damage caused by ground shaking resulting from earthquakes .
As such, the protential for on-site acceleration resulting from an
earthquake on the San Andreas fault system is evaluated and estimated
below .
Greensfelder (1974) indicates that data on the relationship between
• rock acceleration, earthquake magnitude and fault distance are scanty,
especially for accelerations greater than .2g. This is because few
strong-motion records have been obtained within 20 miles of the
• causative faults tor earthquakes of magnitude 6 or greater. In a
report summariZing rock acceleration data for the western United
States, only ten values of acceleration greater than .2g are shown
• (Schnabel and Seed, 1973). These are for earthquakes of magnitude 5.6
to 6.6. From these and other data, Schnable and Seed (1973) have
developed empirical acceleration versus distance curves for events of
e Magnitude 5.6 to 6.6. Their curve for magnitude 7.6 is an
extrapolation based entirely on data obtained at distances between 35
and 100 miles from the causative fault. The curve for 8.5 earthquakes
• is simply estimated because no near-fault data are available for such
large earthquakes.
• .Joyner et al (1981) use newly available data to extend prediction
equations to zero distance from the causative fault. However, it
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• appears their acceleration curves for distances of less than about 30
• miles are based on earthquakes with magnitude less than 7.0. Within
about 1 mile distance their acceleration curves are almost flat,
indicating within about one mile of the causative fault acceleration
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does not significantly change with distance .
Campbell (1981) has indicated that in the near field acceleration is
independent of magnitude and distance from the causative fault. In
addition, many of the commonly used tables show peak acceleration as _
opposed to repeated ground accelerations. Plossel and Solssen (1974)
• have presented data that indicates for sites within about 20 miles of
the epicenter of earthquakes in California the repeatable high ground
acceleration averages about 65% of the maximum (peak) acceleration.
• They indicate this concept appears valid for earthquakes of magnitude
5.5+ to 7+, and for larger quakes a similar relationship probably
exists, but suffieient near-field data is not available. Plossel and
e Slossen (1974) conclude that a repeatable high ground acceleration may
more closely approximate a "design acceleration" than maximum or peak
accelerations. Page et al (1972) have noted that a single peak of
e intense ground motion (maximum or peak acceleration) may contribute
less to the cumulative damage potential than several cycles of less
intense shaking. Therefore, it appears that repeated high ground
• acceleration should be of greater concern in structure design than a
single peak of maximum acceleration .
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• It does not appear that adequate data is available to predict
I near-source accelerations. However, based on known available data, and
review of various rock acceleration versus distance and earthquake
magnitude tables, it appears that if a magnitude 8.0 earthquake were to
' occur on the San Andreas fault in the site area, a maximum or peak
acceleration of about .75g occurring at the site seems reasonable.
Using the concepts presented by Plossel and Slossen (1974), this
' corresponds to a maximum REPEATABLE acceleration of about .4Bg that
could be expected in the site area.
• it is important to recognize that the above evaluations are based on
very sparse data and much has to be learned about ground accelerations
resulting from earthquakes, especially in close proximity to the
causative fault, such ~s the site. for example, a peak acceleration of \
1.25g was recorded at Pacoima Dam during the San Fernando Earthquake
(the largest acceleration ever recorded). Although this apparent
anomalous reading may have been influenced by topographic and other
considerations, it does demonstrate that much more needs to be learned
regarding accelerations from earthquakes. In addition, during the
recent Whittier Narrows earthquake, a ground acceleration of about .6g
was measured in the Tarzana area of the San Fernal':'do Valley, when much
lower accelerations were measured much closer to the epicentral area.
An added consideration when evaluating peak versus repeated
accelerations is whether more than one "peak" acceleration might occur
• P.N. 1936~88 Page 14
• during one event. Such an occurrence appears to be a realistic
• possibility, especially for sites in close proximity to the San Andreas
fault .
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GROUND RUPTURE
The effects of ground rupture or ground cracking resulting from
earthquakes can have profound significance for buildings, including
single family dwellings such as proposed for the site. Earthquakes in
~ California can be accompanied by surface ruptures or severe ground
cracking. Surface faulting is rarely confined to a simple narrow line
nor is it necessarily restricted to known or identified fault traces.
• During the San Fernando earthquake, a relatively wide zone of fault
breakage occurred where no faults had previously been recognized. The
significance of this information with regard to the site is that it
• indicates that when an earthquake occurs, ground ruptures may not
necessarily be confined to known fault traces, but rather could occur
almost anywhere in the vicinity of the causative fault, including at
• locations where no known faults exist. As such, it is important to
recognize that although no active faults have been identified as
trending through the site during this investigation, the possibility of
• ground ruptures occurring within the site during an earthquake cannot
be ruled out .
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• As previously mentioned, it is also important to recognize that perhaps
• the greatest damage resulting from an earthquake could be the result of
severe ground shaking and ground deformation. Some modern wood-frame
houses, presumably built to code, collapsed as a result of shaking from
• the San Fernando earthquake, yet some structures located directly above
fault ruptures did not collapse. An added factor is duration of
shaking. Some earthquakes have a longer duration of shaking than
• others. It appears likely that during the next major event on the San
Andreas fault in the site area or 1n aouthern California, the duration
of ground shaking will have a direct influence on the severity of
• damage that occurs to atructures .
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• CONCLUSIONS AND RECOMMENDATIONS
• GENERAL
• The conclusions and recommendations contained in this report are based
on information provided to this consultant, information gathered,
geologic evaluations, experience and professional judgement. The
• recommendations contained in this report should be considered minimums
consistent with industry practice. Some degree of risk is associated .
with any development. More rigorous criteria could be adopted if lower
• risk of future problems is desired. Usually the lowest risk is
asociated with the greatest cost of development.
• No features were observed that indicate active faults trend through the
site. However, it is important to recognize that considerable risk is
associated with any a site located in, or close proximity to, an active
e fault zone. Although the risk of ground ruptures directly affecting
the proposed development can be reduced by avoiding building across
known active or potentially active faults, the possibility of ground
e ruptures occurring anywhere in proximity to an active fault, including
within the site, cannot be ruled out.
• It is a.lso important to recogni.ze that it is likely the greatest damage
resulting from an earthquake in the site area will be from severe
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ground shaking and possible permanent ground deformation. The San
Andreas fault is an active fault and it is likely a major earthquake
will occur on the San Andreas fault in the site area during the life of
the structure .
COMPLIANCE WITH CODE SECTION 309
Provided agency requirements are adhered to and good construction
practices are followed, as well as the recommendations in this report
• are followed, it is this consultants opinion that the site can be
developed without hazard from landslide, slippage or undue settlement
and can proceed without adverse impact on adjoining properties .
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• GRADING AND FOUNDATIONS
The project soils engineer should make appropriate recommendations with
regard to the suitability of on-site materials for foundation and/or
• fill support. All fill materials (other than minor landscape fills)
should be placed under the supervision of a soils engineer.
The project soils engineer should provide foundation design criteria
e for all structures, including retaining walls, etc .
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• A very important consideration is that the site is underlain by
I differing rock-types. It appears that t:he foundations for the proposed
structure will "straddle" the transistion between differing rock types.
It is important that the soils engineer take the differing
I characteristics of the these materials into account. Otherwise, there
could be a significant potential that the foundations will perform
differently from one portion of any structure to the next, possibly
resulting in cracking, etc.
The clays observed in the trench appeared highly expansive.
The project soils engineer should provide recommendations pertaining to
the steepness of any cut or fill slopes.
A mimimum of 20 feet horizontal distance between the bottom outer edge
of any foundations and any slope face should be maintained unless
otherwise recommended by a soils engineer.
A soils engineer should make recommendations with regard to bearing
values of natural and/or fill materials for foundation 6Upport.
It: is recommended that extensive water proofing be provided to
prevent moisture or water damage to the interior portions of the
structures it retaining walls will be used to form portions of the
• P.N. 1933-88 Page 19
• interior walls of the structure. The architect and/or engineer should
e provide details of the moisture proofing system to minimize risk of
dampness and/or direct moisture damage occurring. Even though it
appears groundwater may not be a significant problem at this site,
e extreme care should be exercised in sealing walls and floors against
water and water vapor migration .
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• DRAINAGE AND EROSION
The project civil engineer and project soils engineer should make
appropriate recommendations with regard to erosion of any natural or
e man-made elopes incorporated into the site development. The project
civil engineer should also make appropriate recommendations with regard
to site drainge and drainage control .
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FAULT HAZARDS SUMMARY
As previously discussed, no major through-going known active faults
were observed as trending through the site .
it does not appear that sufficient information is available to
• P.N. 1933-88 Page 20
• accurately predict near-source accelerations tor sites in close
e proximity to the causative fault. Existing information, including rock
acceleration versus distance and earthquake magnitude tables, suggests
that if a magnitude 8.0 earthquake were to occur on the San Andreas
e fault in the site area, a peak acceleration of about .75g could occur
on the site. It is important to l'ecognize that this evaluation is
based on l'eview of various tables which, for sites close to the
• causative faults and especially for large magnitude events, are
essentially extrapolated since near-soul'ce data is spal'se.
• The possibility of higher accelerations occurring cannot be ruled out.
The site will likely be subjected to severe ground motion during the
next major earthquake on the San Andreas fault in the site al'ea.
• although the possibility of ground ruptures occurl'ing within the site,
cannot be l'Uled out, it is likely that for sites located in close
proximity to active faults, the most severe damage to structures will
e l'esult from severe ground motion (shaking) and permanent ground
defol'mation as opposed to ground l'Upture.
e It is also important to l'ecognize that pel'manent changes in groundwater
level can occur as a result of earthquakes .
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P.N. 1933-88 Page 21
ADDITIONAL CONSULTING
Any additional consulting, such as for foundation reviews, grading plan
review, response to regulatory agency reviews, etc. will be performed
• on a time and expense basis .
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COMMENTS
The conclusions and recommendations presented in this report are based on research, site observations and limited subsurface information. The conclusions and recommendations presented are based on the supposition that subsurface conditions do not vary significantly from those indicated. Although no significant variations in subsurface conditions are anticipated, the possibility of significant variations cannot be ruled out. lf such conditions are encountered, this consultant should be contacted immeditately to consider the need for modification of the project .
This report is subject to review by regulatory public agencies and these agencies may require their approval before the project can proceed. No guarantee that the regulatory public agency or agencies will approve the project is intended, expressed or implied .
One of the purposes of this report is to provide the client with advice regarding geologic conditions on the site. It is important to recognize that other conultants could arrive at different conclusions and recommendations. No warranties of future site performance are intended, expressed or implied .
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REFERENCES REVIEWED
Barrows, A.G., Kahle, J.E., and Beeby, D.J., 1985, Earthquake hazards and tectoni~ his~ory of. the San Andreas fault: zone, Los Angeles County, CalJ.fornJ.a: Cal.if. Dept. Conservation Division Mines and Geology Open File Report 85-10 LA.
Beeby, David J., 1979, Geology and fault activity on the Lake Hughes segment of the San Andreas fault zone, Los Angeles County, California: Calif. Div. Mines Geol., Open File Report 79-2Lll.
Campbell, Kenneth W., 1981, Near-source attenuation of peak horizontal acceleration: Geol. Soc. America Bull., v. 71, no. 6, p. 2039-2070.
Greensfelder, Roger w., 1974, Maximum credible rock acceleration from earthquakes in California: Calif. Div. Mines Geol., Map Sheet 23 .
Joyner, William B., Moore, David M., and Porcella, Ronald L. 1
1981, Peak horizontal acceleration and velocity from strong motion records including records from the 1979 imperial valley, California, earthquake: U.S. Geo!. Survey Open Filo Report 81-365 .
Kahle, James E., smith, Drew P., and Beeby, David J., 1975, Geology of of the Leona Valley segment of the San Andreas· fault zone, Los Angeles County, California: Calif. Div. Mines Geol., Open File Report 77-2LA
Page, R.A., Boore, D.M., Joyner, W.B., and Coulter, H.W., 1972, Ground motion values for use in the seismic design of the Trans-Alaska pipeline system: U.S. Geol. Survey Circular 672, Washington D.C., 23p.
Plossel, Michael R., and Slosson, James E., 1974, Repaetable high ground acceleratins from earthquakes-important design criteria-: Calif. Geology, September.
Ross, Donald C., 1969, Map showing r~cently active fault breaks~ along the San Andreas fault between Tejon Pass and Cajon Pass: U.S. Geol. Survey Miscellaneous Invest. Series, Map 1553 .
Schnabel, P.B., and Seed, H.B., 1973, Accelerations in rock for 'earthquakes in the western United States: Bulletin of the Seismological Society of America, v. 62, p. 501-516.
Sieh, Kerry E. 1978, Pre-historic large earthquakes produced by slip on the San Andreas fault at Pallet Creek, California: Journal of Geophysical Research, v. 83, p. 3907-3939.
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Sieh, Kerry E., 1984, Lateral offset and revised dates of large pre-historic earthquakes at Pallett Creek, southern California: Journal of Geophysical Research, v. 89, p. 76~1-7670.
Weldon, Ray J. II, and Sieh, Kerry E., 1985, Holocene rate of slip and tentative recurrence interval for large earthquakes on the San Andreas fault, Cajon Pass, southern California: Geol: Soc. Am. Bull., v. 96, P 793-812.
Wenousky, Steven G., 1986, Earthquakes, Quaternary faults, and seismic hazard in California: Jour. Geophys. Research, v. 91, p. 12,587-12,631.
Youd, T.L., 1973, Liquefaction, flow, and associated ground failure: U.S. Geol. Survey Circular 688, 12 p.
Youd, T.L., and Perkins, D.M., 1978, Mapping liquefaction-induced ground failure potential: Proceedings of the American Society of Civil Engineers, Journal of Geotechnical Engineering Division, v. 104, no. GT4, p. 433-446.
Ziony, J.I., 1985, Evaluating earthquake hazards in the Los Angeles Region-an earth-science perspective: U.S. Geel . Survey Prof. Paper 1360 .