state of california-the resour.ces agency edmund g. … · 1979-01-31 · , state of california-the...
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STATE OF CALIFORNIA-THE RESOUR.CES AGENCY EDMUND G. BROWN JR., Governor
DEPARTMENT OF CONSERVATION
DIVISION OF MINES AND GEOLOGY SAN FRANCISCO DISTRICT OFFICE FERRY BUILDING SAN FRANCISCO, CA 9.t IT 1 (Phone 415-557..()633)
(Phone 415-557-0413)
Septerrber 1 O, 1980
Anthony B. Brown County of Riverside Riverside County Planning Dept, 4080 Lemon Street, 9th Floor Riverside, CA 92501
Dear Tony:
We are placing on open file the following report, reviewed and approved by the County of Riverside in compliance with the Alquist-Priolo Special Studies Zones Act:
Engineering geology investigation of a 10+ acre parcel, NE corner of Girard St. and Devonshire Ave., Hemet,-CA; by Rasmussen & Assoc.; Jan. 31, 1979 (County GR-171).
Also acknowledged is the Pioneer Consultants report for Parcel Map No. 14933 (Rancho California industrial Park), v.liich apparently lies outside of our Special Studies Zones. It will be filed informally.
EWH/fn 1
cc: A-P file (2) /
Sincerely yours,
EARL W. HART Office of the State Geologist CEG 935
, STATE OF CALIFORNIA-THE RESOURCES AGENCY EDMUND G. BROWN JR., Governor
DEPARTMENT OF CONSERVATION
DIVISION OF MINES AND GEOLOGY SAN FRANCISCO DISTRICT OFFICE FERRY BUILDING
SAN FRANCISCO, CA 94111
(Phone 415-557-0633}
(Phone 415-557-0413)
August 21, 1980
Anthony B. Brown County of Riverside Riverside County Planning Dept. 4080 Lemon Street, 9th Floor Riverside, CA 92501
Dear Tony:
We are placing on open file the following report, reviewed and approved by the County of Riverside in compliance with the Alquist-Priolo Special Studies Zones Act:
Engineering geology investigation, Tentative Tract 15313, SE of intersection of Mayberry Avenue and Pleasant Street, Hemet, CA; by Rasmussen &Assoc.; April 21, 1980 (County GR-210).
In checking my "hold" file, I note that we received no report with your letter of Jan. 8, 1980 re Tract No. 14142, County GR-171 (Neste, Brudin; Stone, Hemet).
EWH/fn l
cc: A-P Fi le (2) y
Sincere 1 y yours,
EARL W. HART Office of the State Geologist CEG 935
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Gl?-17/ GARY S. RASMUSSEN & ASSO.CIA TES /ENGINEERING GEOLOGY
1906 SO. COMMERCENTER EAST. SUITE 207 • SAN BERNARDINO, CA 92-408 • (71.4) 888-2422. • t71.4) 82!5-90!52
January 31, 1979
Neste, Brudin & Stone, Incorporated P.O. Box 851 Hemet, California 92343
Attention: John Brudin
Project No. 1443
Subject: Engineering Geology Investigation of a 10±-Acre Parcel, NE Corner of Girard Street and Devonshire Avenue, Hemet, California.
We have conducted a geology investigation of the site in accordance with
your request. The primary purpose of our investigation was to determine
if any active faults pass through the property and to relate engineering
geologic conditions of the site to future development. The northeast
portion of the site lies within a Special Studies Zone as outlined by the
State of California. A .200-scale plat map, provided by your firm, was
used in our investigation. Proposed development and grading plans were.
not available, but creation of level pads for building foundations should
result in maximum cut and fill slopes less than 10 feet in height. The
approximate location of the site is shown on the index map on page 2.
The northeast portion of the site lies within a zone of suspected active
faults as defined by the Alquist-Priolo Special Studies Zones Act
(Enclosure 3). Suspected, northwest trending faults are shown passing
in the immediate vicinity of the 2000-scale Special Studies Zone map
(CDHG). The approximate limits of the Special Studies Zone are shown on
the index map on page 2 and on Enclosure 1. The index map is a reproduc
tion of the Riverside County Seismic Safety Element (after the CDMG Alquist
Priolo Special Studies Zones map) and does not contain modification of
fault locations as determined by previous investigations. The northwest
trending Casa Lorna fault is sho~~ to pass within 200 feet northeast of
the parcel. The Casa Loma fault is an en echelon feature in this area,
and its exact location is not apparent at the ground surface. Previous
subsurface geology investigations have been conducted north, northeast,
... -····;.····
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• • • • • ': ·· . .... ::~? ~
B
INDEX MAP Howard Rose Co. 10±-Acre Parcel
Hemet, California Legend
CACI/It
Alquist-Priolo Special Studies Zone
_ . _·-?Fault, dashed where · approx., dotted where buried, queried where in doubt Alluvium of intermediate thickness (200-2000 1
)
Thick alluvium and soft sediments (2000'+) Slope instability
1 very low 2 low
Base I.lap: Riverside County Seismic Hazards /.lap . (Envicom) Sept. 1976
Scale 1"~2000' Project No. 1443
-2-
.. .·: ........
8 0 ~
' 0
~=~'7li~~~s~,~~~~"'==j'Vi'~~~~~~~~~~=="'~v~'~" " . .
Gary S. Rasmussen & Associates, Inc.
Neste, Brudin & Stone, Inc.-10±-Acre Parcel-Hemet January 31, 1979
Project No. 1443
and southeast of the site. One continuous backhoe trench was excavated
across the Special Studies Zone portion of the site as shown on the enclosed ..
200-scale map. 11iis trench was excavated in a general northeast to south
west direction in order to intercept any northwest trending active faults
that may lie within the Alquist-Priolo Special Studies Zone portion of the
site.
SITE INVESTIGATION
A geologic field reconnaissance of the site and surrounding area was
conducte4 during January 1979. In addition to our field work, our investi
gation included review of stereoscopic pairs of aerial photographs flown
in 1972; review of pertinent geologic literature and maps, including inves
tigations previously conducted by this firm of sites in the nearby
vicinity; excavation of one continuous trench on the site; and review of
seismic information including r~corded, historic earthquakes. A list of
references is enclosed (Enclosure 4).
The site currently contains the main office of the Howard Rose Company, Inc,,
which includes office buildings, warehouses, experimental nursery stock,
and three residences. Several· buildings had been dismantled and removed
prior to our investigation.
The methodology used for the subsurface portion of our geologic investi
gation was to excavate a trench to a depth of 10-12 feet across that
portion of the parcel that lies within the Alquist-Priolo Special Studies
Zone (plus an additional30 feet) in a manner that would intercept any
northwest trending faults (direction of known faulting in the area). This
procedure enables a visual inspection of the subsurface materials for
faults and fault related features. Trenching of sediments, such as exist
on the site, is consistent with the current state-of-the-art for inves
tigating recency of faulting for the type of use intended for the site
-3-GA.RY S. RASMUSSEN & ASSOCIATES
Neste, Brudin & Stone, Inc.-10±-Acre Parcel-Hemet January 31, 1979
Project No. 1443
(residential). One continuous backhoe trench, with a total lineal
footage of 501 feet, was excavated on the site. This trench was entered
and examined in detail for any evidence of Holocene faulting (Enclosure 5),
with none found. .The exact age of sediments at a depth of 10-12 feet
throughout the site is not known but is estimated to be approximatey 300-400
years in age. Sediments estimated to be less than 100 years in age have
been ruptured by both the Casa Loma and Claremont traces of the San
Jacinto fault zone in the Hemet area.
SITE GEOLOGY
The site is located on an alluvial plain in the San Jacinto Valley,
located within the City of Hemet, and directly west of Park Hill. The
regional ground surface slopes downward towards the northwest at a rate
of approximately 1 percent. The site contains a northwest flowing drainage
which enters through the central portion of the east property line and
trends through the property towards the northwest (Enclosure 1). The
alluvial sediments on-site were probably deposited during flooding from
Bautista Creek, Bautista Wash, and the San Jacinto River in the historic
past. Bautista Wash passes along ·the northeast side of Park Hill,
approximately l mile northeast of the site; and the San Jacinto River is
approximately 2 miles northeast of the site. The site is entirely under
lain by Holocene alluvium. The closest older geologic units occur in
Park Hill, approximately 1600 feet to the northeast, where sedimentary
rocks of Pleistocene age occur (Bautista Beds, Frick, 1921) and in the
bedrock hills, approximately 2 miles south. Igneous granitic rocks occur
in the hills to the southwest (of probable Cretaceous age).
The block of land between the Casa Loma fault, northeast of the site, and
the Claremont branch of the San Jacinto fault, approximately 3 miles
northeast, is a large graben (downthrown block of land between faults)
that has historically undergone subsidence of up to 4 feet in some places.
Both the Casa Loma and Claremont faults are part of the San Jacinto fault
-4-GARY S. RASMUSSEN & ASSOCIATES
Neste, Brudin & Stone, Inc.-10±-Acre Parcel-Hemet January 31, 1979
Project No. 1443
zone (Sharp, 1975). The graben between these faults is underlain by
several thousand feet of alluvial sediments; whereas, the alluvial
sediments southwest of the Casa Loma fault (site area) only continue to
depths of approximately 500 feet (Fett, 1968). Igneous bedrock hills are
located just southwest of the Casa Loma fault. Metamorphic and igneous
rock, regionally capped by Pleistocene sediments, are located along the
northeast side of the Claremont fault.
The site lies approximately 1,600 feet southwest of the base of Park Hill.
Park Hill is an elongate hill raised by seismic activity along the Casa
Loma fault. Elongate hills, such as Park Hill, and closed depressions
are common in areas where strike-slip faults en echelon or change direc
tion. The exact location of all the faults in the immediate vicinity has
not been determined from trenching and is not obvious at the surface.
Because of the distinct sedimentary layers observed in the trench and the
continuity of these layers, together with previous investigations of sites
located immediately to the east, southeast; and north of the site (Rasmussen,
October 29, 1975; May 10, 1977; January 17, 1979), it appears the trace of
the Casa Loma fault in this area is an en echelon feature that probably
passes approximately 1,900 feet northeast of the northeast corner of the
site.
The immediate area is characterized by an irregular drainage pattern, with
numerous east-west and northwest flowing drainages. Previous trenching by
this firm across some of these drainages between the site and Florida
Avenue to the southeast, together with trenching of this parcel, indicates
most of the drainages are not directly controlled by faulting (all
drainages in the vicinity are not fault scarps). Similar, older drainages
existed in the same area but at different locations, as documented in our
report dated October 29, 1975 of a site located due east of this investi
gation, on the west side of Yale Street, north of Devonshire.
-5-G-AR.Y S. R.AS11.4USSEN & ASScx::::IATES
Neste, Brudin & Stone, Inc.-10±-Acre Parcel-Hemet January 31, 1979
TRENCH LOGS
Project No. 1443
The materials encountered in the trenches were generally fine-medium
sands and clay with a localized area of coarse-grained sands underlying
a current channel. Any faulting through the site should have disrupted
these distinct beds.
The drainage passing through the site appears"to.be·a very recent and_ possibly
historic origin, with the mat~rials within the drainage consisting of
fine-medium sands underlain by massive, coarse sands to a depth of approxi
mately 7 feet below the existing ground surface. Due to current seasonal
rains, the stream channel was flowing at the time of our investigation.
The trench was deepened to a depth of approximatley 12 feet at that location.
There was continuity of beds on either side of the drainage, indicating
no.vertical offset of these beds has occurred.
SEISMIC SETTING
A northwest trending branch of the San Jacinto fault zone, the Casa Loma
fault, is believed to pass northeast of the northeast corner of the site,
based on the en echelon fault scarp located just west of San Jacinto
Street and a subsurface investigation northwest of Menlo and Park Avenues.
Numerous trenches across the Casa Loma fault in the Hemet area by this
firm reveal fault rupture within llz feet of the surface in Holocene
alluvium. Therefore, the fault is considered to be active, having under
gone very recent and historic surface rupture.
Other active branches of the San Jacinto fault zone are known to be
located approximately 3 miles to the northeast. There may be other
active traces of this fault zone between these two main faults (Casa
Loma and Claremont), such as the possible fault along the northeast side
of Park Hill. However, trenching for Special Studies Zone reports on
file with Riverside County have not yet encountered it.
-6-GARY S. RASll.dUSSEN & ASScx::;IATES
Neste, Brudin & Stone, Inc.-10±-Acre Parcel-Hemet January 31, 1979
Project No. 1443
Numerous other active faults are located within the general region1
such as the Elsinore and San Andreas fault zone, but because of their
distance from the site, they are not considered significant compared to
the nearby branches of the San Jacinto fault zone.
A summary of major faults and their distances from the site is shown in
the following table:
FAULT
Casa Loma
Claremont
San Andreas (Banning)
Chino-Elsinore
Cucamonga
SEISMIC HISTORY
DISTANCE FROM SITE (MILES)
_adjacent-1,900 feet NE
3 NE
161'> NE
20 SW
41 NW
At least two destructive earthquakes have occurred historically (1899 and
1918) along the San Jacinto fault zone in this area. Both of these
earthquakes resulted in damage to buildings in the San Jacinto-Hemet area
and caused complete failure of many. The most recent, large earthquake
along the San Jacinto fault zone was a Richter 6.5 event, located in the
Anza-Borrego Desert in 1968. Earthquakes of a s_imilar or larger size
have occurred along this fault,zone on the average of once every S to 6
years since 1899 (Lamar, et.~., 1973).
Observation of folded bedding and local liquefaction effects on sand
layers in several trenches in the valley suggest that an earthquake
similar in size to the 1899 and 1918 events may have occurred in the area
approximately 200 to 300 years ago. Fault rupture of material below a
depth of 5 feet, but not above, where other faulting in the same trench
extends to near the surface may indicate yet another large earthquake
in the valley, between the historic ones and the disturbed bedding evidence.
-7-GA.R.Y S. RASMUSSEN & ASSOCIATES
Neste, Brudin & Stone, Inc.-10:!:-Acre Parcel -Hemet January 31, 1979
SEISMIC ANALYSIS
Project No. 1443
Significant earthquakes affecting the site are likely to occur on the San
Andreas and San Jacinto fault zones during the life of any structures to
be built on the site. Recurrence intervals for maximum probable earth
quakes cannot yet be precisely determined from a statistical standpoint, as
recorded information on seismic activity does not encompass a sufficient
span of time. However, based on information available at this time, it
is our opinion that a Richter magnitude 7.0 earthquake originating along
one or more branches of the San Jacinto fault zone (includes Casa Loma
and related faults on-si t.e) should be expected within the next 100 years
(at least 50 percent chance of occurrence). An earthquake of this magnitude
can be expected to produce maximum peak accelerations in bedrock under the
site of approximately 0.7g (Schnabel & Seed, 1973). This acceleration
should not necessarily be used as a design value, as it is a peak accelera- .
tion and is estimated for bedrock, which is estimated to be at least a: few
hundred feet beneath the surface. A corresponding maximum repeatable
acceleration for bedrock under the site would be 0.46g. These accelerations
should be considered an aid in the evaluation of building design for the
site and are not intended to be used as a design value in the Uniform
Building Code formula.
FLOODING
The extreme northeast portion of the site lies within the. 100.-year flood
plain as outlined in the Riverside County Safety Element to the General
Plan (Enclosure 2).
Minor flooding could occur along and adjacent to the small tributary
traversing ·through.the east-central and northwest portions of the site.
-8-GARY S. RAS:hll:USSEN & ASSOCIATES
Neste, Brudin & Stone, Inc.-10±-Acre Parcel-Hemet January 31, 1979
GROUND WATER
Project No. 1433
The alluvial materials under the site probably continue to depths of
300-500 feet. The Casa Loma fault forms a barrier to the lateral movement
of ground water in the San Jacinto Valley (Fett, 1968). No evidence of a
shallow ground water condition under the site was observed in the field
or on aerial photographs or in the immediate vicinity. The depth to
ground water is estimated to be more than 50 feet below the ground
surface. Liquefaction and other shallow ground water related hazards
are not expected to be a problem on the site.
CONCLUSIONS
The site is estimated to· lie within 1,900 feet of the active Casa Loma
fault a!'d approximately 3 mil_es squthwest of the Claremont branch of the
San Jacinto fault zone. Ground rupture due to surface faulting is not
expected through the site as no evidence of faulting through the site
was found in our investigation.
Severe seismic shaking of the site should be expected within the next
100 years from an earthquake on one of the nearby branches of the San
Jacinto fault zone (includes the Casa Loma fault).
Flooding of the site has occurred within the very recent geologic past,
as evidenced by the existing drainage and channel deposits observed in
the trenches. The northeast portion of the site lies within the 100-year
flood plain as outlined in the Riverside County Safety Element to the
General Plan (1976).
All but the extreme southwest portion of the site lies within the inundation
zone from failure of Little Lake Dam. The time of arrival of "first"
waters from failure of Little Lake Dam is estimated to be 140 minutes,
based upon the Riverside County Safety Element map to the General Plan
(Sept. 1976).
-9-0-AR.Y S. RASMUSSEN & ASSOCIATES
r
_j
Neste, Brudin & Stone, Inc.-10±-Acre Parcel-Hemet January 31, 1979
Project No. 1443
Liquefaction and other shallow ground water related hazards are not expected
on the site as the ground water table is estimated to be more than 50 feet
below the surface.
RECOMMENDATIONS
A maximum probable earthquake of Richter magnitude 7.0 is expected along
the San Jacinto fault zone in this area; therefore, we recommend human
occupancy structures be design~d accordingly.
The amount of peak flow along the tributary crossing the property in a
northwest direction should be determined and proposed structures protected
from flood hazards, if any.
DDB:GSR/mt
Enclosure 1: Enclosure 2: Enclosure 3: Enclosure 4: Enclosure 5:
200-scale map Flood hazards map Alquist-Priolo data References Trench logs
Respectfully submitted,
GARY S. RASMUSSEN & ASSOCIATES, INC.
;Q..C.~ Daniel D. Bush Staff Geologist
/;~/~ Gary S. Rasmussen ·· Engineering Geologist, EG 925
Distribution: Nes~e, Brudin & Stone, Inc. (8)
-10-0-.A.RY S. RASMUSSEN & ASSOCIATES
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HJCLOSURE 1
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GARY S. RASl!USSEN & ASSOCIATES, INC. l!o, .. ard Rose Co. lOLAcre Parcel
HeJ:Jet, California
Legend
Alquist-Priolo Special Studies Zone
1:::.-C"::::--_-_-_-_J Subsurface investigation trench "V'd"
Base J:ap: Riverside County Flood Control, Scale 1''=200 1
Project No. 1443
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ENCLOSURE 2 GARY S. RASHUSSEN & ASSOCIAT!'S, INC.
Howard Rose Co. 10:!:-Acre Parcel
Hemet, California
Legend
Approx. boundary of 100-year flood plain
Inundation zone from failure of Little Lake Dam
1773
. ·.
T 140 min Elapsed time from a dam failure of "first water"
---·-- -~ase _!lap: P-i ver~ ~-e C_?unty __ ---•
Safety Ele~ent to the General Plan, Sept. 1976
Scale 1"=2000' Project No. 1443
4 CAL ORNIA DIVISION OF MINES ANf 'EOLOGY SP 42
CALIFORNIA DIVISION OF MINES AND GEOLOGY PROGRAM FOR ZONING POTENTIALLY ACTIVE FAUL TS
Requirements of the Act
The Alquist-Priolo Special Studies Zones Act of I 972 {codified as Chapter 7.5, Division 2, of the California Public Resources Code) requires the Stale Geologist lo
1 .... Oelinea1e. by December _31, 1973, appropriately wide special studies zones to encompass all polentially and recently active traces of the San Andreas. Calaveras. Hayward. and San Jacinto Faults, and such olher faults ... lhal ... conslitute a paten· tial hazard to structures from surface faulting or fault creep".
2. Compile maps of special studies zones and submit such maps to affected cities, counties, and state agencies by 31 December 1973, for their review and comment. Following appropriale reviews, lhe State Geologist must provide "'official maps .. lo the allecled ci1ies, counties, and state agencies.
The State Geologist also is required lo "col)linually review new geologic and seismic data0 ii) order to revise the special studies zones or delineate additional zones_
The Act also requires Cities and Counties to exercise specified approval authority with respect lo real estate development or structures for human occupancy within the special studies zones. Further it requires specific Policies and Crileria to assist local jurisdictions in administering the Act from the Stale Mining and Geology Board.
Program for Zoning Potentially Active Faults
As required under the Act, the State Geologist (Chief of the California Division of Mines and Geology) established a program starting early in 1973 to delineate special sludies zones to encompass traces of potentially and recently active faults in California and to compile and distribute maps of these zones. A project learn, headed by this '"riter, \vas established within the Division lo d_evelop a program for delineation of the zones.
Initially, 175 maps of special studies zones were compiled for the San Andreas, Calaveras, l:layward, and San Jacinto faults. These zone. maps, issued as Preliminary Review Maps, '"'ere distributed for review by local and State governn1ent agencies on December 31, 1973. Following needed revisions as prescribed by law, Official Maps were issued on July I, 1974. Al that tin1c, the special studies zones became effective and implementation was 1equired by the affected Cities and Counticsz
A second set of zunc maps 'vas issued subsequently to de lineatc ne\v and revised zones--Pre li m inary Review Maps on July I, 1975, and Official Maps on January I, 1976. Zones delineated as part of this second issue.are shown on about 81 maps of new zones and 5 maps of revised zones. It is expected that additional Official
Maps of new and revised zones \yi!I be issued each year• on January I following issuance of a Preliminary Review Map on July I of the preceding year.
As of January I, 1976, approximately 256 Official Maps of_special studies zones have been issued and presently are in effect. These maps are identified by name on the Index to Maps of Special Studies Zones. The maps delineate zones for those faults identified in figure I. Approximately 23 Counties and 58 Cities are affected by the existing special studies zones. These Counties and Cities arc listed elsewhere in this report.
Faults zoned lo date by the Stale Geologist are iden· tified on figure I. Additional faults to be zoned in the near future include the Sierra Madre, Cucamonga, Raymond Hill, and Elsinore faults in southern California. There are many other faults in California that are potentially active (Jennings, 1973), and some of these may be zoned if determined to be "sufficiently active and well-defined as to constitute a hazard" (Chapter 2622 of the Act). As in the past, future zoning will be done on a priority basis depending on the availability of both data and funds.
I
Delineating the Special Studies Zones
Special st_udies zones are delineated on topographic base maps at a scale of I :24,000 (l inch equals 2000 feel). The zone boundaries are straight-line segments defined by turning points. Most of the turning points are intended 10 coincide with locatable features on the ground (e.g., bench marks, roads, streams), but neither these points nor the zone boundary lines between them have been surveyed in the field to verify their mapped locations. ·
The intent of the Alquist-Priolo Act is lo' provide for public safety from the hazard of fault rupture by avoiding, 10 the cxlent possible, the constructi.on of structures for human occupancy 3Stride hazardous faults. The faults sho,vn on the special studies zone maps are not precisely located on the maps, nor were they sur· veyed in the field during this study. Their locations were taken from the best geologic maps and reports available, and ploued according to the best judgment and skill of the California Division of Mines and Geology's staff geologist-compilers. The precise location and identification of hazardous faults within or near a zone of potentially active faults can be determined only through detailed geologic site investigations. Thus, this Act establishes the concept of a special s1udies zone-an area of limited extent centered on recognized faults--within which the danger of potential fault rupture is presumed. to exist until sho\\·n other\l.'ise by direct investigation. Potentially active faults other than those depicted on the maps, including branches and spurs of the named faults, may be present within the special s1udies zones. The zone boundaries delimit
6 CALIFL .. NIA DIVISION OF MINES AND G LOGY SP 42
the area believed by the State Geologist to warrant. special geologic investigations to confirm the presence or absence of hazardous faults. ·
Locations of special studies zone.boundaries are controlled by the position of the known traces of potentially active faults (defined below). However, the faults shown on the special studies zones maps were not field checked during the compilation of these maps. Because available fault data range widely in quality, and the locations of some faults are known imprecisely, the zone boundaries are positioned at a reasonable distance (about 660 feet, or 1/8 mile) on both sides of the trace of the nearest potentially active fault. However, zone boundaries generally are more or less than 660 feet away from mapped faults because of I) curved or multiple fault traces. 2) the practical advantage in keeping the number of turning points _to a reasonable minimum, and 3) the quality of the data dictates a narrower or wider zone.
Definitions
Fault and Fault Zone
A fault is defined as a fracture or zone of closely associated fractures along which rocks on one side have been displaced with respect to those on the other side. Most faults are the result of repeated displacement which may have taken place suddenly and/or by slow creep. A fault zane is a zone of related faults which commonly are braided and subparallel, but may be branching and divergent. A fault zone has s_!Rnificant width (with respect to the scale at which the fault is being considered, portrayed, or investigated). ranging from a few feet to several miles.
Fault Trace I
A fault trace is the line formed by the intersection of a faqlt and the earth's.surface. It is the representation ofa fau't as de(licted on a map, including maps of the special studies zones.
Potentially Active Fault
For the purposes of delineating special studies zones, any fault considered to have been active during Quaternary time (last 2 to 3 million years, figure 2}-on the basis of evidence of surface displacement-is considered by the State Geologist to be potentially active. An exception is a Quaternary fault which is determined, from direct evidence 1 to have become inactive before Holocene time (approximately the last 11,000 years). Such faults are presumed to be essentially inactive and most have been omitted from the maps. Although potentially active faults shown on the maps may have been active during any part of, or throughout, Quaternary time, evidence for their recency of displacement commonly is incompletely preserved or equivocal.• In contrast, the State Mining and Geology Board, in their Policies and Criteria (adopted 21 November 1973), defined only those faults which have had surface displacement within Holocene time as ··active and hence as constituting a potential hazard."
l ln those cases where data are available from field and aerial pho1ographic investigations specifically directed at the problem of potential surface faulting, the potentially active fauhs shown on the special s1udies zones ffiaps may not be directly relatable to the entire Quaternary Period. For example. the "'recenlly active"' fault traces depicted on some U.S. Geological Survey maps are believed to be predominantly of la1e Quaternary age and may exclude most faults 1hat have become inactive during or prior 10 early Qualernary time.
GEOLOGIC AGE YEARS BEFORE
E<a Period Epoch
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QUAIERNARY ·u 0 Pltis1occnc· N 0 z w u
Plii.x:cnc TERTIARY
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200
11.000
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7.000.000 - 10.000.0-00-
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: ... t>00.000.000 r--
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F;autls along which movement h11s occurred duling lhis inlerv;al are delined M acrive bf Policies ;ind Crheria or the Slate Mining and Geolo9y Board. ·
Fauth defined iu po1~rially ai::li..-e lor lhe pur. pose of 6eline•ling speci11I sllJdies zc:nes.
Figure 2. Geologic time scale
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1971> FAULT HAZARD ZONES IN CALIFO •. <IA 7
Uses and Limitations of Special Studies Zones Maps
The special studies zones are delineated to define those areas within which special studies arc required prior lo building structures for human occupancy. Traces of potentially active faults arc shown on the maps mainly to justify the locations of zone boundaries. These fault traces are plotted as accurately as the
·sources of data permit; yet the plots are not sufficiently accurate to be used as the bases for set-back requirements, and they should not be so used.
The State Geologist has identified potentially active faults in a broad sense, and the evidence for potential activity of some faults may be only weak or indirect.
The fault information shown on the maps is not sufficient to meet the requiren1ent for special studies. Local govern1ncn1al units n1ust require the developer lo evaluate specific sites within the special studies zones to determine if a potential hazard from any fault, wheth~r
heretofore rccognizod or not. exists with regard to proa posed structures i\nd their occupants.
The surface fault ruptures associated with historic earthquake and creep events are identified where kno\vn. However, nu degree of relative potential for future surface displacement or degree of hazard is implied for the faults shown. Surface ruptures resulting from the secondary effects of seismic shaking during historic ti111c are 01nit1cd fronl the rnap und do nut serve as a basis fc>r zoning.
Model Ordinance and Code
In order to assist 1hc cities and the counties lo in1plement the Alquist-Priolo Act, a suggested Model Ordinance and Code \\.'as written by Jarnes E. Slosson, former State Geologist. This publication is available from the Division of Mines and Geology. P.O. Box 2980, Sacramenlo CA 95812, for 25 cents plus tax.
SUMMARY OF POLICIES AND. CRITERIA PURSUANT TO THE ACT
Policies and Criteria, called for in the Alquist-Priolo Act, were intially adop1ed on November 21, 1.973, by the Staie Mining and Geology Board following a review by all counties anc.I incorpora1ed cities in California. The Policies and Cri1eria were subsequently expanded and slightly revised July I. 1974. and June 26. 1975. Future revisions n1ay be anticipatcc.I in orc.lcr to assist the cities and counties in i1nplc111cnling the Act.
Table 2. A summary of policies and criteria adopted by the State Mining and Geology Board. Complete text is in Appendix 8.
PCJl.l(.IES
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REFERENCES
Arnold, R., 1918, Topography and fault system of the region of the San Jacinto earthquake: Seismol. Soc. America Bull., v. 8, pp. 68-73.
Bean. R.T., 1955, Publication of State Water Resources Board, Appendix B, Geology of San Jacinto and Elsinore Basins.
Bean, R.T., 1977, Personal communication.
Envicom Corporation, June 21, 1974, Preliminary geologic/seismic subsurface investigation, Soboba Properties, Inc., Soboba Springs, CA. unpublished report.
Fett, J.D., Hamilton, D.H., and Fleming, F.A., 1966, Continuing surface displacements along the Casa Loma and San Jacinto faults in San Jacinto Valley, Riverside County, California: Association of Engineering Geologists, Bulletin, v. no. 1. p. 22-32.
Fett, J.D., 1968, Geophysical investigation of the San Jacinto Valley, Riverside County, California:·· ·Univ. of Calif. masters thesis.
Friedman, M.E., Whitcomb, J.H., Allen, C.R., and Hileman, J.A., 1976, Seismicity of the southern California region, l Jan. 1972 to 31 Dec. 1974, Seismological Lab., California Inst .. of Technology, Pasadena, CA.
Hileman, J.A., Allen, C.R., and Nordquist, J.M., 1973, Seismicity of the southern California region, 1 Jan. 1932 to 31 Dec. 1972: Seismol. Lab., California Institute of Technology, Pasadena, California.
Jennings, C.W., 1975, Fault map of California with locations of volcanoes,. thermal springs, and thermal wells: California Division of Mines and Geology, scale 1:750,000.
Lamar, D.L., Merifield; P.M., and Proctor, R.J., 1973, Earthquake recurrence intervals on major faults in southern California, in Moran, D.E., and others, eds., 1973, Geology, seismicity and environmental impact: Assoc. of Engineering Geologists, Special Publication, p. 265-276.
Lofgren, G.E., 1976, Land Subsidence and aquifer-system compaction in the San Jacinto Valley, Riverside County, California--a progress report: U.S. Geological Survey, Journal of Research, v. 4, no. 1. p. 9-18.
Morton, D.M., and Gray, C.H., Jr., 1971, Geology of the northern peninsular ranges, southern California: Geologic guide and road log, in Elders, W.A., ed., 1971, Geological excursions in southern California: Geol. Soc. America, Cordilleran Sec. Mtg., Riverside, California, Univ. of Calif. Riverside, Campus Museum Contributions No. 1, p. 60-93.
i GARY S. RASMUSSEN & ASSOCIATES
National Aeronautics and Space Administration, March 30, infrared aerial photographs, Miss. 164, No. 3276, 3277:
1971, color 1:120,000.
Proctor, R.J., 1962, Geologic features of a section across the Casa Loma fault, exposed in an aqueduct trench near San Jacinto, California: Geol. Soc. America Bull., v. 73, p. 1293-1296.
Proctor, R.J., 1971, Personal conununication.
Proctor, R.J., 1974, New localities for fault creep in southern Calif. Raymond and Casa Loma faults (abs) Geol. Soc. America Abs. with Programs, p. 238.
Rasmussen, Gary S. & Associates, Iir.c., September 18, 1974, Subsurface engineering geology investigation for addition to Arroyo Fairways Mobilehome Club, northeast portion, Hemet, California, Project No. 1060, on file at our office.
Rasmussen, Gary S. & Associates, Inc., November 26, 1974, Subsurface engineering geology investigation for Lots 1-9, 15, 16, 19, 21-41 of" Tentative Tract 4271 and 31,i acres along Acacia Avenue, West of New Chicago Avenue, Hemet, California, Project No. 1076, on file at our office.
Rasmussen, Gary S. & Associates, Inc., February 12, 1975, Subsurface engineering geology investigation of Lots 1-4, & 7 of Tract No. 4635-1; plus approximately 27 acres at the northwest corner of Florida Ailenue and New Chicago Avenue, Hemet, California, Project No. 1086, on file with the County of Riverside.
Rasmussen, Gary S. & Associates, Inc., October 29, 1975, Engineering geology investigation of Tentative Tract 7102, Lots 1-9, Yale Street, South of Parkview Street, Hemet, CaHfornia, Project No. 1118, on file with the County of Riverside.
Rasmussen, Gary S. & Associates, Inc., May 10, 1977, Subsurface engineering geology investigation of 10-Acre Parcel, NE Corner of Devonshire Avenue and Yale Street, Hemet, California, Project No. 1192, on file at our office.
Rasmussen, Gary S. & Associates, ITic., May 10, 1977, Subsurface engineering geology investigation of a 5-Acre Parcel, SE Corner of Devonshire Avenue and Yale Street, Hemet, California, Project No. 1196, on file at our office.
Rasmussen, Gary S. & Associates, Inc., May 10, 1977, Subsurface engineering geology investigation of a 5-Acre Parcel, East of Yale, between Devonshire Avenue and Florida Avenue, Hemet, California, Project No. 1197, on file at our office.
Rasmussen, Gary S. & Associates, Inc., April 7, 12, 1978, Alquist-Priolo Special Studies Zone along NE side of Park Hill, Hemet, California, Project No. 1307, 1307-2, on file with the County of Riverside and the State of California.
ii GA.RYS. RASMUSSEN & ASScx:::IATES
Rasmussen, Gary S. & Associates, Inc., January 16, 1979, Subsurface engineering geology investigation of an Irregular 13.4-Acre Parcel, NW Corner of Menlo Avenue and Park Avenue, Hemet, California, Project No. 1428, on file with the County of Riverside.
Riverside County Flood Control and Water Conservation District, December 20, 1972, Aerial photographs 33, 34, and 35, Sea.le 1"=1000 1 •
Riverside County Seismic Safety Element to the General Plan, September 1976.
Rogers, T.H., 1966, Geologic map of California, Olaf P. Jenkins edition, Santa Ana Sheet: California Division of Mines and Geology.
Rolfe, F., and Strong, A.M., 1918, The earthquake of April 21, 1918, in the San Jacinto Mountains: Seismal. Soc. America Bull. v. 8, p. 63-67.
Schnabel, P.B., and" Seed, H.B.", 1973, Accelerations in rock for earthquakes in the western United States: Seismol. Soc. America Bull. v. 63, no. 2.
Sharp, R.V., 1967, San Jacinto fault zone in the Peninsular Ranges of southern California: Geological Society of America Bulletin, v. 78, p. 705-7 30.
Sharp, R.V., 1972, Map showing recently active breaks along the San . Jacinto fault zone between the San Bernardino area and Borrego Valley, California: U.S. Geological Survey Misc. Investigations Map I-675, 1:24,000.
Sharp, R.V., 1975, En echelon fault patterns of the San Jacinto fault zone, in Crowell, J.C., ed., 1975, San Andreas fault in southern Calif.,
- a guide-to San Andreas fault from Mexico to Carrizo Plain: California Division of _Mines and Geology, Special Report 118, p. 147-152.
Slemmons, D.B., 1977, in the United States: Report 6.
State-of-the-art for assessing earthquake hazards U.S. Army Engineer Waterways Experiment Station,
Thatcher, W.J., Hileman, J.A., and Hanks, T.C., 1975, Seismic slip dislocations along the San Jacinto fault zone, southern Calif. and its implications: Geological Society of America Bulletin 86, p. 1140-1146.
Townley, S.D., 1918, The San Jacinto earthquake of April 21, 1918: Seismol. Society of America Bulletin, v. 8, p. 45-62.
Waring, G.A., 1919, Ground water in the San Jacinto and Temecula Basins, California: U.S. ·Geological Survery Water Supply Paper 429.
iii GARY 9. RASMUSSEN & ASSOCIATES
EXPLANATION OF LOG ABBREVIATIONS
brn .•..•..... brown bdng ....•..•. bedding bldr ......... boulder c ............ coarse cbls .•....... cobbles drk •••....... dark f .....•...... fine gr .......•... granitic gm .......... green grad ......... gradational grvl ...•..... gravel gry .• : ....... gray j ............ jointing lam .......... laminar lt .......•... light m ............ medium meta ......... metamorphic
. p.cons ..... ,.poorly consolidated pbls ......... pebbles Pot SS ...•... Potato Sandstone sd ........... sand v ........•... very w/ ........... with w. cons ...... well consolidated yel .......... yellow occ ........... occasional
GARY S. RASMUSSEN & ASSOCIATES
NllE
ISO
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bfn'd in~ trench
Horizontal scale 1"•10'
Vertical scale
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IO
450
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trench
ENCLOSURE 5
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GARY S. RASMUSSEN & ASSOCIATES, INC. Howard Rose Co.-Girard I; Devonshire-Hemet Project No. 1443
5
10
Horizontal scale 1''=10 1
Vertical scale l"=S'