DARWIN MYERS ASSOCIATES

ENVIRONMENTAL RCSCARCH • ENtilNl::F-HIN(; (i!=()I ()(.iy

19 September 1989

Mr. Glenn Craft 620A 29th Street San Francisco CA 94131

Subject:

Dear Mr. Craft:

Addendum Subdivision 5496 3156 7Jrd. Avenue Oakland, California DMA Project 2002.89

On 18 September, we received a copy of a letter issued by Geo/ Resource Consultants, Inc. (dated 12 September 1989). The GRC letter, copy of which is attached, reviewed our report for the City of Oakland. The primary conclusion of the GRC letter is that our report is adequate. However, GRC had five comments/questions that required clarification. The following is a point-by-point response to those comments/questions.

1. The Soares & Associates report was issued in 1987. A com­plete bibliographic citation is presented on page 14 of our report.

2. We were provided with rough field logs of the three boreholes logged by Alan Kropp & Associates. Copies of the field logs are presented herein (see Appendix A). The location of each borehole is shown in Figure 9 of our 23 May 1989 report.

3. The bibliographic citation to the "Fault Evaluation Report, Oakland East Quadrangle" presented on page 13 of our 23 May 1989 report is incorrect. The correct citation is as follows.

Smith, T.C., 1980 1 "Fault Evaluation Report 102 - Oakland East Quadrangle", California Division of Mines and Geology, unpublished.

4. The GRC comment indicated that Figure 6 of our report lacked a scale, north arrow, and the explanation was incomplete. These deficiences were corrected (see attached Figure 6).

1 JOK PINE STREU • MAR l INLL, CA 94553 • 4151370-9330

5, We concur with the comment of GRC regarding Figure 9. It shows a shaded area in the northeast portion of the site labeled "permitted building area". The remainder of the site is considered to be in the restricted building zone, including the cut slope overlooking 73rd. Avenue (see attached Figure 9).

Sincerely,

DARWIN MYERS ASSOCIATES

Darwin Myers, C.E.G. 946 Principal

cc: Mr. Tim Low (3) Off ice of Public Works city of Oakland

Ms. Lisa Dirth Geo/Resource Consultants, Inc.

2 (IP.!\, DARWIN MYERS AssOCIATES '-..... ··' -· ,~,,

·· ..

z Q r-< > w -" w

0 2511

SCALE

-----~

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.----~'---------- ,.,

HAYWARD FAULT PLAN( 310

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The loc;;:itions a~ liniita-t ions of tl'ie geolo~ic fei'.ltures shown on this l'll<.1p tire accurf!te representi:i­tio~s of said 1eatures es they exist on the groundi 1.1ere platc..'CI on this IMP by mt, or under rny supervis­ion, and are acc:1,.1r1;3tt:! to th~ best of my knowt~dge.

Signed:

t.lunber:

B-3 • ....... .......

Bor·ihg lo99L-d by Alan Kropp & A£soc\ates (9·6·88)

G0ologic Contact

~ [xploratory Trench

'Active Fault Trace

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SITE GEOLOGIC MAP ""'"''6 Darwin Myers Associates D"'-1 L 5-23-89 JOllNiJM!ll'-! 2002.89

The locations ar1d linritations of the ge(:log\c fea~ures ~hown on this m.::ip a1-c accurate r~rest'r1tlltions of ssid fe;;:iturcs as they ~xist on the sro:..ino'; were plac(' on this map by me, cw undtr my ~upervision, and are accurate to the best of my kno"l~dge.

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~ FAULT EVALUATION MAP ~ .... ---~~-~----1 "' SCALE 1' ..= 2 5 / FIGURE.

9 D ... Tl 5-23-89

Darwin Myers Associates

2002.89

LOGO•O IV 8L_

O~H ORILClO '1- (,, .. n:-;-DESCRIPTION ANO CLASSIFICATION

ALAN KROPP & ASSOCIATES

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SlATE OF CALIFORNIA-THE RESOURCES AGfNCY

DEPARTMENT OF CONSERVATION

DIVISION OF MINES AND GEOLOGY &A Y AREA REGIONAL OFF~CE

380 CIVIC DRIVE. SUITE 100 PLEASANT HILL, CA 9....,23-1997 PHONE, (• 1 ') />40.5920

A TSS 599-,920

Mr. Randall A. Lum Deputy Director Development Services City of Oakland one City Hall Plaza Oakland, CA 94612

Dear Mr. Lum:

GEORGE DEUKMEJlAN, GQ~r

December 13, 1989

we are placing on open file the following report, reviewed and approved by the City of Oakland in compliance with the Alquist­Priolo Special Studies Zones Act:

Fault hazard investigation, subdivision 5496, 3156 73rd Ave., Oakland, CA; by Darwin Myers Assoc.; 5/23/89; with addendum of 9/19/89.

EWH:hrk /

cc: A-P file'

Sincerely,

EARL W. HART, CEG 935 Senior Geologist &

Program Manager

CITY OF OAKLAND

CITY HALL• ONE CITY HALL PLAZA,• OAKLAND, CALIFORNIA 94612

Office of Public Works T TY 839-6451

State of California Department of Conaervation Diviaion of Mines & Geology 380 Civic Drl.ve, Suite 100 Pleasant Hill, CA 94523-1997

Attention: Mr, Earl W. Hart

December 8, 1989

RE: Geologic Report for State Geologist's Open File

Gentlemen:

Pursuant to the requirements of the Alquist-Priolo Special. Studle~ Zones Act, the following Geologic Report and review are submitted herewith for· inclusion in the Statce Geologist's Open File;

"Fault Hazards lnvestigation, 3156 - 7~rd Avenue, Oakland, Ca."

If there are any questions regarding this report, please t•ontuat. Timothy Low at (415) 273-2259 between 1:00 P,M, to 4:00 P.M. any weekday,

TL:da.i

Enclosure

Very truly yours,

TERJ/.Y E. ROBERTS ((==och RANDAL], A, LUM Deputy Director Development Services

2. , Geo/Resource Consultants, Inc. 13EOL.OGISTS J ENGINEERS I ENVIRONMENT AL SCIENTISTS

October 11, 1989 1517-00-0

Mr. Tim Low City of Oakland Office of Public Works Development Services Department One City Hall Plaza Oakland, CA 94612

OOAPOAATE HEAOOUAATEFIS; Sl)1 HARFUSON STREET SAN FRANCISCO, CA 94i07 TEl.EP"ION!i: (41?) 777,3177 FACSIMILE (4151 777-5623

RE: REVIEW OF ADDENDUM TO FAULT HAZARD INVESTIGATION SUBDIVISION 5496, 3156 73RD AVENUE, OAKLAND, CA PREPARED BY DARWIN MYERS ASSOCIATES

Dear Mr. Low:

ACa10NAL OFFICES: SAN FRANCISCO SEATTLE TUCSON/PHOENIX WASHINGTON, C.C.

We are in receipt of the above referenced addendum, dated September 19, 1989. This addendum is in response to comments in our letter review dated September 12, 1989. We have reviewed this document as required by the Oakland Municipal Code, Article 8, Section 2-8.06, for sites located within the Alguist-Priolo Special Studies Zone. Our review was solely for the purpose of evaluating the adequacy of the investigation for assessment of surface fault rupture potential.

During our review of this addendum we found that all items Of concern had been modified or corrected. After our review of the original report, conversations with Mr. Darwin Myers, and review of the addendum letter, it is our opinion that the Fault Hazard Investigation, dated May 23, 1989, together with the above described addendum, dated September 19, 1989, adequately assesses the fault rupture potential for the proposed subdivision and construction of two single family residences for the property described as Subdivision 5496, 3156 73rd Avenue, Oakland, prepared by Darwin Myers Associates. However, the initially proposed dwelling sites will have to be relocated to comply with the setback (restricted building zone) specified by the geologist. In addition, the plans should be. checked by either the City of Oakland or Darwin Myers to ensure that they comply with the setback delineated by Darwin Myers Associates.

In order for the report covering this property to be complete, it must include the original report, the addendum letter, the accompanying modified figures (Figure 6 and Figure 9) and the boring logs by Alan Kropp & Associates. The addendum was submitted directly to us by the geologist for our review, so we are forwarding a copy of that document with the original report

220W: 1517-2

October 11, 1989 1517-00-0 Page 2

for your files. If additional copies are needed, it will be necessary for you to contact the owner or Darwin Myers Associates.

If you have any questions regarding the report or our review, please call.

Very truly yours, GEO/RESOURCE CONSULTANTS, INC.

~J_{)~ ElizabE\th S. Dirth, C.E.G. 1240 Senior Engineering Geologist

A~ LJ_ MH'-'-;. .,.....___ Alan D. Tryhorn1 .E.G. 1019 Senior Vice President

ESD/ADT:mb

xc: Darwin Myers Associates

220W: 1517-2 Geo/ Resource Consultants, Inc.

,.

September 12, 1989 1517-00-0

City of Oakland Off ice of Public works Development Services Department One City Hall Plaza Oakland, CA 94612

(;(/Hf'()kAt,: H~Al)(JIJAl-ll~i-IS

8bl HAR~~ISON S"Tflt:~l SA~ FRANCISCO. CA 9"107 1'£·\ £P1~0Nf (.4151777-3177 FACSIMILE ~~15) 771"·t,fj7:'.

RE: REVIEW OF FAULT HAZARD INVESTIGATION SUBDIVISION 5496, 3156 73RD AVENUE, OAKLAND, CA PREPARED BY DARWIN MYERS ASSOCIATES

Attn: Mr. Tim Low

Dear Mr. Low:

REGIONAL C>Ff 1S[~, S.'.N FR.A.NCISCO 5E:.ATILE TUGSO~rP+-iOFNI)(

WA~HINC3TON, D.G

We are in receipt of the above referenced report, dated May 23, 1989. We have reviewed this document as required by the Oakland Municipal Code, Article 8, Section 2-8 .06, for sites located within the Alquist-Priolo Special Studies Zone. Our review is solely for the purpose of assessing the adequacy of the investigation for surface fault rupture potential.

The subject property is an approximately square lot situated on the northeast side of 73rd Avenue, approximately 120 feet southeast of Sunkist Drive. We understand that the current development plan is a subdivision of the lot into two parcels and construction of two single family residential structures. 'l'he upper or northeastern portion of the lot is relatively flat. The southwest half of the lot consists of a steep southwest facing slope with a maximum gradient of approximately 100% or 1:1 (horizontal:vertical). Total topographic relief is approximately 40 feet.

Darwin Myers Associates (DMA) investigated this site to evaluate the possible hazard of fault offset through the site. Their evaluation was based on 1) previous investigations in the nearby vicinity, including both published and unpublished reports and maps, 2) examination of aerial photographs / 3) a site reconnaissance, and 4) excavation and logging of three exploratory back.hoe trenches totalling 140 feet in length.

During DMA' s investigation, they observed and described three locations of shears in the exploratory trenches. The evidence of active faulting was described as •steps• in the topsoil/bedrock contact associated with a clayey shear plane. Therefore, DMA

218W: 1517-1

~eptember 12, 1989 1517-00-0 Page 2

concluded that an active trace of the Hayward fault passes through the western portion of the site. They further stated that it is likely that additional traces are p:i;esent in the slope at the southwestern edge of the property or under the 73rd Avenue right-of-way. OMA further concluded that the property would undergo "violent" ground shaking during a high magnitude earthquake on the Hayward fault, Since the presence of active faulting was noted in the subsurface, OMA recommended a 25-foot setback (restricted building) zone from what was described as the east boundary of the fault zone. However, they stated that it would be possible to construct buildings not for human habitation, such as garages, within this zone with the caveat that these improvements would be subject to damage or total destruction in the event of fault movement.

Geo/Resource Consul tan ts, Inc, ( GRC) performed a review of the subject report. Our evaluation was based on a thorough examination of pertinent publications and documents, including unpublished reports in our files, review of aerial photographs of the site and vicinity, a brief site reconnaissance, and observation of the exploratory trenches.

We feel the investigation adequately assesses the potential for surface fault rupture. In addition, we concur that the 25-foot setback delineated on Figure 9 of the subject report is appropriate. However, there are a few minor items that need to be corrected to make the report complete and accurate. These items are described as follows:

1) The reference to the report by Soares & Associates on page 6 cites a date of 1878. We believe that date to be incorrect.

2) Work by Alan Kropp & Associates report completed in 1988 is referred to in the text. Information from the boring logs in that report are paraphrased in DMA's report. We feel the boring logs should be included as figures or an appendix.

3) we believe the first reference in the Bibliography is incorrect and actually refers to Smith, T.C., 1980, Fault Evaluation Report 102, Oakland East Quadrangle: California Division of Mines & Geology, unpublished. This should be corrected.

4) Figure 6 contains no north arrow or scale and the street is unlabeled. These should be included. In addition, the legend is incomplete. The borings, contacts, and trenches have not been included

5) We feel that the restricted building zone as depicted in the Fault Evaluation Map, Figure 9, should extend down to the street and not end at the top of bank as shown on this map.

218W: 1517-1 Geo/ Resource Consultants, Inc.

peptember 12, 1989 1517-00-0 Page 3

Based on our review and our observations of the excavated trenches, it is our opinion that the Fault Hazard lnvestigation, by Darwin Myers Associates, dated May 23,, 1989, adequately assesses the fault rupture potential for development of the property described in this report as Subdivision 5496, 3156 73rd Avenue, However, we have withheld our approval pending the correction of the minor i terns described above. When we have received a revised report or addendum that addresses these items, we will complete our review. In addition, we feel that DMA should review a final development plan delineating the setback to assure that it has been properly placed.

If you have any questions regarding the report or our review, please call.

Very truly yours, GEO/RESOURCE CONSULTANTS, INC.

L:{~L_;J_ {)~~ Elizabeth S. Dirth, C.E.G. 1240 Senior Engineering Geologist

.~~~/)-~. /Ala~ D. Tryh¢;cr\, C.E.G. 1019 Senior Vice President

xc: Darwin Myers Associates

21BW: 1517-1 Geo/ Resource Consultants, Inc.

I I I I I FhUi.:..T HAZARD INVESTIGATION

SUBDIVISION 5496

I 3156 73RD AVENUE

OAKLAND, CALIFORNIA Dl{A PR0:11:c1' 2002. 89

I I I I I I I I I I MAY 1989

I I I rfl;!f li<,. DARWIN MYERS ASSOCIATES

··-· ....... ;----------

I I I I I I I I I I I I I I I I I I I

DARWIN MYERS ASSOCIATES

ENVIROf\IMF:N r Al AF.SEARCH • EN(ilN(.:i-:AING GEOLOGY

23 May 1989

Mr. Glenn Craft 620 A 29th Street San Francisco CA 94131

Subject:

Dear Mr. Craft:

Fault Hazard Investigation Subdivision 5496 3156 73rd Avenue Oakland, California OMA Project 2002.89

We are enclosing six (6) copies of the above captioned report, which have been prepared at your request. since this property is located within the Alquist-Priolo Special studies Zone, and consequently will be subject to review by a registered geologist acting in behalf of the City of Oakland, it should be submitted to them early in the building permit process. We are also sending a copy of the report to Alan Kropp & Associates.

Should you have any questions concerning this report, or reqi.1ire further assistance, please call.

Sincerely,

DARWIN MYERS ASSOCIATES

k"""""-~~' Darwin Myers, CEG 946 Principal

enclosures

IJOH PINES I RFFT • MARTINEZ. CA 94553 • 415/370 cJ:l:lO

I I I I I I I I I I I I I I I I I I I

INTRODUC'.rl ON

This report presents the results of a fault hazard investiga­tion of a 0.39 acre property that is designated "single farni.ly residential''. The property fronts on the east side of 73rd Avenue, approximately 125 feet south of the Simson Street intersection (see Figure 1). The site is within an estab­lished residential neighborhood, and there is the shell of a small residence on the property, along with ornamental vegeta­tion.

The parcel was created prior tc enactment of the Alguist­Priolo Special Studies Zone Act. Nevertheless, the City of Oakland has determined that the project requires a fault haz­ard investigation prior to issuance of construction permits.

Site Description

The property is located on a so:..ithwest-facing hillside. Tra.­ditionally, geologists have interpreted the rolling, hummocky topography in this hillside area to be a possible errodcd fault scarp.

Elevations range from +312 feet to less than +275 feet. Natu­ral slopes in the central and northeast portions of the site arc less than 10%. The southwest portion of the property is an existing cut slope, which overlooks 73rd Avenue. It is approximately 20 feet high and possesses a slope gradient of 100%+.

Purpose

The site is located within the Alguist-Priolo Special Studies Zone that encompasses recently active and potentially active traces of the Hayward fault. This law (California Public Resources Code, Division 2, Chapter 7.5, commencing with Sec­tion 2621) requires a geologic investigation directed to the hazard of surface fault rupture for all subdivisions of land, and for most types of new construction, including construction of a single-family residence on a lot of record, if there is a known fault trace within 100 feet of the property. Further­more, the law states that structures for human occupancy can­not be built astride the trace of an active fault. Therefore, in compliance with the state and local regulations, the pur­pose of this investigation was to evaluate the possible hazard of fault offset through the site.

Scope

The scope of woJ.-k to be perforrn<?d in this investigation included: 1) review of relevant published materials, 2) review of previous consultants' work in the area, 3) exami­nation of aerial photographs, 4) a site reconnaissance, 5) one

ij/llit .. , DARWIN MYERS AssOCIATES --·--··· '~i

I I I I I I I I I I I I I I I I I I I

full day of exploratory trenching, 6) geologic evaluation of the data gathered, and 7) preparation of this report.

This report is subject to review by the City of Berkeley. Although we strive to meet city requirements for such studies, we cannot guarantee that no additional geologic work will be required.

METHODS OF INVESTIGATION

Review of Existing Published Data

A variety of published sources were reviewed to obtain an overview of the geologic and seismic setting of the subject parcel. These sources included geologic literature, and reports and maps published by local, state and federal agen­cies. The most significant of these sources are the Special Studies Zones Map prepared by the California Division of Mines and Geology (CDMG, 1982), a Fault Evaluation Report prepared by the CDMG, fault trace maps prepared by the U.S. Geological survey (Radbruch-Hall, 1974 and Herd, 1978), a general purpose geologic map of the Oakland East Quadrangle (Radbruch, 1969), and an earthquake epicenter map (Scheimer and Mills, 1984). Detailed citations for these reports are included in the bib­liography.

Review of Consultant-Prepared Reports

Alquist-Priolo reports submitted to the City of Oakland for nearby projects were reviewed to obtain site-specific informa­tion on the location of fault traces in the general vicinity. Additionally, Alan Kropp & Associates logged three exploratory borings on the site in 1988. Review of these reports and logs was included in our analysis.

Examinati.on of Aerial Photographs

One (1) set of vertical-angle aerial photographs was examined using a mirror stereoscope equipped with 3X and 8X binoculars. Aerials provide a means of observing large-scale, subtle fea­tures that, in the field, may appear isolated and inconsequen­tial. With this overview, a systematic pattern of linear fea­tures may be observed, which collectively provide insight into the location of geologically recent fault traces. The pho­tographs examined were flown in 1939 at a scale of 1:20,000. More detailed citations of the photos are presented in the bibliography.

Surf ace Reconnaissance

A surf ace reconnaissance of the site and surrounding proper­ties was performed on 1 May 1989 to determine if possible dis-

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tress 01 distortion features were present that might be related to tectonic creep.

Exploratory Trenching

Three exploratory trenches were logged. They averaged 7 to 8 feet in depth and had an aggregate length of l40 feet. They were oriented northeast-southwest, approximately perpendicular to the general trend of the Hayward fault. The int<ent of the trenches were to "shadow" the potential building site and adjacent area. (The term "shadow", as used herein, implies that a fault w.ith the general trend of the Hayward fault could not cross the building sites without also crossing the exploratory trench.) The locations of the exploratory trenches shown in Figure 6 was established taping from known physical features (chiefly fence lines and property corners).

The excavation work was performed with a rubber-tired excava­tor equipped with a 24-inch bucket. The south wall of the trench was cleaned in a grid pattern, exposing a continuous horizontal swath of soils, colluviwn and weathered gabbro bedrock. Material smeared by the excavation bucket was also removed in vertical swaths every five (5) feet. Where soils were exposed, and all areas where geologic contracts and weathering-related profiles were exposed the trench was cleaned for continuous tracing of such contacts.

An accurate profile was prepared utilizing a hand level and tape; geologic contacts and structural features were observed, geologic units were described, and a log was prepared that showed the details of observed features and conditions. Groundwater was not encountered and the walls showed no ten­dency to collapse.

GEOLOGIC AND SEJSMIC SETTING

Historic Perspective

The Hayward tault zone comprises a northwest-trending zone of faults along the western front of the hills bordering the east side of San Francisco Bay. The fault zone can be traced nearly continuously northwestward from the Warm Springs dis­trict in Southern Alameda County to San Pablo Bay at Point Pinole in Contra Costa County. It cannot be traced south of Warm Springs with any degree of certainty. East of the San Francisco Bay area, the Hayward fault is inferred to merge with the Calaveras fault in the vicinity of the Calaveras Reservoir.

Movement along fault.s within thi.s zone has caused ~wo major historic e~rthquakes, one in 1836 and one in 1868. Rupture surfaces were opened between San Pablo and Mission San Jose in 1836; and between Mills College, Oakland and Warm Springs in

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1868. Faulting was reported as far north as the University of California, Berkeley, in the 1868 quake.

Tectonic creep was first recognized on the Hayward fault in 1966, and since then has been observed at various places along its length from San pablo to Fremont. It has cracked and off­set curbs, streets, fences, railroad tracks, pipelines and buildings. All creep movement appears to be right-lateral.

Traces within the zone of faulting are, in some places, clearly delineated by physiographic features such as sag ponds, trenches, scarps and offsets. In other places such evidence is very faint, even in areas where we know from his­toric records that surface faulting took place.

A review of existing seismic records provides compelling evi­dence that the Hayward fault is seismically active. For exam­ple, the earthquake epicenters recorded by the U.S. Geological Survey during the period 1969 through mid-1982 show a good correlation between earthquake epicenters and known active faults, in<;luding the Hayward fault (see Figure 2) . These epicenters are evidence of adjustments taking place at depth along active Bay Area faults. In a typical year, 20 or more seismic events are recorded by the USGS in the immediate vicinity of the Hayward fault.

Geologic Mapping

The most recent bedrock geologic maps of the Oakland East Quadrangle is that of the USGS (Radbruch, 1969). To enhance readability, this map has been photographically enlarged from its i;mblished scale of 1"=2000' to 1"=1000' (see Figure 3). This map is based chiefly on field geologic mapping of bedrock outcrops, and review of information in City files, including H~port~'d landsl:i.des and soils reports for land development projects.

According to Figure 3 the Hayward fault is composed of a net­work of interconnected and branching fault traces that gener­ally trend in a northwest direction. Each fault trace is rep­resented by a dashed line, indicating that the locations shown are inferred. 'I'he fault traces are distributed across a zone that is 2500 to 4000 feet wide. 'I'he site is in the center of the fault zone, and one trace of the Hayward fault is mapped through the site.

'I'he site and vicinity are mantled by undivided Quaternary deposits (Qu). The nearest bedrock outcrop occurs 700 feet south of the site. It is an exposure of serpentine (sp). Leona Rhyolite (Tl) and Franciscan gabbro (gb) are mapped 1500 and 2000 feet southeast of the site, respectively.

It should be emphasized that the Radbruch map does not clas­sify faults by activity status, and the purposes of the map

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were not aimed at accurately defining the location of the Hay­ward fault. The available outcrop data does not constrain the location of fault (i.e. there are no outcrops that straddle the fault trace). Moreover, the map does not cite any fault­related geomorphic features in the vicinity of the site.

FAULT TRACE MAPS

The USGS has published an annotated map showing lineaments that are interpreted as possible evidence of Quaternary fault traces (Herd, 1978). It is based on interpretation of 1939 photographs, which predated at least some of the development along the Hayward fault zone. Herd indicates that fault­related features have been overwhelmed by landsliding in por­tions of the Oakland Hills (see Figure 4). The map indicates that the nearest photolineament is approximately 2000 feet northwest of the site.

To the south of the site, Herd maps a fault trace through the vicinity of the Holy Redeemer College. (This feature is more than one mile southeast of the property.) Herd also shows a scarp coincident with the I-580 alignment, approximately 1400 feet northeast of the site. This feature is represented by a dolled, queried line, indicating that the features seen arc discontinuous and may be an explanation other than faulting.

The lack of a lineament in the vicinity of the site does not prove the property is free of evidence of faulting. It does indicate that fault traces, if they are present, are subtle. Geomorphic features indicative of active faulting (if they exist), have been obscured by erosion, sedimentation, vegeta­tion and/or the acts of man.

Af,QUIST-PRIOLO ACT

Special Studies Zone

One of the provisions of the Alquist-Priolo Act directs the State Geologist to prepare Special Studies Zone (SSZ) maps for each of the faults considered to be active a.nd sufficiently well defined. On 1 July 1974, the Oakland East Quadrangle ssz map was issued; it was revised on 1 January 1982 (see Figure 5). The boundary of the SSZ is represented by solid black lines connected by encircled "turning points". The area within the SSZ is represented by a shaded pattern.

The location of the fault traces shown on the map are inferred. They are based primarily on reconnaissance-level data that is variable in quality. These traces were used to define the width and trend of the SSZ. However, the legend of the official map states that recently active traces of the Hayward fault may exist anywhere in the SSZ. According to

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this map, the property is on the central portion of the ssz, which is nearly 2000 feet wide in the vicinity of the site. The fault traces shown on the ssz map are represented by short dashes with queries, indicating the location is inferred and highly speculative. According to Figure 5, a queried fault trace is mapped through the immediate vicinity of the site. The trace has a mapped length of 0.5 miles.

Previous Investigations

The purpose of the Special Studies Zones (SSZ) maps is to ensure that development in proximity to known active faults gives adequate consideration to the hazard of surface fault rupture. The reports must be prepared by a geologist regis­tered in the State of California Moreover, the local juris­diction is required to provide peer review of the report, per­formed by a registered geologist. Copies of all consultant­preparcd reports, along with evidence of peer review, must be sent to the California Division of Mines and Geology. This requirement provides the CDMG with a basis for modifying the boundary of the ssz, as detailed studies define the precise location of the fault.

As part of our investigation, we reviewed the CDMG files of consultant-prepared reports. There is no record of previous investigations in proximity to the site. The nearest study areas were approximately 1500 feet from the site and provided no useful data. For that reason they arc only briefly summa­rized herein. The location of the geologist's study areas are identified in Figure 5.

§ttl!"J:_( '.!Jl81). The scope of the investigation included the logging of an 85-foot long trench that was oriented generally east-west, and it ranged from 5.5 to 10.5 feet in depth. The trench log indicates topsoil overlying weakly consolidated sedimentary deposits (older alluvium). The bedrock was ti.1 ted (bedding Nl0W,350W), but no evidence of faulting was reported.

Garbe ( 1987). This investigation i.ncluded the excavation and logging of an exploratory trench 166 feet long and 6 to 8 feet in depth. The trench penetrated undivided Quaternary deposits that were tilted (bedding N46-50W,6°swJ. The primary conclu­sion of the report is that the Garbe study area is free of evidence of active faulting.

Soares & Associates (1878). The consultant's scope of work included the logging of an exploratory trench that was 116 feet long and ranged from 10.5 to 13.5 feet in depth. It pen­etrated Quaternary alluvial deposits rich in rhyolite detri­tus. No fault-related features were observed by the geolo­gist, and the primary conclusion of the report is that the site is free of evidence of active faulting.

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SITE INVESTIGATION

Alan Kropp & Associates

In 1988, Alan Kropp & Associates (AKA) logged three (3) exploratory borings (see Figure 6 for location of boreholes). The borehole logs indicate the following:

Boring B-1 was 10.5 feet deep. It penetrated colluvium to depth of 6 feet. Below that depth the field log indicates medium-grained sandstone that was severely weathered and highly fractured. This material may be weathered gabbro.

Boring B-2 was 16.5 feet deep. It penetrated colluvial deposits that are described as a sandy and clayey with abun­dant rock fragments.

Boring B-3 was 22.5 feet deep. The field log describes the upper 5 feet as sand (severely weathered ga~bro?). The field description of the remainder of the boring is consistent with weathered gabbro.

Photointerpretation

Our task for this phase of the investigation was twofold:

1. Determine if photolineaments cross the site, or if they can be projected through the site.

2. Examine the alignment of the fault trace originally mapped by Radbruch and subsequently endorsed, with modification, by the ssz map.

Because geomorphic f ea tu res character is tic of active fault i.ng are delicate and ephemeral and can be obscured or obliterated by vegetation, grading and development; we analyzed 1939 aerial photographs. Unfortunately, even in 1939 the hillside neighborhood that includes the site was established. If lin­eaments were present they were obscured by grading, construc­tion, landscape plantings and irrigation. Geomorphic features characteristic of active faulting were not associated with the fault trace shown on the SSZ map. There is a break in slope, (steeper to the east), but it is not straight and smooth. Features such as a break in slope are not direct evidence of faulting.

Site Reconnaissance

On 1 May 1988, we performed a reconnaissance of the site and surroundi.ng neighborhood. The cut slope on the southwest side of the property exposed severely weathered Franciscan gabbro in the central and southern segments of the slope; the north­ern segment is covered with vegetation (see Figure 7 Top). Gabbro is also exposed on the extension of the cut slope north

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of the site (i.e. on the Jackson Institution Baptist Church property, approximately 40 feet north of the site).

No evidence of tectonic creep features were observed on the perimeter streets (73rd Avenue and Sunkist Drive). The church building north of the site exhibited some evidence of dis­tress, but the sense of movement was not right-lateral, and the parking lot lacked evidence of a systematic pattern of aligned features.

Exploratory Trenches

The location of the three trenches is shown in Figure 6, Site Geologic Map. Logs of the trenches are presented in Figure 8 at a scale of 1" 005'. Trenches T-1 and T-2 provide a basis for tracing the east boundary of the fault zone across the site, and Trench T-3 shadows the eastern portion of the property.

Trench T-1. This trench penetrated a massive, clayey collu­vial deposit, with an old channel fill at the extreme east end of the trench. Steep, discontinuous partings were observed between Station 0+00 and 0+12; at Station 0+15 a shear plane juxtaposed cobble of conglomerate with a wedge of yellowish­brown clayey sand. This shear could not be traced to the floor of the trench, nor was it identified on the north wall.

Trench T-2. This trench penetrated a topsoil layer overlying severely weathered gabbro, which is a mafic intrusive rock within the Franciscan Assemblage. The gabbro was so thor­oughly decomposed in segments of the trench that it had the appearance of a salt-and-pepper sandstone. The chief mineral constituents of the gabbro are calcic plagioclase and mafic minerals (augite and probably hypersthene and olivcne). The decomposition appears to be the result of chemical weathering of the feldspars along joint planes. The weathering is so complete that the joints are no longer recognizable, although some blocks of moderately weathered gabbro remain in areas where the joints were more widely spaced.

Th"' most significant features seen in T-2 are the "steps" in the topsoil/bedrock contact (east side up). These "steps" occur at Station 0+22 and 0+36. In each case a northwest­trending shear zone is associated with these "steps". The shear plane at Station 0+22 was characterized by the presence of roots on both walls. The "step" at 0+36 was associated with a clayey shear plane that dipped to the southwest at 70 degrees. Figure 7 (bottom) shows a view of the "step" in top­soil at Station 0+36. The bedrock offset is nearly 1 foot at this locality.

Trench T-3. This trench penetrated unfaulted colluvial deposits, with a channel deposit at the cast end of the trench. This trench was very similar to T-1, except that is contained fewer (and smaller) pebbles.

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EVALUATIONS ANO CONCLUSIONS

The two principal hazards we have evaluated a.re: 1) surface fault rupture, and 2) groundshaking. Each of these hazards is discussed below.

1. Surface Fault Rupture

Surface rupture occurs when fault displacement extends toward and intersects the ground surface. Fault movement studies reveal that displacement occurs in two ways: 1) sudden displacement, and 2) fault creep. The first and better known type is the sudden displacement of the ground along a fault during an earthquake. Surface displacement does not occur every time an earthquake takes place. In California, surface faulting is typically associated with earthquakes possessing Richter magnitudes of approximately 6.0, or greater. When surface rupture occurs, the length and width of the rupture zone, along with the amount of relative surface displacement between opposite sides of the fault, can be highly variable. Further, faults which are capable of sudden displacements in excess of several inches often have smaller branch faults which diverge from the main fault trace. Secondary faults not directly or obviously connected to the main fault trace may exist, although these secondary faults are usually lo­cated within a few hundred yards of the main trace.

Based on data gathered during our investigation, an active trace of the Hayward fault passes through the western portion of the site. There is a break-in-slope coincident with the west boundary of the site. lt is likely that additional fault traces are present on the existing cut slope, or in the 73rd Avenue right-of-way. For that reason, it is our opinion that Trenches T-1 and T-2 only establish the east boundary of the fault zone.

Figure 9, Fault Evaluation map, shows our interpretation of site conditions, including the location of the east boundary of the fault zone. Most geologists agree that the greatest risk of damage from surface fault rupture is along existing fault planes in an active fault zone. These fault planes represent existing planes of weakness within the earth's crust. As stress builds up again, it is very likely that future movement will occur along the existing fault planes. The j.'ntent of setbacks is to provide a safety factor. Du.r­ing future earthquakes, the zone of faulting and deformation may not be restricted to the existing fault zone. The "Policies and Criteria" of the State Mining and Geology Board recommends a setback of 50 feet for ordinary risk structures, unless detailed studies indicate that a lesser setback is feasible.

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2. Groundshaking

According to a map issued by the Association of Bay Area Governments (Perkins, 1983), it can be anticipated that structures built along the Hayward fault corridor would undergo "violent" groundshaking (San Francisco Intensity B) in the event of a high magnitude earthquake on the Hayward fault. High magnitude earthquakes originating elsewhere in the San Francisco Bay Region would also be capable of pro­ducing earthquake damage in the Oakland Hills area, although it would be less severe.

At San Francisco Intensity B, even well-designed structures meeting the current requirements of the Uniform Building Code are likely to experience damage. The damage cost factorl for a one- or two-story woodframe structure is 12% (Perkins, 1982). Thus, if the proposed two residences have a replacement cost of $200,000 each; they could be expected to sustain on the order of $24,000 (each) in damage from groundshaking. This dollar estimate assumes that the build­ing envelope is not subject to surface fault rupture or other types of ground failure.

RECOMMENDATIONS

1. Surface Fault Rupture

Figure 9 presents our evaluation of faulting on-site and identifies a restricted building zone. Note that in defining the eastern boundary of the fault zone, we choose to be con­servative on the side of safety. Any features that showed possible evidence of faulting were included in the fault zone.

The setback from this fault trace recommended herein is 25 feet. The justification for the setback is as follows:

a) The proposed use is two single-family residences

b) Both building sites are shadowed by an exploratory trench. T-3 bisects the building site on one lot and is approximatley 40 feet from the building site on the other. Therefore, long projections are not involved.

l The ''damage cost factor" is equal to the cost of repair divided by the replacement cost. This quotient is multi­plied by 100 to express the result as a percentage,

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c) T-3 penetrated unfaulted colluvi.um. According to the USGS (Helley, Lajoie, et al, 1979) Quaternary deposits in this part of Oakland are considered to be of Late Pleistocene age (more than 10,000 years old). Therefore, trench T-3 indicates the area deemed suitable for development is not crossed by an active trace.

Structures for human occupancy should be avoided in the re­stricted building zone. The State defines a structure for human occupancy as one which has an occupancy factor of at least 2,000 person-hours per year. It would be possible to construct garages in the restricted building zone. However, they must be detached and the owners must recognize that any improvements in the restricted building zone are subject to a high risk of damage. In the event of surface fault rup­ture, structures astride the active trace(s) would be subject to total destruction.

2. Groundshaking

The design and construction of the proposed development should consider the probable high lateral forces induced by "violent" groundshaking at the site. The design should be conservative on the side of safety, and should be performed by qualified design professionals.

3. Trench Backfill

The exploratory trenches were loosely backfilled at the con­clusion of the field exploration phase of our investigation. The condition of this backfilled material should be consider­ed by the builder and his geotechnical engineer when the site is prepared for development. In our opinion, each trench should be properly backfilled during site preparation work.

STATEMENT OF LIMITATIONS

The scope of our services included a review of relevant published materials, a review of previous consultants• work in the area, examination of aerial photographs, a surficial site reconnais­sance, subsurface exploration, geologic analysis of the collected data and preparation of this report.

The conclusions and recommendations contained herein are profes­sional opinions derived in accordance with current standards of professional practice, and no warranty is expressed or implied.

This report has been prepared for the exclusive use of Mr. Glenn Craft, and his consulta.nts, and for specific application to the proposed project. In the event that any changes are made in the

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nature of the project, the conclusions and recommendations con­tained in this report shall not be considered valid unless the changes are reviewed by Darwin Myers Associates, and the conclu­sions of this report modified or verified in writing.

DARWIN MYERS ASSOCIATES

'b:u.,~~ Darwin Myers, CEG 946 Principal

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BIBLIOGRAPHY

California Division of Mines and Geology, 1982,"Fault Evaluation Report, Oakland East Quadrangle", unpublished.

California Division of Mines and Geology, 1982, "Special study Zone Map, Oakland East Quadrangle",

Case, J.E., 1963, Geology of a Portion of Berkeley and San Leandro Hills, California: Ph.D. Thesis, University of California, Berkeley.

Garbe, c.w., 1987, "Geologic Fault Hazard Investigation, Two­Parcel Lot, SW Corner Tally Place and Outlook Ave., Oakland, CA. 11 , (CDMG File# 2054).

Helley, E.J. and K. R. LaJoie, 1979, "Flatland deposits of the San Francisco Bay Region, California --their geology and engineer­ing properties, and their importance to comprehensive planning", USGS Professional Paper 943.

Herd, D., 1978, "Map of Quaternary Faulting Along the Northern Hayward Fault Zone", U.S. Geological Survey, Open File Report 78-308.

Nason, R. D., 1971, "Investigation of Fault CreepSlippage in Northern and Central California", California Ph.D. Thesis, University of California, San Diego.

city of Oakland, 1979, ''Special. Studies Zone Atlas", Published by Engineering Services Division.

Perkins, J.B., 1983, "Maximum Ground Shaking Intensity Map", Association of Bay Area Governments (scale 1:250,000).

Perkins, J.B., 1982, "Using Earthquake Intensity and Related Damage to Estimate Earthquake Intensity and Cumulative Damage Potential from Earthquake Groundshaking", Association of Bay Area Governments, Working Paper #17.

Radbruch, D.H., 1969, A.erial and Engineering Geology of the Oakland East Quadrange, California. U.S. Geological Survey, Geologic Quadrange Map GC-769.

Radbruch, D.H., and Lennert, B.J., 1966a, Damage to Culvert under Memorial Stadium, University of California, Berkeley, 1n Tectonic Creep in the Hayward Fault zone: U.S. Geological Survey, circular 525, pp. 3-6.

Radbruch-Hall, D.H., 1974, "Map showing recently active breaks along the Hayward fault zone and the southern part of the Cala­veras fault zone, U.S. Geological survey, Miscellaneous Investi­gations Map l-813.

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Scheirner, J.F. 1 and Mills, J.M., 1984, "Seisrnicity Rates for Eastbay Faults", Lawrence Livermore National Laboratory UCRL-53542.

Soares & Associates, Inc., 1987, "Fault Hazard Investigation, 8430 Ney Ave., City of Oakland, and Soares & Associates, Inc., 1987, "Addendum to Fault Hazard Inves­tigation, 8430 Ney Ave., Oakland CA (CDMG File# 2050).

Stejar, F.A. 1 1981, "Geologic Investigation of Proposed Single­Farnily Residence, Buena Ventura Street, Oakland CA. (CDMG File #2143).

TYPE DATE

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HAYWARD FAULT PLANE

Qc

CO~LUVIUM. Sandy ~layf stiff; Late Pleisto­ce-nc i!lge. (mapped "1ere inferred d~pth to bedrock is ~ 6 ft.) •

fg fran1;:iscan G1;1bbro

;: Line of S!:!i::tion

Qc

--?---?---?---?·--?---?--•? Fg Fg

fGJ" 6 Darwin Myers Associates

DAlE 5-23-89 JOEi NUMll~.R lOOl.BY

--------·----------

View of the cut slope on site, with fences on pi:operty incs. Bldg in left background is Baptist Church.

Note light­colored rock expos­e( in right foreground. It is weath­ered gabbro.

E:mosure of topsoil off­set and assoc iated sheai: zone in T-2 (Stat.0+36)

The orien­tation of zone is N341\

Topsoil off­set is evi­dance of active faulting.

PHOTOGRAPHS OF CUT 51.0PE(TOPJ

AND FAULTlBOTTOMJ

! l(,~J~I

7 1-- """

~l ,\ ~ ' 5~22-89

---.. ------~

Darvvin Myers Associates " -

,"Ofi.'l:.1.1<i<'- 2U(J2.89

I I I 0

I I

5

I 10

I I 0

I I

5

I 10

I I I I 0

I I 5

I 10

I

T-1 58 50

cs , 4.25 TSF

CS > 5 TSF

Gr ave I lens with 60 apparent dip

40

--2a

CS >5 TSF

CS>S TSF

2a

... ( ....... -N 48 E -·

30

---

East boundary l of fault zo~0

- _ la : - . --r

2a

2b

-........

Wedge of clavey sand moderate yelf w ish-brbwn

(10YR 5/4) 10 Steep

-0 is continuous artings - -

\ \

I I \,. -

I -~-- 1A ~ ~ --. "" __ ........ \ 2a I / I ..__ // l ~ .......... \ 2b I I

cs 0 4.25 TSF

dg

Canpressive strength (measured ln field ~ith pock~t pe'letrom· eter; uoits are tons/sq. ft.)

Ge-ologic contact (dashed wheFe gradi tlorutl)

0-e-c:cnpo-sed '8.atbro {textu;e of c-oarse·grained sand)

S'"1ea-rs

Roots

boundary of fault zone

Col luvium grades less pebbly and has more motst ure Conglomerate

cobble, pale olive {10YR 612) large, completely disintegra\ed, T-2

CS " 3.25 TSF

Topsoil mixed with dg

Shear zone: silty clay, dusky yellow ( 5 YR 6/ 4 J: N34W, 70SW

T-3

40 CS • 2.25 TSF

1a - -1b ----

CS ~ 2.0 TSF

Shear I cobble of gr ave I ·

( N 64 E-m.

NJOW, 65NE

#"Surrow? Topsoil mottled with dg

Parting: E-W, 52S N60W, 37SW

( N 45 E-.- Q

10 20

--b - - 1 -------1a

:iE.---- 2a --2a 2a

CS >5 TSF

1 a TOPS{)[ L. Sandy c:l ay, moderate brown (SYR3/4}, moist, siight plasticity, firm, massi.....e, many roots.

1b

2a

s1..=ss-:H L. Sit ty clay, m::iderate yel loioi'i-sh brown ( 10'r'i:i:5/4), mf.ist, stiff. cs~4.5 tsf

c6L LlY/ l ux. Sandy~ roe ky, p:ior l y · s or teC clay; rooder ate btown (5YR4/4); moist at upper cOC".ita~t to stightly moist '\ 5 ft.; slight plasticity, stlff; many tine 1oots. Peb­b es der i ved f rorn Franciscan A sserrb~ age ( chier-t , serpent i r..e, -gtoywac:ke, basal tz gabbrc) to 3" in rrax. dimension; t:oul · ~rs of i.ie-a thered g rave-l ( cong l ome rate) ~

2b -COLU...-"/H.IM. Similar to 2.a but less w-eathiered, rrrxierate yellowish brown (1DYR5/4}, slightly rociist to darip; fei..i roots.

3 GABBRO. Seve~ely -weathered, satt-and-per:per coloring, moist to darrp, permeable; 9~anr..,o;ler (sardy} textu~e with ifolated clasts of hard gabb~o.

3 a ~t1s.k y ye l l '°'" ( 5Y 6/ .G ~ 100% decorrpos ed g a.bbr o.

3:b Dusky ye-l lO!io! -gabbro; BO% decrop:iosed g.al:bro; 20% res~Wat ut ore11 9.al::bro.

3c P:ile- greenish ye-llow (1QY8/2) 95% decooposed gabbrc~

3d D;er:k yet lowl sti orange (1{1Y6/6); 95% de<:ooposed gat:bro.

The locations. aN,j Lirnite· tions of the geologic features shown on this map are accu:ate N:'presenta­tions of said fe3tures as they exist on th= grO\Zl:d;

LOGS OF EX PL ORA TORY TRENCHES

seJi,.LE 1 _.. : 5'

8 we:-e placed oo t;~l s rr.ap by DATE 5-23-8 g rne, or under my ~i.Jf><!rvis· ~---=-=--"------'-----------t io~~ and are ac6.Jrate to the- best of my l 1·"h.'""Wledge. Darwin Myers Associates Signed: }o.;,,,._.., fi._,.,,_.__, ~-----------------!

Dar.i'in Myer~ CEG 946 th..rt::ier:

JOEi kUM!IUt: 2002,89

I I I I I I I I I I I I I I I I I I I

The loc:ations and limitations. of the geologic fe-~tures shown on this fl'l.:'.IP arc accur-atc representcitions of s,ciid f~~tures as they exist on the ground; were pla~e on this map by rne 1 or under my supervislon, &rd ~r~ ~ccurate to the best of my knowledge.

Si

Nurrb~r~ CEG 94~

/ RESTRICTED BUILDING ZONE

~CURB o~-

i ..

T-3

B-3 • I()( J( J( J(

-----

7 __ ?° RL;

Troncn lo99ed by OMA (2 MAY 1969)

Borenole l09ged by A'<J. (6 Sept. 1988)

Active feult trace

E~st bourdary of fault zon~

Setback line

Area su\tabl~ for construction

~ FAULT EVALUATION MAP ~ ... 1--------------.--~----I "" ~C-'l! 1 • ,::: 2 51

FIGURE·

9 DATl: 5-23-89

Darwin Myers Associates JOB NLJM.9[11:; 2002.89