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James 0. BerKland County of Santa Clara Environmental Management Agency

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Land [\.ove1oDment En9lneerin9 arid Survevir1:~

C::JL1nt·, ·~~vernnetit Ccnr~r-, East' \-/ins 70 We•t Heading Street San Jose, California 95110

Dear Jim;

This is to ackno·,;ledge rece.iot of the 11 reoort,. cc·sign<iteC: '1n vour it:~ter of May 4j 1977, Eig!:t cf -::--::-:~.e rcDor-ts (fa'"" C2-·-: Pet"rota. \.-.:eeksf C~o~e~ Levln, Sci~, Kend2 1 ~, ~:;r-,d ~;,i~Jcr;::1 a:--~.~ i7 c~ sites ~-:it~~i~1 the Soecia'J Studie.s Zones an·: hnve been aporoved bv Santa Cl~r~ CoLl~ty in com~liance ~lth tho ~lquist-Driolo So~~~~: Studies Zo 11es Ac.t. They \\ri 11 be placed or: open fl ~E'. a~ rcc!J'. !'"C·.-·'

The t1·:01 report" (Trovao, Bumoarner) for sites outs id" cf th" zones wi li be Placed in our informal consu't1ng file.

For you: informatior1, have m.f'.)de ;J qLi::::,: check (1 f cur filf:S and determined thal 69 percent nf the repcrts rcceiv~d from Santa Clara County during the 1975-76 period indic<it<· the Uo;C

of seisriic refraction in f~urlt investi9ations. Compar~tivc.: d?.t;:; for northern and southern Cvlifornia for the sarne period o,-c C'!Vf'1 in the enclosed summary. I do not hove sto:f~.tic:s fo: 1 ?7(~"'Tl't bt!t 7 of rhr~ 8 r·enort~:; _iu:,t filed b~, yo._: f":- sites t·.rirhin Spr·.:::i, .. : Studies Zones also indicate use of seisl""".iC: refr.:iction. I cannot help but wonder ahout the popul~rity nf thl• method. Mosr geoloqist~ and geophysicists with whom I have discuss~'.d this rn;;ittC'r con.:.::-ide;- seisrdc rt·:rr,·:jction to be fnt:'.")j"'lclusive. tit tlcst vJith res:;.:.ird to ~::i:valuating the h~z~rd nf faul.~ ru~ture. ti.t worst it i~; ~islf'~.:.iding and ni~y nc~t. iclcritifv ex!s~·:r·,~: faults.

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cc: T. E. Gay Jr. '\.H. Chapman l\-P fl let,..,.,...~

Slncc.rety your:::,,

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EARL W. HART

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~:~!·c i·•~·-:-.o::!·.' ic ~!~ate h·1 genphysic~l

Office of the Stcte Gcolo;~s~ C~E.G. 93~:

t=.nvlrDnmen)•.·; f"."'nr.?~l"~erit Ag(·ni:::y Lend Devl:!''orme!l'~ En~1'."l~~t'lt'!1:1 t<'!lrJ .Sl1lll'l7:~'.1l'":r:

County of Santa Clara

C<·i1.r~1\·1 Govcrnn~~:n\ (::··, .. ,'.'.·\ t-·~::.,:1 v.:~~:,.:

7(1 WP.:-.~ H~·')dr>11 0t~P.~)\ San JoSf!, Cri.l1lnrn1a 9~:;110 299-287~ Area Code 41)8

California

Report No. -.,--. -·

2.

3. " ,,

4. ·.'L

,. ~.

6. "':* '

7.

e. *

9. #

10.

State Geologist C/0 Earl Hart California Division of Mines

& Geology Ferry Building

May 4, 1977

San Francisco, California 94111

Dear Sir:

Attached are ten copies of geological r•~orts submitted to James Berkland, Santa Clara County Geologist, under the provisions of the Alquist-Priolo Act. The reports are as listed below:

P.erort Street Owner Fi 1 e No. Geoloqist Date

Aborn !load Perry Carr 18576.ll J.C. Prendergast l /7 / 77 (CEG 955) Addendum

Aborn Road Frank Perrota l8S76. 5 ,. J. c. Prenderqast 1/10/77 (C:O:G 955) Addendum

Aborn Road S.G. Weeks 77Bl8.3648 R. Burton Rose 4/7 /77 (CEG 760)

Call of the Wild Chope 76Rl2.602 R. Burton Rose 12/8/76 (CEG 760)

Chula Vista Dr. Pichard Levin 17574.9 J.C. Prenderqast 9/H/76 (CEG 955)

Clayton r.oacl r~anuel Trovao 77r117. l :19~ Ed1-1a rd Danehy l/l~/77

76Rl7.602 (C<:G 8)

Cochran/r-1a in Weis 21575. l PT Surton Rose l 0/23/?E 75G21.208 (CEG 760)

Hawkins Lane !lumgarner 21574.20 .Joseph Gabriel 9/tl/75 (CEG 256)

Hebard Road Bruce Kenda 11 74Ml2.864 R. Burton Rose 2/14/77 (CEG 760) Addendum

Higuera Road Stan finberg 18S7S.2 1 r (_J. - • Prendcr0ast 11/16/76 (CE:S 95S)

An Equal Opportunity Employer

Approval Date , ..... -~·---·-

3/~/77 Rec'd :l/ l /77

3/ ~I 77 Rec'C: J/l/77

4/25/77

l /2!:/77

ll/l~/76

1/l!J/77

2/25/77

4/~0/77

3/4/77 Rec'd v~1n

ll/2~·'1C·

Mr. Earl Hart Page 2 May 4, l 977

* These reports concern areas not in Alquist-Priolo Zones but are included for your files.

# These reports are for single building sites which are exempted from the Alquist-Priolo Act.

JOB:plk Enclosures

Very truly yours, ~ c/-, ,,. ~ ' :; '"' . . ,::,,.;;i. '\fl.t.,i+.X_

James 0. Berkland Sr. Engineering Geologist

.. ,;:

•

R. Bu.Ion Ro .. , M.A. GEOLQGllSiT

E:N~INE:~f:tlNG GEOLOG,_9T

ie ... u .. oP'!NIA RE:Gl~TRATl.N)

ALUtD GEOPHYSICS

P.O. eox $S3 SAN ,.IOSE, GA. 91!-106

STATE GE"oWGrsT

Copy (!_o ('_H RA I\/ I ()1 A I N

ZI 3 ?<;;,I 7S & z.1.20~

A-P4.31

re(e i~tJ 111\~1.. Mts ~J::is ll-3.·-fi:., ?08

ENGINEERING GEOLOGY "\ .. ,. County of Santa Cl~ra .....__ _ _ _ Land Development Engineering --- . _ County Government Center, East Wing 70 Wc;st Hedding Street ')en J0'"- CA 95110

Weis Minor Land Division

APN 727-02-009 59.82 ac.

East of NE end Main Street

Morgan Hill, California

T. 9 S. , R. J E. , MDBM

In-depth Geologic/Seismic Report

File 75G21.208

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R. B .. ..i.,,, R,,,., !VI.A.

E'.NC~IN~"f.~•NG G~Ol..0(;1~T

IGALll""O ... N!,._. Rr".Gl!ITrlATION)

ALLll'D Gl:OPHYSICS

P.O_ nox 503

SAN ..:.t051t, C:.a.. 9':•'0G

Mr. and. Mrs. We is 2210 East Main Street Morgan Hill, CA 95037

Dear Mr. and Mrs. Weis:

October 23, 1976

Re: Minor Land Division APN 727-02-009 59.82 acres East of Main Street Morgan Hill, CA

In-depth Geologic and Seismic Feasibility Study

Thank you for the opportunity of stud.ying your south west sloping land parcel for potential division to 4 parcels.

This study conclusion is favorable from the geologic and seismic viewpoints, with certain outlined recommendations.

' Consideration was given to additional possible alternative sites along the upper ridge lir1e. Several potential sites appear favorable, subject to site specific examination.

The detail back pocket maps together with the photographs represent an exceptional perspective of your land show the basic suitability of your proposed land division.

If you have any further questions, please call at your convenience.

ex-:;; # '-&=tl:_r'(U.!J ~ . .,,() UokC:-

ame s B. Baker Graduate Geologist

6 copies

Respeetfully yours,

R. Burton !lose C.E.G. 760 G.P. J97

• 'rABLE OF CONTEN'rs

Letter of Transmittal

He port

Bibliography

Appendix Data

Illustrations:

• Preface Plates and Aerial

Photographs

Seismic Refraction Lines and Index

(In pocket)

Geologic Plate

Geologic Gross Sections

Relative Geologic Stability Map

•

Alqu1st-P:riolo Special Studies

Zoning Act 1974

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Telephoto view looking east from Interstate 101

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k 11 .... 1 ... , p.,.,, ~ t.i\. GE.OLOCIST

ENt";lr-.IEEnlNQ GEOL0

0GIST

IGALt•o11r~IA l=/~"(';IATl~ATION)

ALL I Lil Gt:OPI IVSICS

P,!'.). Box 583

SA~ .JO~~;. CA. 9~106 (40Bl 256-2609

Weis Minor Land Division APN 727-02-009 59.82 acres East of NE end of Main Street. Morgan Hill, California

In-depth Geologic/Seismic Study

~: October 24, 1976

Introduction: This feasibility study and report addresses

the 1974 Alquist-Priolo Special Studies 2oning Act criteria

and supplementary requirements of Santa Clara County. The

acreage is evaluated for a specific building site on each

of the proposed parcels, with general consideration of

additional sites along the eastern ridgeline. Wood framed

home construct i.on is considered as basic. Both geologic

and seismic factors and hazards are reviewed and correlated.

Four parcels are partitioned; with an existing dwelling on

one. Seismic refraction survey lines were run across the

approved building sites on the additional three parcels as

shown on the index map and the detail geologic plate. Plus

one week of field time was spent at the site with separate

flight time for aerial photographs. Office preparation and

aerial analysis time was not logged in report completion •

1o,,,1000 I

INDEX: Weis Land Parcel

APN 727-02-009 59.82 ac.

NE end Main Avenue Morgan Hill CA

T,9 S., R.J E., MDBM Contour interval "' 40 ft~

Mt, Sizer U.S.G.S. 7t' Morgan Hill 11 "

quadrangle II

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727-02-009 2 •

Location; This sloping recorded land parcel extends from

the valley floor to over the ridge separating Santa Clara

valley and the Anderson Reservo1r on the eastern side of

the valley. The south west corner of the parcel is at the

north east end of Main Street, Morgan Hill, in Township 9

South., Range 3 East, MDBM. The. composite vicinity preface

plate shows the area parcel relationship, the orthophoto

and elevation contour map present the slope aspects of the

property, and the detailed 1• "' 100 1 pocket maps summarize

the specific field study results, l.n spatial relationship.

Data: The basic geologic, geopl1ysical, structural, seismic,

fault, topographic and slope essential information must be

dispersed. onto a series of revelaut maps presented in this

report. Tl'\e conclusions and mitigating or limiting list of

recommendations are a specific portion or content of the

minor land division approval. A reverse recorded seismic

refract ion survey line was run across the most suita.ble and

practical building site on each of the three proposed_ parcel

separations f1'om the existing home unit. A Bison signal

enhancement se.i.smograpl1 was used in the field. Stereo aerial

photos were analysed for structural and fault lineations.

Ground and a.i.r photos arc incli:_d,od to emph~size pertinent

geologic and structural features •

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Contour interval ~ 40 ft .

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727-02-009 ) •

Geologic Structure:

Two main structure types are present:

Faults-: Three distinctive faults have been mapped

through the property; all trending subparallel in a NNW to

SSE direction.

The Coyote Creek fault cuts through the property at

the highest elevation and is marked by linear outcrops of

silica carbonate at the serpentine - Santa Clara contact.

Another fault marks the juxtaposition of Franciscan

greenstone with the Santa Clara gravels. This contact was

crossed by one of the seismic refraction survey lines and

interpretive profile (A-B) and is clearly disce:rnable •

The third fault appears to mark the alluvial contact

with the Franciscan melange and may be marked by the break

in slope where not concealed by landslide debris.

All three of these faults are considered probably active

by reason of their juxtaposing recently deposited materials

and_ the older rock uni.ts.

Regional active faults include the San Andreas, the

Hayward, and the Calaveras; all shown on an appendix map.

Foldin~: The Plio-Pleistocene Santa Clara gravels

were mapped by Dibblee (197)) as being in a gentle synclinal

t'old striking NNW - SSE. This geometry is depicted on the

cross sect.ions in the back pocket, but were not verified in

this study_ since attitudes were not e:x:posed within the Weis

property limlts.

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727-02-009 4 •

Geologic Rook Types:

Several distinctive rook types (units), as well as

s1gnifice.nt surf1cial materials, were identified on the

Weis property,

Field mapping, air-photo interpretation, and seismic

refraction survey profiling were used to delineate their

geographic extent (see geologic map, back pocket). The

following sections describe these units in detail. One

type group requires additional perspective:

Franciscan melange (KJfm) Cretaceous age

The term "melange" is now commonly used to designate

masses of rocks cf diverse origins which chaotic mixing

has arranged in a sheared matrix (Hsi.i, 19'/1 ), Current

hypotheses suggest that sometime during l,ate Triassic

time (Tithonian) a submarine trench .opened near the western

coast of the North American continent as the Paciflc plate

was subduoted beneath it. Terriginous, biogenio, and volcanic

layers intermittently accumulated in this linear trough

(eugeosyncline){Blake and Jones, 1974). As these materials

were forced down beneath the continent, extr•eme stress

sheared and mixed them while producing low grade metamorphism.

Innumerable dislocation surfaces have disrupted the

stratal continuity to such degrees that mapping of' different

rock units in the m~lange yields little systematic under­

standing of their distribution.

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727-02-009 5 •

GEOLOGY - Rock Units:

This following summary of rock types exposed in the

Weis land parcel is a composite of site field observations

and literature reference descriptions.

Cretaceous age metamorphic isolated "knocker• (Tectonic block)

This isolated boulder ("knocker•) of mica schi3t,

approximately 20 feet across, is located behind the residence

at the south west corner of the property, just above the

valley floor. It has a striated chlorite-actinolite

·peripheral shell. Where cracked in half, the metamorphosed

interior shows veinlets of lawsonite (?). The shell coating

of chlorite minerals is slickensided and striated parallel

with the rounded surface of the block.

This "knocker" 1.s a classic indication Of the melange

nature of the Franciscan unit as exposed here. A mass of

elastic rock, carried to a great depth (10-20 km) by plate

subduction, must have been altered to schist and then worked

its way back up the sabduction zone to the shallower depths

where it eventually became mixed witl'i. the graywackes and

cherts which also outcrop here (Hsu, 19'71). Its presence also

suggests. that a fault intersects the surface near this break

in slope •

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Single ellip3oidal knocker of schist

(cracked in half) located .i.mmediatt0•ly

behind the a xi_ sting rcsi<honc e

(photo courto<;y of Tony Nisich)

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727-02-009 6 •

Franciscan graywacke with shale (KJfmss>

Exposures of these cJ_ast ic rocks are dark, foliated,

and discontinuous. Isolated outcrops, separated by wid,e

expanses of nondescript light-colored sandy soil, exhibit

poorly defined and irregular bedding which is usually too

foliated to yield reliable attitudes. Mild metamorphism

has produced flakes of mica which create a distinctive

glisten when reflecting sunlight. Overall, st1•ucture is

discontinuous and chaotic. Veins of quartz and calcite lace

most exposures and indicate the great extent of tectonic

disruption these materials have undergone. The rock is

hard and dense, yet so foliated and shattered that outcrops

are usually surrounded by talus accumulations of platey

fragments,

Franciscan chert (KJfmch)

Isolated blocks of chert outcrop in a broad band

along the first ridge line. Bedding is apparent in most of

the masses which are fine grained (probably Badiolaria) and

veined with quartz (see photo). A notable exception is a

large outcrop of rhythmically banded chert in which

brilliant blue and white bands of chert are shattered and

dislocated with fine veins of lighter colored quartz that

runs transverse to bedding planes; Conspicuous cavities

extend along the bedding planes indicating the altei•at ions

and recrystalization which these rocks have undergone •

Foliate<i and minorly recrystalized graywacke anci_ mudstone with fist-siz.e cobbles of basic igneous rock are typical in isolated outcrops in the area of Fran6iscan m~lange.

Blocks of reddish radiolarian chert with veinlets of quartz are exposed in several isolated outcrops and are indicative of the intimate mixing of the different rock types which has occured in the melange.

•

727-02-009 7.

Franciscan greenstone (KJfmg)

Actual outcrops of these altered extrusive basalts

are non-existant on the property. Rather, the surface is

littered with small pebbles (i"-1") of aphan1t1c greenstone

with characteristic vesicles and dark pseudomorphs after

olivine. Some cobbles of tuffaceous greenstone are also

present.

These rocks were probably deposited as extrusive

flows on the sea floor and subsequently subd.ucted to depths

where mi.nerals were altered and original structures sheared.

A band of this rock ls in apparent fault contact with the

Pllo-Pleistocene Santa Clara gravels about half way up the

property slope •

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727-02-009 a.

Cretaceous and Later serpentinite •serpentine• (sp)

This ultramafic rock is in apparent fault contact

with the Plio-Pleistocene Santa Clara gravels (Coyote Creek

fault). The mass, which extends eastward at least as far

as Anderson Lake, is most likely in intrusive relation to

the basement rocks.

Slopes underlain by these rocks are characteristically

boulder-strewn and. covered wlth distinctively different and

less dense vegetation {see photo) owing to the peculiar

chemistry of weather products. Oxidation of abundant iron

minerals gives a distinctive reddish-green .hue to the soil.

Digger pines and manzanita thrive with these conditions.

A five foot cut into "fresh" rock at a building site 20

feet beyond the north eastern property line in Holiday Lake

Estates revealed the 1 blocks in a sheared matrix' character

of the serpentine mass. The blue-green blocks consist of

completely serpentinized peridotite or dunite with the

original textures preserved. Olivine and pyroxene crystals

have been replaced by serpentine minerals (ant1gor1te,

crysot1lc and bowl1nglte) and outcrops are typically bumpy

owing to differential weathering of these pseudomorphs.

Blocks are rectangular to rounded and set in a sheared

matrix of soap-like pulverized rock with many foliations

and slickensldes •

i !

Look i.ng north along the strike of the Coyote Creek fault. (Note the topographic expression and BOK pond at left.) Blocky outcrops in foreground are typic~l serpentine areas •

.... ,

Outcrop of silica carbonate rock follovJs the trend of the fault, undulatinr, foliation dips steeply ( 75°) to east.

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727-02-009 9 •

Cretaceous to Pliocene silica-carbonate rock (scr)

Along the fault contact between the serpentine and

the Santa Clara gravels is a relatively thin (1-3 feet)

layer of dense lenticular rock that crops out along the

strike of the contact as rock-wall type exposures. The mix

of silica minerals (chalcedony, opal and quartz) associated

with carbonate (chiefly ferroanmagnesite) ls apparently the

result of hydrothermal alteration of serpentine along the

fault plane. Shiney black crystals of chromite remain from

the original serpentine nature of the rock.

Because of the resistance to erosion, these relatively

thin lenses stick out of the ground in a very characteristic

fashion (see photo), as well as forming the "backbone• of

the r-idge. Weathering of the. carbonates has reduced the

rock to a porous network of silica veinlets stained with

residual iron oxides (Bailey, 1964, p. 87) which produces

a typical "thunk" when struck with a hammer.

The sheared and undulating structure of the rock

suggests that it ls the alteration product of equally

sheared and foliated serpentine masses and further confirms

the fault related nature of the material. The hydrothermal

solutions which originally produced the rock commonly carry

metals (like mercury) into the rock; however, no cinnabar

was found on the Weis property •

c•

727-02-009 10.

Plio-Pleistocene Santa Clara gravels {Qtso)

As used herein, the term applies to a poorly

consolidated unit of coarse, angular gravels, sand and

clay, which is poorly exposed and underlies more than

half of the subject property. The charaoteristio reddish­

brown soil that it produces, and the small rounded chips

of lithic fragments which are brought up by burrowing

animals, clearly indicate the extent of the rook material.

However, no good indication of the total thickness of the

unit as exposed here could be found. The syt-iollnal nature

of a broad fold indicated in the cross sections is

primarily based upon that interpretation presented by

Dibblee (197)), Generally, however, the geometry of the

several slope failures suggest that this synclinal relation

is probably correct.

Quaternary to Recent alluvium (Qal)

The flat area at the south western end of the property

is the beginning of the broad valley. Unconsolidated sands,

gravels, and clays have been carried out of the hills

by streams and laid down as a broad continuous apron. 'rhe

fault mapped along the ridge front could be responsible

for the abrupt nature of the alluvial contact with the more

resistant Franciscan rocks.

This is the only clear exposure of ~anta Clara Formation on the parcel, owing to the ease with which it ero,les and developes a soil proL.le. 'J'he vravel appears to be predominately locally derived Freenstone from the Fr•anciscan. 1rhe clays make a very poor cement anci contribute to th8 unstable naturH of slopes underlain by th_i.s l.lnit.

~- .. ' . *'.. .. .. . . .. ..•..

•

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Stereo triplet vertical aerial allows for three dimensional view of parcel. Slope failures show by their char•acteristlc bowl-t>haped head scarps and bulbous toes. Also, two of the three faults are clearly shown by the abrupt discontinuities in soil tone.

0

"' °' II =

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727-02-009 11.

Quaternary to Recent landslides (Qls)

Several large rotational - flow type slope failures

are indicated on the accompanying geologic map and cross

sections. The forms of these landslides are somewhat

modified by erosion, obscuring their geometry and extent.

Analysis of stereo-paired aerial photographs of various

scales and dates provide the different lighting conditions

and soil moisture distributions·necessary for interpretive

delineation of these masses.

A complex of several generations of failure is

evident at the ridge front in the Franciscan. The other

slides, several of which have well preserved, bowl-shaped

head scarps, occur in the Santa Clara whe1•e deep inc 1.s ion

has undercut the stability of the slopes. A very large

landslide (Spencer slide) extends from the ridge line out

onto the valley floor. The mass of this slide is mostly

sheared serpentine which weathers out as blocks on the

surface. This distribution led to an erroneous designation

on the adjoining parcel as serpentine bedrock. Actually,

the blockaof serpentinite observed on the adjacent knoll

are coming from a cap of landslide debris resting on Santa

Clara gravels (see photos) as the cap erodes away.

Panoramic mosiac looking NE and East. Both property lines are marked by fences at left and right. Features in this area indicate relatively active rotational landslides with'exLensive erosional incision.

Closeup looking upslope to the northeast of the most active landslide.

Low sun angle view looking north at higher elevations of the slide area accentuates the hummocky surface and active head scarps.

Looking south at isolated knoll just beyond limits of the parcel. Note the horizontal discontinuity in soil color and feature. Blocks of sheared serpentine litter the surface.

Another view looking SI< shows trie knoll and an area of similar material in the foreground. Both appear• to be the remnants of landslide debris. 'rhe material on the knoll is now an isolated cap cut off from the main body of the Spencer landslide.

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727-02-009 12.

Recent expansive colluvium (exc)

Accumulations of slope wash and creep ( colluvium) soi[

with high clay content exhibit a strong tendency to

shrink and swell with the change of dry and wet season

cycles. Winter rains saturate the material and the water­

absorbing clay minerals increase in volume. The following

summer, this material drys, shrinks and cracks. Cyclic

cracking mechanics indicates that the cracks open towards

the down slope side and close from the upslope side. The

bulk behavior of these solls on slopes is to slowly move

the broken material down hill, termed •creep•. This cyclic

movement constitutes a significant hazard to development

and these areas have been mapped on the basis of extensive

cracking observed during the dry su111111er •

' .

Aerial view looking north. surf'ace in midct.le elevatior1s, slope failure.

Note hum~ocky indicative of

•

•

•

727-02-009 13 •

Seismic Refraction Survey:

Three reversed recorded seismic refraction survey

lines were run, one at each of the proposed building sites

on the undeveloped division parcels. A Bison, Model 1550,

signal enhancement seismograph was used. Time of the shock

wave travel was measured in milliseconds, between hammer

blow stations and the end point recorder. Velocities of

sub surface horizons were calculated in feet per second.

Depths were computed in feet below the surface at the line

end points, offset in the direction of measurement. These

depttsprovide the data for the geoseismic profile in context

with the geologic and other facets Of this report. Three

distinctive velocity ranges were recognized:

Vl 770-1)00 ft,/sec.

v2 2000-4000 • n

VJ 5600-12000 • ,,

Soll mantle

Weathered bedrock

Fresher bedrock

Depth

31-18 1

33'-38'

A setback of 20 feet is recommended from the possible fault

contact on line A--B at station 80 •

•

•

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C 1, INSTRUMENTS ~ 5708 - 36th Street West

St. Lou is Park, Minn. 55416 Tr-i~'"honP 61 ~ 1fJ?6-l"M6

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FIELD N 0 TES ...;:~.:e>e1:.:::._,..!:r;=;.e.:.!..:""~._~~A<;;..:H-':=_..::~::.::~:.'.A'<:::..::""'..::>£:_..::~...==·c..::2::.,.. ______________ _,=-=:-= "'!F-970

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TRAVERSE C-£)

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FIELD NO TES _::!2 /a:># SE CoR.Pc/. 4

13

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TRAVERSE

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F!ELO NOTES---~--·----------------------------"1't=-o..,.-n.

•

•

•

727-02-009 14 •

Relative Geologic Sta~liti:

A map of the relative geologio stability has been

generated as an overlay on the geologic map and is included

in the back pocket. The following table explains the

meaning of the stepped categories. The condition ls

described, the hazard outlined, and the potential for

residential development given. Three building sites were

spec1f ically investigated and approved. These areas are

labled with "A" and colored green.

'l'he several broad areas labeled "B" are also suited

for building, but require additional site specific study

to verify the general analysis of the stability of these

at~eas .

The other categories are increasingly more restrictive

in t<?rms of information needed and possible problems that

confront development.

The areas labeled "F" and coloreci red are deemed

unsuitable for residential structures due to the definite

indication of active hazards; such as active fault rupture

potential or la.nd surface failure.

It is noted that all of the parcel, surrounding area,

all of central and southern California are subject to

future severe earthquake snaking; a pervasive hazard that

requires engineering design attention •

• SYMBOL

A

E

c

D

E

F

Questionably stable

Least stable

• RELATIVE GEOLOGIC STABILITY CAJ'EGOB.IES

CONDITION

Site investigatiori specific, including seismic refraction line (see profiles}

Relatively flat areas apparently free poor geologic factors (no site specific data)

Excessively steep slopes: may become unstable when graded and/or loaded

Expansive soils are indicated by some contraction crac~ing in summer

Setback areas adjacent to inferred faults or accumulation expansive colluvium (extensive)

Identified potentially active area {faults & landslides a problem)

HAZARD

Minimal hazard_ *

Suggested minimal geologic hazards by general analysis *

Structures subject to distortion from differential slope failure action

Shrink-swell behavior of soil may affect foundations and structures

Likely major ground distortion or down­slope creeplid.versely affect foundations

.

Surface rupture due to faulting or slope failure could damage any type structure

.

• DEV ELO p ViEN'r POT Eci'T" IAL

Suitable for single family wood fra:ned structure with approved soils engineering

Probably suitable with normal geotechnical site specific study

Special engineered :ype foundation design may be required

Subsurface data on soil properties necessary for specific evaluation

In-depth study required for possible placement of any structures

Unsuitable risk associated with any development: open space category

* ~round shaking is a nervasive hazard in all areas a~d re~ion

• 727-02-009 15 •

Conclusions:

This proposed minor land division is approved on the

basis of the plot plan lines used in the index reduction for

the seismic refraction survey positions; with the following

requisite recommendations: from a geologic and seismic basis,

Recommendations:

One of the recommendation made in the field has been

incorporated into the road design; that or increasing the

culvert size for maximized runoff capacity under the major

fill section. Other mitigating requisites include:

1.) Wood framed house construction.

2.) Relative geologic stability chart and map be

• included in development planning.

•

J.) Minimum acceleration factor of 0.2 g be used in

design from a geologic and seismic viewpoint.

4.) Engineered foundations be used.

5.) Grading cuts be kept minimal to the extent possible.

6.) Runoff water be controlled around home sites and

6 copies

no ponding permitted adjacent to structures.

Respectfully submitted,

R. Burton Rose, M.A. C.E.G. 760 G.P. 397

<-? 'B,_"Lc--ames B. Baker

Graduate Geologist

•

•

•

BIBLIOGRAPHY

Bailey 1 Ed.gar 11. 1 William P, Irwin, and David L. Jones; "Franciscan and Related Rocks, and their Significance in the Geology of Western California"; Bulletin 183, California Division of Mines and Geology, 1964

Blake, M. c., Jr, and David L. Jones: "Origin of Franciscan Melanges in Northern California"r in Modern and Ancient Geosynclinal Sedimentation; R-:- H. Dott,Jr., and Robert H. Shaver, ed.; Soc. of Eco. Paleo. and Mineralogists, Special Publication No. 19, 1974

Berkland, J. 0., et. al.; "What is Franciscan?"; American Association of Petroleum Geologists Bulletin, vol. 56, no. 12, pp. 2295-23021 1972

California Division of Mines and Geology; Seismic Hazards in Santa Clara County; Special Report 107, 1974

Cooper, Clark & Associates; Preliminary Technical Report Geotechnical Investigation, City of San Jose's Sphere of Influence, April 24, 1974

Cotton, W. R. ; Preliminary Geologic Map of the Franciscan Rocks in the Central Part of the Diablo Range, Santa Clara and Alameda Counties, California; USGS and HUD, SFBRS, Basic Data Contribution 39, 1972

Cummings, ,T, C. ; "The Santa Clara Formation and Possible Post-Pliocene Slip on the San Andreas Fault in Central California"; in Proceedings of the Conference on Geologic Problems of the San Andreas Fault System, Stanford University Publications, Geological Sciences, vol. XI, pp. 191-207, 1-68

Dibblee, 'l'. W., JR.; "Preliminary Geologic Maps of the Mt. Sizer and Morgan Hill Quadrangles, Santa Clara County, California", USGS Open File Maps, 1973

Dickenson, William R.; "Table Mountain Serpentinite ~xtrusion in California Coast Ranges"; Geol. Soc. of Amer. Bulletin, vol. 77, no. 5 1 pp. 451-471, May, 1966

•

•

•

Dickenson, W. R., et al.; "Test of the New Global Tectonics; Discussion"; Amer, Assoc. of Petroleum Geologists Bulletin, vol. 56, no. 2, pp. 375-384, 1972

Helley, E. J., and E. E. Brabb; "Geologic Map of Late Cenozoic Deposits, Santa Clara County, California"; USGS and HUD, SFBRS, Basic Data Contribution 27, 1971

Hst\, K. Jinghwa; "Fransican Melanges as a Model for Eugeosynclinal Sedimentation and Underthrusting Tectonics"; in Jour. of Geophy. Research, vol. 76, no. 5, pp. ll62-IT70, Feb. 1971

lrwin, William P,; "Franciscan Groups in the Coast Ranges and its Equivalents in Sacramento Valley, California"; in Bull. of Amer. Assoc. Of Petrol. Gaol., vol. 41, no. 10, Oct. 1957

Leighton, F. B.; "Landslides and Hillside Development"; in R. Lung and R. Proctor, ed., Engineering Geology of Southern California; Association of Engineering Geologists, Los Angeles Sect~on, Special Publication, pp. 149-200, 1966

Mooney, Haral M.; Handbook of Engineering Seismology: (in progress edition) , Bison Instruments, Inc., 1973

Page,B.M.; "Time of Completion of Underthrusting of Franciscan Beneath Great Valley Rocks West of Salinian Block, California"; in Geol. Soc. of Amer, Bulletin, vol. 81, pp. 2825-2834-,-September 1970

Rogers, T, H. ; Environmental Geologic Analysis of the Santa Cruz Mountains Study Area, Santa Clara County, California; California Division of Mines and Geology, Open File Report 72-21, 1972

Rogers, T. H., and C. F. Armstrong; Environmental Geologic Analysis of the Monte Bello Ridge Mountain Study Area, Santa Clara County, California; California Division of Mines and Geology, Preliminary Report 17, 1973

•

•

•

Rose, R. Burton; "Portable Seismic Refraction Studies of Shallow Geologic Structures''; in XXth International Geologic congress, Mexico, publI'Shed 1958

Scott, James; Anderson Reservoir Landslide Investigation; Santa Clara Valley Water District, January 1976

Aerial Photograhs:

low altitude, oblique, color photo courtesy of James o. Berkland (35 mm taken in June 1976)

vertical stereo triplet - enlargements of 24: frames 25,26,27, original black-and-white 9" X 9" s scale 1:12850, flown 5/27/65 (available courtesy of USGS Library)

vertical frame (ac.companied by diagram) -enlargement of 9-19A, original color 9" X 9" scale 1:21300, flown 6/26/74 (available courtesy of USGS Library)

vertical stereo-pair (not included in this report) -AV-546-01-03,04, glossy black-and-white Q" X 9" s scale 1:12000, lown 6/26/63 (acquired from Pacific Aerial Surveys)

Map Base:

proposed parcel boundaries and road alignment from Preliminary PARCEL MAP, MH Engineering

topographic contours generalized from USGS Mt. Sizer Quadrangle and modified with detail from field observations

•

•

•

Selsmlclty

Plates -- Data

•

•

•

•

PM:5TJK!-'.D LPin1"'t~:R ot•

IJ>ll..IL l8, 190~ r.ARI'HQU~

t\AG. 8. J

l'P.ESUMi:.:0 !:PICE.l'l'rtR OF...__,~'"l JUIB1lB38 °E.Po.Kl'l-IQL'll'l.KE

MA~ITUOE 7.0iQ.~

~M-t (. ; P+.IJ P'RCSUMEO EPlCl-".Ni'ER or OC'l"Q?..RR 11. 1869, •'.J!.RT\!QUAAl'. MAG~HTUOE 7 .. o:to. 3

. . .. . . PRESUMED t;PICENTER OP' / JULY 1 1 l9ll I:ARI'llQ'JAKE •:.

N l"f t $·. J.,_.,,..,,. , .. 1 •,' p 1-S. \: ~

o~o '~·~ ~Rli:SUMEO E"S>ICENTER or ~($.I) z QCZ'. 12 1 1926 EA~HQU•\KE : 0 o

ff'l-tl 1.,_1'1 n-.; o • p 1') \": ~ 0 ••

0 0

FAULT JOAQUIN

FAULT ' _,.. ~.....,

.. /' ,/

/STANISLAUS

·• 0 ., '

A ) CALAVERAS

I , '..J''-".., /,

' <

/ , /

............ /!' 0

' "" 0

,

' 0

, I

\

PALO COLORADO - SAN GR~GOR!O ,?'f \ BtNITO '., •-.,

' " 0 0

FAULT '

0

'"' "' • A

1•.21

E'.<P1,,.ANAT_ION

M.(<"Jni.tudu 4.0 - 4.? M./l.:Jilit•J"e S.,O ~ ~.9

t~,,9ni'l:.1.de 6.0 ~ 6.9 1'1<.!1JHitu,iiJ 7,0 - 7.9 r..1gnitu,J~ ~ 0.0 Maqnitu<.le of selecte~ Q~rthq~.ti.k~s

Fil]Ut't'.!S b~oi<l~ t.hc lo<:~t.tQn~• iridit::.).te th!! nu.'l'i)ez- i;.11'.: (>•1rt:h'.lli.:a:A~~ a.t U1(: '0-.iz:·.e pla.::l!I,. all ~quc!l. tC! oc smallll'!~ t.hil.ll t.he a'~ p).otl'..@d.

~ N.

~ 0 " 16 ~

'S(;Al..E !N MU.ES

o.

MON

0

..

o· 0 ' ' ef'' •SAN ANDREAS

FAUL.T .J 0

\',\ ~~ .. _j ....... 1

•'

0

Figure 12. Major faults ;ir1d earthquakes in the greater San Francisco Bay arc~ (modified after Rogers and Williams, 1974).

33

•

•

•

,_

, APPENDIX 8

General Comparison of Scales Used to Rate Earthquakes at the Earthquake Epicenter•

Jnt.4!!nsity

Ma'l!'l!t.ude Richter sea.14!1

Rali•i~FoU'l mivaler,t.

l l

u -1:.,,..Il

!I% JU

S.5 IV ·J lV-V

v Y.Vl

,,. Vl-VIJ:

s.s ,,.. Vll!

Vlt! Vlll-U

8.0

•••

Net. folt. •:icr;111111pt bJ' few \Q'lder f•v.)r•t.. c:it"et:m&t~

relt. noticeatily 1ndoOn

Pelt gene:r.ally i..n4oolW

:Palt by a.11, IMllJ' frtgh.t.aIW4

~~eyori• run.t CKA­d.oon, f•lt:: i..D. 'ill()Vin.9 ca.~

h"1o

V•r')" de.!!1tr13C'il ve ~ 9ene;r~l c!.1m101.9~ t.o ~•o!lk 5t.t'tlet&r9~. Little dam.aoge t.o well-built .ut~e-t.una

'l'Qt.al i!est.rui;;t!on. w•tJc 11t.ri.u~tunis, eon.sidct'~h

d;w.~e "'•ll.-bui lt. atnet:.urU

?-'laaon.ry .ut.d !r~ .tr..ructl.U"U ~ly

destroy~. Cinly be•t build.in~• •\ll'Viv•

o.lte&t;zlr •U1J~ d:l!J•et.a i>W!l\f

ni.t:hi!'Sr v;i.ti.~. b~ pttndu.l\Qll <:locks atql

f'uni..i. t. UXll 'lflO'ill!;d._. d;iject.a \lf'S•t

,•

~n~!!.t,'!I .. ..,&l.hi Q.oi.m., f~it\.lt'* (Wtl:t<"'

t.uni.•d· S.anil and. ~~ t!jl!l.;:t.i!;d.. Ol&nl]9:• i.n WiSll-Wit.t.111.t' 111Rl..t

ro\tt!.dati01'1.!11 d~ve4~ \i,t'o~r·-9J:'Ound p:f.p.a bxuk<i:D.

Ct'Qund P.:.~ly er~, rails bent. We:t.eE' •l.Qpi;ed gVt!C bi~

'D'l'Qad. fi.$~~· ~ t•ul.i. •earpar Ul'J.dar'"""9't'l)'lln4 pipes out. of so~c.

a~c~le~&t.ion -..ee~

9r.s.vi t;:y. W;ave• i1111;•t1.

i.l'!. 9;t0urtd.. LiM:f. Of s.1.ght And. level d.i9.~t,.~, d;lj•~ __ ....,.u

NOT![ ~it.ude .&r14 l.ntenstty of ~ ~arthqiJ;U:.e arw 1SJ1.ti:1:elY dl!fe~t .measuremi!.b.t.9 ot .tt~.aJc.1111 ·~ o: ~tl"eCU,.. ~d. can oo.ly b1111· ~4.rej .ae th• •~qu~• ~_piccmt.er-.

Maanit:\.ld~ - it! .it nl,l"'".,ber de:-ive-d .f~ in.'l·t~n~a1 pr.8::9.urewnt.$. a?ld is th• W.4!1A".ln ot the •MJ!WJ" t-~1.euod. ~ u;;-;arthqullllte. 1'r.~e i$ ~ 1'A.';lniti.:.d~ <=41.l~l.a.U:d !or e;:r.i;h eart.hqt.!Aka.

~nsl~..t - i• ;a l.~al :i:-a.tin9 of e.u-tl".qt.tdkil!! effe~ oQsi!!;i=ved. m:'.ld :report~d by PeopU. at ari.y 9ivmt l.oeati~. Int~r.i:!Jity .ri.tin9'• for Ul'!.1:.- e.-.tth.JUa:.~e vlll"f c~ider~ly depend.i.n.g QI) "-1.st.an1;:t11 tram •pie:e:nt.911', th• r • .iit.w."e of the io.ol.l. &r1~ t'Qek beneatl, th• l'.:bse~i:, a.~ ~e ~•~.t"Ver'11 !.i'lt.e.eynut.i~n ot. evv:r:i.U .!leen ot' .C.lt.

36

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Table 4.1. Ior:AL1zro RrLA11os ar.rY.'ElN MAcr-:1ruoE. A!'-i'D Ll:.SGTH OF SLIPi":ED FAULT

Table 4.5. ExPEcr.a.t10~ oF EARTHQUAKES JN

CALIFOR!'>ilA (150,000 lnP-)•

Magnitude

4.n-5.25 5.25-5.75 5.75-6.25 6.25-6.75 6.75-7.25 7.25-7.75 7.75-8.25 8.25-8.75

Number per 100 years

250 140 78 40 19 7.6 2.1 0.6

•A~wci~1~d with large ~arthquakt!~ are .;h.i'Stc~ i;ir sm;:illtr ~arthq1,1l1kes that l'll"'Y prbdu~ repcli[i\'C ~h~king cif the- sarnit lo.;:11tion- To disCOu;J.t 1hi'S fQr pn;ib­abililY 1;.11k11latio11s, some of Lhe eanb.Q\J.il1'C::lo ha\·ing .'IJ < 6.0 ha\C been Qomitled.

Table· 4.6. PERCENT P~OHAtHurr or A.CCE:LERATroN

AT A LOCATION IS CALifOR~IA

In period or years

.(\occ:leration 10 2S 50 JOO (%&)

~ s 65 92 99 99

~IO 37 70 88. 98

~ 15 19 41 64 87

~20 10 23 40 63 ..,, 25 s i2 22 37

~30 2.5 5.S 10 19 ..,, 35 1.0 2.5 4.4 8.7

of course, a po.sibility that the site is covered more than once by the >pccified ground acceleration and the prob­ability of being covered 11 times is

( ) (a)"I -•'"' p n,a = A n!e (4.2)

It should be noted that the probabilities given in Table 4.6 are too high for some of the less seismic regions of California and too low for some of the highly seismic

regions.

1ables 4.1, !!:..:..2• 4.6, l!J. Earthquake Engineering

•

•

•

BISON SICiNAL ENHANCEMENT SEISMOGRAPH MODEL 1550

Modal 1550 is a rugged. light·we1glH statc-uf-the-nrt signal enhanccrnent engineering seisn1ograph designed for rapid and effective subsurfaco cxplora,, .tiori. Its niost irnportant applications arc in determ1niri\:I depth to bedrock or other subsurface boundaries. rind for engi­neering classification of rnaterials at Uept·h. The field work is carried out corn­plctely at thr: surf acc. If used ris a supplo­mer1t to an explorrJtory drilling progran1. custs C<In be greatly reduced while ex­panding the inforrr1ation obtained.

The 1550 is a snpt1isticntcd multi­function instrurnent with many of the same fealurP.s as H10 larqer, more expen­sive Bison seismographs. !"his incliides tt1e C(Jpabi\ity tor 5ign(JI enhanccn1ent, iritrod1iced by 81::;on lnstrun,ents which permits its use alrnost anywhere - even in congr.sted tr(Jffic and construction areas,

Its curnpact size and light weight, to-9ether with its brillicint cjisplay and func .. tional controls. m.o.ko it useful to civil engineers. geulO~Jists, contr(Jctors. well drillers. (.Ind geophysicists engaged in:

Highway co11strucllon Damsite Investigations Bidding and estimating Groundwater studies Gravel and quarry prospecting Foundation sludies Geological and mining surveys

Explanation of signal enhancement

Signal enl1anccrnent is a powerful signf11 processing technique which ainplifies the true seisrnic signal (.Ind reducc5 t11e noise interference produced by wind, traffic. and machinery. It accomplishes this by electronically summing and stonng the scisrnic waveforms produced by two or more hamrner impacts at the snrr1e locat!on. Tho noise signals arrive at random tirnes so they tond to cancel in surr1rnntiun. The true scisrnic signals are perfectly repetitive in arrival tirne and waveforrn so they are amplified and enhanced by summation.

The effect of :)igrial enhancement is tu • Increase the depth of investigation by

a factor of three or more, compared tc) a seismograph without signal enhancer11ent.

• Permit oper.J.tiun under adven=,1° cond.itions of wind, machinery, u1 traffic.

• ln"'lprove ease and accuracy Oi reading.

• f·~educe field tirne by reducing U11~ nu1nbcr of irnpacts necessary to get< reliable reading.

W<ivdorm without 1.1nhancem9ril. True seiS1Yiic sigr1;_:tl.~ ;1f~ difficult to (listingul$h from nOi$f':!

C::Qmpo111te (11umrr10d) wawefor11'1 generated by tl'!ree 11ucce11~IV~ Impact •lg:nala. SeisIT1ic $ignals arc a.mplifieO and clear\1-(listinguishilblo,