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STATE OF CALIFORNIA.
ARNOLD SCHWARZENEGGER. GOVERNOR
RESOURCES AGENCY
D. E PAR T MEN T Of
CALIFORNIA
801 K STREET
PHONE 916/445-5488
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CON
GEOLOGICAL
MS 12-32
FAX 916/322-4765
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SACRAMENTO.
S E R V A T ION
SURVEY
CAUFORNIA 95814
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TDD 916/324-2555
WEB SITE conservation.co.gov/cgs
RECEIVED
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Mr. Howard Smith
District Structural Engineer
Division of the State Architect
Department of General Services
1102 Q Street, Suite 5100
. Sacramento, CA 95814
JUN 1 5 2006
,
MAINTENANCE
May 17,2006
Subject:
Review of Fault Displacement Estimate for
College of the Re,dwoods - Eureka Campus
7351 Tompkins Hill Road
Eureka, CA 95503
DSA File No. 12-C1 DSA Application No. Ol-Special
Dear Mr: smith:
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In accordance With your request ahd bur receipt 'of'documents 01fMay3~'2006,.the California
Geological Survey has reviewed the following engineering geologycbi1sulting report 'prepared
for the College of the Redwoods in Eureka; Califotnia:'
'Displacement Summary: Secondary Faults in the Little Sahilon Fault Zone, College of
the Redwoods Eureka Campus: LACO Associates Consulting Engineers, 21 W. 4thSt.,
P.O. Box 1023, EUreka, CA 95502; report dated May 2,2006, company project #6351.00,14
pages, 1plate.
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Although it is not stated in the above referenced report, we surmisethat conclusions presented in
the LACO Associates report are intendedto be used in designing mitigation of surface rupture
hazard to existing structures. at the Collegeof the Redwoods Eureka Campus that directly overlie
active "secondary" traces of the Little Sa1i:rlonFault (LSF). . We would like to begin our
discussion by stating that Califorma state law does not allow building new structures over active
faulttraces. The Alquist-PrioloEarthquakeFault Zoning Act of 1972alsoprohibits alterationof
structures that lie over active faults when the cost Qfthe alteration exceeds 50% bf the value of
the sti:i1cture.Having clearly stated the GGS .position that=avoidanceis:the b.est mitig~tihriffoi::
surface rupture hazard,. in the following paragraphs we will comment on the May 2,2006 LACO
Associates.repOrt.
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May, 2006
Review of Fault Displacement Estimate for
College of the Redwoods Eureka Cmnpus
DSA File No.
DSA Application No. Ol-Special
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The repoi:t SummariZes.an analysis in which measured fault offsets from trenches are used to:"
evaluate fue'potential"homoittal'ai1d'verticalcomponents bffuwre surface offsets caused by' :. ;";;
earthquakes"on.
the.-Littfe
S81m0nFault;-:The purpose :6fthe report is"neverelearlystated; nor are
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the"futended'uses~oHheresUlts:-ofthereport.describecLWithoutanimderstanding of the intended
'. purpose'"dftheanalysis and the intended uses of-the'report coIichisions',ifis difficult tQevaluate
the usefulness of the conclusions.
A few general comments and questions'-aboutthe report and analyses:
(a) will the users of the conclusionsof this report assume that"only
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. one "secondary" fault
will rupture to the surface in the next earthquake? It seems likely that movement will occur on
many of the faults in the hanging wall of the Little Salmon Fault in a future large earthquake.
(b) one of the assumptions the report authors make is that "Displacements are
independent of each other." This is likelynot true either looking backward in time ([a] many of
the features measured in trenches might have formed during just a few earthquakes, and [b] the
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magnimdeof individualdisplacementscausedbythe same.earthquakeareprobably correlated)or
looking to the future (wouldn't multiple instances of deformation in the hanging wall of a Little
Salmonfaulte~quake be expected?).. Thus,the compilationof offsetmeasurementsis,useful
in describing the range of offset alongpast "secondary" surfacerupfuies,.but the statistical
analysis is not as useful.
(c) no analysis of the potential folding or warping is proVided. However, the "Fault
locations &;projections-.map"".providedshowsmultiple.foldsor warps near the buildings aI14.the
report states that foldirigis likely.to occur:concurrently.with,movementofthe~SF. WIU_
mitigationforfoldingand/orwarpingalsobeproposedby the projectdesigners?
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(d) why are fault displacements resolved into horizontal and vertical components? Is the
intention of the project designers to sumthe 1.5 feet horizontal and 0.8 feet vertical vectors, and
to riUtigatefor 1.7 feet of displacement? If so, what is the likely orientation of the fault (both
s1Pke and dip) that will accommodate this displacement?
(e) why are the displacements that are estimated thought to have occurrences of seven and
12 percent in the next 11,000 years? The probability of occurrence information is based on
displacements measured in trenches and does not include a tempoial component. The
displacements measured may all have formed in the last several Little Salmon fault earthquakes,
a much shorter interval than the last 11,000years. The average recurrence interval given for
Little Salmonfault earthquakes is 268 years, shouldn't this (or the slip rate) factor into the
analysis if statements about the likely displacement over a given timeperiod are to be made?
(t) the report concludes with estimates of the likelihood that displacements of certain
~tudes
will occur. Is there any wayto assess the likelihood that these displacements will.
intersect the building footprint?
(gtthe ~stimated displacements are assumed to be pure dip-slip,however, if
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disp!acement:S)i!.~Iu,<!e
cp1obliquecomponentthenthe ma£111tllde
of slipwill be greaterthanthat
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estiri1at~&,:,:'What.iS.
the' evidence that future displacements will be exclusively dip:sfip~~Qt.",
altemativ~ly~.w~finagmtude of oblique slip should project designers cop.sid~1>laUSlble?~:'f':-'
(h) the report concludes by using "the observed extreme value of 1:Tfeet of app~en1\ '<-.
offset that projects through the former Librarybuilding" and an estimate 6fthe'probability'of '.~'.
occurrence is developed for this extremevalue. However, offsets of 7 feet in trench 1~8;'C(in 2'
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Review of Fault Displacement Estimate for
College of the Redwoods Eureka Campus
DSA File No.
DSA Application No. 0I-Special
May, 2006
or 3 events, which translates to 3.5102.3 feet of offset per event}and:other~~arly
large
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numbers ar~ givenn.l'Tablej.
WhY i$theJ.7.fe~t.estim~~ecop.sid~!,~~ ~ ~'ex.tremevalue'~?: .~'.."
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_ (i) l1as '«ons.t:r:q~tion .Q.f.
a:baI~W~~d..cros~)~ctt.()n.p.e.en..c.()~ider~d~' !fasufficientIy
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constrained
cross'
section
using
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. .' .. trench
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it might be possible to estimate future siilgle event .displacementson the "secondary faults~'.that
underlie the buildings.
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The conclusions reached in this short report are not well constrained and their intended uses are
not described. In order for project designers to appreciate the complexity of the natural setting
and the consultant's ~ysis, we'suggest that a clear description of the expected application of
the results of this analysis be provided. Additionally, a more complete description of the
range and style of deformation in the hanging.wall of the Little Salmon fault during a large
earthquake should be provided to project designers. For example, (a) what are the ranges of
surface faulting magnitudes and orientations that might be expected, (b) will more than one
"secondary fault" rupture the surface within the building footprint; and (c) will the faUltingbe
accompanied by foldiD.gor warping, and if so, what will the magnitude and direction of this .
folding be? The rate at which the estimated displacements might be expected to occur in time..
does not seem to be correctlypresented. Generally the data compiled in Table 1of the LACQ. .
report is useful, but the statistical analysis is not robust and is pqtentially misleading. We urge
that the questions posed and comments provided in this letter be addressed and also recommend
that 'extensive discussion take place between.the project.geologists,.project designers and:DSA to
ensure 1fui.ttherange of possibilities for surface deformation during future.Little Salmon fault.
earthquakes is understood by all.
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If you have any further questions about this review letter; please telephone the California
Geological Survey at (650) 6886367 (Knudsen) or (916) 445-5488 (Thornburg).
Respectfully submitted,
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Keith L. Knudsen
Senior Engineering Geologist
PG 6202,CEG2042
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Review of Fault Displacement Estimate for
College of the Redwoods Eureka Campus
May, 2006
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DSAFileNo.
. DSAApplicationNo.01-Special
Enclosures:
Copies to:
Joe POITaS, Director of Facilities
College of the Redwoods, 7351Tompldns Hi1lRoad, Eureka, CA 95503
Joseph R. Sutton, PriricipaI .
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DASSE DesigriInc., Structural Engineers, 33 New Montgomery Street, Suite 850, San Francisco, CA,
94105
Frank Ralph Bickner,
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LACOAssociates, 21 W. 41hSt; P.O. Box 1023 Eureka, CA 95502
Nat Cb:mban, Manager
Division of the State Architect, San Francisco Bay Area Regional Office, 1515 Clay Street, Suite 1201,
Oakland, California 94612
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