guidelines eq

7/31/2019 Guidelines EQ

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GOVERNMENT OF INDIA

CENTRAL WATER COMMISSION

GUIDELINESFORPREPARATIONANDSUBMISSIONOF

SITESPECIFICSEISMICSTUDYREPORTOFRIVERVALLEYPROJECTTO

NATIONALCOMMITTEEONSEISMICDESIGNPARAMETERS

SecretariatofNationalCommitteeonSeismicDesignParametersFE&SADirectorate,712(S),SewaBhawan,R.K.Puram

NewDelhi110605

(October2011)

NCSDPGuidelines:2011


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CentralWaterCommission


FOREWORDMinistry of Water Resources had constituted a high level interdisciplinary official body, the

NationalCommitteeonSeismicDesignParameters (NCSDP) forRiverValleyProjects in1991(formerly known as Standing Committee) to recommend the site specific design seismic

parametersfordesignofdamsandotherappurtenantstructuresoftherivervalleyprojects.The

site specific reports for determination of seismic parameters involve estimation of seismic

parameters either using the deterministic seismic hazard analysis (DSHA) method or the

probabilistic seismichazardanalysis (PSHA)method.Sinceboth theapproacheshave theirown

strengths andweaknesses, they are required to be used in combination to arrive at themost

appropriateengineeringdecisions. Itmaythusbeadvisabletoprovidetheresultsfromboththe

approachesandtheCommitteemaytakeaview ineveryparticularcase.Therefore,anattempt

hasbeenmade to formulate a document: Guidelinesfor Preparation and Submission of SiteSpecificSeismicStudyReporttoNationalCommitteeonSeismicDesignParameters(NCSDP)forRiverValleyProjects,tohaveingeneral,auniformapproachbydifferentexpertorganizationsforcarryingoutsitespecificseismicstudies.Astheinputdataontectonicfeatures,pastseismicityand

strong groundmotion characteristics required for such studiesare scanty inmany cases, these

guidelinesshallgoalongwaytoovercometheselimitationstilltherequiredinformationbecomes

availableintimestocome.

Iexpressmysincere thankstoall thepresentandExMembersofNCSDP,officers fromCWPRS,

Pune, IIT,RoorkeeandCWCfortheir invaluablecontributionandcooperation inhelpingCWCto

preparetheseguidelines.

For thismeticulouswork, Iexpressmygratitude forsincereanduntiringeffortsmadebyDr ID

Gupta,Director,

CWPRS,

Pune,

Dr

H

R

Wason,

Prof

&

Head,

DEE,

IIT

R,

Dr

M

LSharma,

Prof

IIT

R,

ShriManishShrikhande,AssociateProf,IITR,ShriCSMathur,ChiefEngineer(DSO),CWC,DrBRK

Pillai, Director, CWC and Shri S S Bakshi, Director, CWC & Member Secretary NCSDP for

formulationoftheseGuidelines.Iamalsohappytoacknowledgethesupportandcooperationof

officersandstaffofFE&SADirectorateofDamSafetyOrganization,CentralWaterCommissionin

preparationofthisdocument.

IamsurethattheseGuidelineswillbehelpfulforthedesignsofvariousrivervalleyprojectsofthe

country.

NewDelhi

October,2011


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ContentsPageNo.

Abbreviations1.0 Scope 1

2.0 GeneralConceptsandGuidingPrinciples 2

3.0 DataRequirements 5

4.0 Methodology 7

5.0 RecommendationsonDesignApproach 17

6.0

Submissionof

Study

Report

for

NCSDP

Approval

19

7.0 PresentationofStudyReportBeforeNCSDP 20

AnnexureA

IllustrativeExample:DSHAMethodforDevelopingTargetResponseSpectra 21AnnexureB

IllustrativeExample:PSHAMethodforDevelopingTargetResponseSpectra 23AnnexureC

ProformaforSubmissionofStudyReporttoNCSDP 27AnnexureD

Bibliography 29


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ABBREVIATIONS

DBE DesignBasisEarthquake

DSHA DeterministicSeismicHazardAnalysis

ICOLD InternationalCommitteeonLargeDams

IS IndianStandard

LET LocalEarthquakeTomography

MCE

MaximumCredible

Earthquake

MCM MillionCubicMeters

MPa MegaPascal

MT Magnetotellurics

NCSDP NationalCommitteeonSeismicDesignParameters

NGA NextGenerationAttenuation

OBE OperatingBasisEarthquake

PGA PeakGroundAcceleration

PSHA ProbabilisticSeismicHazardAnalysis

Sa Spectralacceleration

SEE SafetyEvaluationEarthquake

SGM StrongGroundMotion

SSZ SeismicSourceZones


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NCSDPGuidelines:2011 Page1

GUIDELINESFORPREPARATIONANDSUBMISSIONOF

SITESPECIFICSEISMICSTUDYREPORTOFRIVERVALLEYPROJECTTO

NATIONALCOMMITTEEONSEISMICDESIGNPARAMETERS

1.0

SCOPE

1.1 Theseguidelinesdealwiththepreparationofsitespecificseismicstudyreportofarivervalley

projectanditssubmissiontotheNationalCommitteeonSeismicDesignParameters(NCSDP)

fornecessary approval. The guidelineswill help in estimationof parameters tobe used in

seismicdesign,analysisandsafetyevaluationofneworexistingdamsandtheirappurtenant

structures. It isalsoexpectedthattheguidelineswillbringuniformity insitespecificseismic

studiesbeingcarriedoutbydifferentexpertorganizations.

1.2 The site specific seismic studies need tobe carried out and submitted for the approval of

NCSDP in respect of all such river valley project/dams that are classified under high or

extremehazardpotentialcategories.However, theuniformhazardpotentialcategorization

criteriafordams inIndiaareyettobeformulatedandapprovedbytheNationalCommittee

on Dam Safety. Till such time the hazard categorization criteria is not in place, it will be

mandatory, for the large dams1 that fall in seismic zone III, IVorV to get the approvalof

NCSDP forsitespecificseismicstudies fortheassessmentofdesignearthquakeparameters.

However,fortheprojectsinseismiczoneII,theapprovalofNCSDPforthesitespecificseismic

studieswillbemandatoryforsuchdamsthataremorethan30metersinheight.

1.3 The basic provisions of the guidelines are applicable for the river valley projects and its

appurtenantsstructures,andalsoforthepowerhouseandsuchotherstructureslocatedinthe

vicinityofdamwhosefailurecanresultinanuncontrolledreleaseofwaterfromthereservoir.Thetermdamusedhereshallmeananyartificialbarriermeanttoimpoundordivertwater,

and is inclusive of gravity dam, arch dam, embankment dam, barrage, weir, bund etc.

However, theprovisionsof theguidelinesneednotbeapplied incaseofprojectcanalsand

canalstructures,andalsonotincaseoftemporarystructuressuchascofferdams.

1.4 There isno intrinsicdifference in themethodology of selecting earthquake parameters for

design of new dams or safety evaluation of older dams. The rehabilitation of existing

structureswhicharedesignedonthebasisofstandardearthquakeprinciplesmaynotcallfor

fresh site specific seismic studiesunlessnew seismic activity are reported inor around the

project

sites.

However,

rehabilitation

cases

involving

dams

that

are

not

investigated

or

designedasperthemodernengineeringpracticesmayrequiresitespecificseismicstudies.

1.5 Thesitespecificseismicstudieswhicharenotmandatedasperaboveconditionsneednotbe

referredtoNCSDPunlessdirectedotherwisebyagovernmentorjudicialauthority.Inallsuch

exemptcases,theselectionofseismicdesignparameterswillcontinuetobegovernedbythe

IndianStandard1893(Part1)CriteriaForEarthquakeResistantDesignOfStructures2.

1Alargedamisonemorethan15mhigh(abovethedeepestfoundationlevel)oronebetween10mand15mhighsatisfying oneofthefollowingcriteria:

(a)

more

than

500m

long;

(b)

reservoir

capacity

exceeding

1x106

m3;

(c)spillway

capacity

exceeding

2000

m3/sec

2PendingfinalizationofParts2to5ofIS1893,provisionsofPartIwillbereadalongwiththerelevantclausesof IS1893:1984forstructuresotherthanbuildings


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1.6 Fordesigncriteriaotherthanthoserelatedtoseismicdesignparameters,referencemaybe

madetotheIndianStandardIS1893(Part1)3

.

2.0 GENERALCONCEPTSANDGUIDINGPRINCIPLES

The site specific seismic study for a river valley project requires an understanding of the

seismic scenario with regard to dam site, which includes geological setting of the area,

tectonic featuresand thehistoryofearthquakeoccurrence in theregion.Thestudyenables

evaluation of design ground motion based on identifiable seismic source zones and

appropriategroundmotionattenuationlaws.Thegeneralconceptsandprinciplesusedinsuch

studyaregivenbelow.

2.1 SeismicSourceZones

For the assessmentofdesignearthquake sourceparameters, it isnecessary to identify the

probableSeismicSourceZones(SSZ)wherecatastrophicruptureswillgenerateearthquakesat

a

site

in

prevailing

tectonic

environment,

and

adopt

a

pragmatic

approach

to

evaluate

the

likelymaximummagnitudeoftheeventwhichcouldoccurinfuture.

ThedelineatedSSZhastobeconsideredtorepresentazoneofstructural(tectonic)features

foroccurrenceoffutureearthquakes.TheprobablemaximumseismicpotentialoftheSSZ is

generallycontrolledbytheareaunderstrainbuildup,governingthelengthandbreadthofthe

seismicrupture,strengthanddeformationcharacteristicsoftherock,stressdrop,andfailure

mechanism.Theseismicpotential is rated in termsofthemagnitudeoftheevents,andthe

maximummagnitudethuscorrespondstotheprobablemaximumruptureparameters.Ifthere

are two, threeormore seismogenic featureswhichcan influence thegroundmotionat the

site,alltheseshouldbeconsideredaspotentialsourcesforthepurposeofanalysis.

Thedamagedue toearthquake isameasureof theearthquake intensityatany site,and it

dependsonthedistanceandenergyreleasedfromtherupturewithinSSZ.

2.2 DesignEarthquakes

2.2.1 Thelargestbelievableearthquakethatcanreasonablybeexpectedtobegeneratedbyspecific

seismicsources(SSZ)inagivenseismotectonicframeworkisreferredtoasMaximumCredible

Earthquake(MCE)forthatSSZ.Thisisthelargesteventthatcouldbeexpectedtooccurinthe

regionunderthepresentlyknownseismotectonicenvironment;andthestructuralsystem,if

designed on this basis, would prove to be highly uneconomical. Therefore a Design Basis

Earthquake(DBE),whichwouldhaveareasonablechanceofoccurrenceduringthelifetimeofthestructure,isalsoevaluatedkeepinginmindthedegreeofsafetyrequired.

2.2.2 Maximum magnitude of the events which could occur in a SSZ is evaluated from data on

earthquake occurrences. If data is available for sufficiently long duration, the highest

magnitudeof the knowneventofpastwith suitable increment is generally adopted as the

maximum magnitude of MCE for that source. For regions with poor documentation of

historicalevents,anappropriate increment isaddedtothehighestmagnitudeoftheknown

event for evaluation of MCE to account for the incompleteness of seismicity catalog The

deterministicapproachfordeterminationofMCEpractically ignoresthereturnperiodofthe

3ibid2


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event.TheMCE levelofgroundmotioncanalsobeevaluatedusinganappropriateapproach

similartothatgiveninICOLDbulletin89(revised).

2.2.3 TheDBE represents that levelofgroundmotionatdam siteatwhichonlyminorandeasily

repairable damage is acceptable. Since the consequencesof exceeding theDBE aremainly

economic, theoreticallyDBEshallbedetermined fromaneconomicanalysis.However, frompracticalconsiderations theDBE ischosen foracertain returnperiodofthegroundmotion.

For the occurrence of earthquake shaking not exceeding the DBE, the dam, appurtenant

structuresandequipmentshouldremainfunctionalanddamagesshouldbeeasilyrepairable.

2.2.4 IntherecentlyadoptedICOLDguidelines(SelectingSeismicParametersforLargeDams,2009),

theterminologiesofSafetyEvaluationEarthquake(SEE)andOperatingBasisEarthquake(OBE)

havebeenused inplaceofMCEandDBE.There isno intrinsicdifference inthedefinitionor

usageofOBEvisvisDBE.However, theusageof SEEhasbeen characteristicallydifferent

thanMCEonaccountofapplicationofaprobabilisticapproachwhereinthechoiceofreturn

periodofevent

islinked

with

hazard

potential

categorization

ofdam.

Change

over

from

MCE

DBEterminologiestoSEEOBEterminologies isconsidereddesirable;but,thesamehasbeen

deferredtilladoptionoftheuniformhazardpotentialcategorizationcriteriafordamsinIndia.

2.3 SeismicEvaluationParameters

2.3.1 Groundmotionatanysiteisinfluencedbysource,transmissionpathandlocalsiteconditions.

Thefactorsresponsibleforsourceeffectincludefaulttype,rupturedimensions,mechanism

anddirection,focaldepth,stressdropandamountofenergyreleased.Thetransmissionpath

effectrelatestothegeometricspreadingandabsorptionofearthquakeenergyastheseismic

wave travel away from the source; and the responsible factors include rock type, regional

geological structures including surface faults and folding, crustal inhomogeneities, deep

alluvium, and directivity effects (direction of wave travel vs direction of fault rupture

propagation).Thelocalsiteeffectresultsfromthetopographicandsoilconditionspresentat

thesite.

Groundmotioncanbecharacterizedbypeakvaluesofexpectedacceleration,velocity,and/or

displacement.Ideally,allfactorsaffectinggroundmotionshouldbeconsideredforevaluation

oftheseparameters;butthisisnotpractical.Generally,onesourcefactor(magnitude)anda

singletransmissionpathfactor(distance)onlyareconsidered.The localsiteeffectsareoften

disregarded, or limited to simple distinction between rock and alluvial sites and possible

considerationofnearfieldeffects.Empiricalrelationsderivedfromavailableearthquakedata(attenuation relations) relategroundmotionparameterstodistance from thesourceandto

magnitude.

2.3.2 Attenuation relations:Attenuation relations are empirical relationsdeveloped from Strong

GroundMotion (SGM)measurements, and areused for the predictionof expected ground

motionanditsintrinsicvariabilityattheprojectsite.Suchpredictions aregenerallyperformed

usinggroundmotionmodelsthatdescribe thedistributionofexpectedgroundmotionsasa

functionofafewindependentparameters,suchasmagnitude,sourcetositedistanceandsite

classification. The distribution of expected ground motions described by any one ground

motion model is given in terms of median spectral amplitudes and associated standarderror/deviationusuallyreferredtoasaleatoryuncertainty.Theseismichazardstudiesshould


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needtoaccountforboththeseuncertaintiesintherelations.

Ideally,theattenuationrelationtobeusedforaparticularsiteshouldbedevelopedusingthe

recorded strongmotion data in the region around the site of interest. However, due to

paucityofstrongmotiondata in India,such relationsarenotavailable fordifferentpartsof

the country. In practical engineering applications, it thus becomes necessary to identify

suitablerelationsfromthepublishedliterature.

2.3.3 Duration of shaking: The strong motion duration is important from the point of view of

responsebehaviorofthestructurebeingexamined,anditlargelydependsontheearthquake

magnitude and alsoon thedistance and site condition to some extent. The strongmotion

durationisafunctionofthefrequencyandrepresentsthesumtotalofthedurationsofallthe

strongmotion segments contributing 90%of the energyof completemotion (Trifunac and

Brady,1975).Durationofstrongshakingisanimportantparameterfordamsafetybecauseof

itsdirectrelationtodamages,especiallyincaseofembankments.

2.3.4 Responsespectrum:Theresponsespectrum representsthemaximumresponse (inabsolute

acceleration and relative velocity or relative displacement) as a function of natural time

period, for a given damping ratio, of a set of singledegreeoffreedom (SDOF) systems

subjectedtoatimedependentexcitation.

ItiscustomarytorepresentcomputedresponseofSDOFsystemtoaparticulargroundmotion

in the form of elastic spectra. These spectra show the response quantity (e.g. absolute

acceleration) against the natural periods of SDOF systems for different values of damping.

Sincetherearepeaksandvalleysinthespectrathuscomputed,thevagariesareironedoutas

faraspossiblebythesmoothenedspectra.ResponsespectrumcharacterizingtheMCEorDBE

hastobesitespecific.

Thenumberofdampingvalues forwhichresponsespectrashouldbespecified to represent

theMCEorDBElevelofgroundmotionshouldencompassarangeofvaluesapplicabletothe

typeofdamand levelofgroundmotionconsidered.Dampingvaluesforanalysisofconcrete

and masonry dams may be taken as 5 and 7 percent respectively when the response is

assumedtobepredominantlyelastic.Dampingvaluesfortheanalysisofembankmentdams

maybetakenas10to15percent.

2.3.5 Acceleration time histories: The seismic parameters in terms of peak values and spectral

characteristicsaresufficientforanalysisofmanydams.However,incaseofdamswithhighor

extremehazardpotentials,andforuseofnonlinearanalysistechniques,thespecificationof

earthquake motion in time domain (as acceleration time history records) is also required.

Accelerationtimehistoriesmaybespecifiedforhorizontaland/orverticalmotionandshould

preferablyberepresentedbyrealaccelerogramsobtainedforsiteconditionssimilartothose

present at the dam site under consideration. However, since strong ground motion data

currentlyavailabledonotcoverthewholerangeofpossibleconditions,this isessentiallyan

exercise in generation of random waveforms (keeping in view the duration of the ground

motion and the general pattern of ground motion history) which are synthetic in nature.

Severaltimehistoriescouldbegeneratedtomatchthesametargetresponsespectrum,and

allofthesewouldbeequallyacceptablefromthepointofseismicconsiderations.


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2.4 DeterministicandProbabilisticAnalysisApproaches

The two general approaches for developing the sitespecific response spectra are the

deterministic seismic hazard analysis (DSHA) and the probabilistic seismic hazard analysis

(PSHA) methods. The basic inputs required for both the approaches are the same, which

include data on past seismicity, knowledge of the tectonic features, geological and

morphological setup, geophysical anomalies, information on site soil condition and the

underlyinggeologyofthesurroundingarea,andtheattenuationcharacteristicsofthestrong

motionparametertobeusedforquantifyingthehazard.Thetreatmentofseismicitydatafor

homogenization,completenesswithrespect to timeandsize,anddeclusteringarerequired

beforeproceedingwithanyoftheapproaches.

2.4.1 In its most commonly used forms, the DSHA approach proposes design for the socalled

"scenario"earthquakes(MCE).Theunderlyingphilosophyisthat"scenario"earthquakeofthe

seismic source is scientifically reasonable and is expected to produce most severe strong

groundmotionatthedamsite.OneofthemostimportantissuesisthereliableestimationoftheMCE,foreachoftheidentifiedseismicsourcezones,onthebasisoftheavailabledataon

past earthquakes and the seismotectonic and geological features of a SSZ. However, the

delineationof theSSZ, theestimationofMCEmagnitudes,aswellas theestimationof the

corresponding ground motion at a certain distance from the earthquake source, are

commonlyassociatedwithlargeuncertainties.TheDBElevelofdeterministicgroundmotionis

generallytakenasanappropriatefraction(say0.5)oftheMCElevelofmotion.

2.4.2 ThePSHAapproachprovidesastructure inwhichuncertaintiescanbe identified,quantified

andcombinedinarationalapproachtoprovideacombinedeffectofseveralalternateseismic

sourceson

seismic

hazard

atasite.

Thus,

there

are

multiple

scenarios

and

models

for

hazard

analysisapplicableatagiven site.ThePSHAcarriesout integrationover the totalexpected

seismicitytoprovidetheestimateofagroundmotionwithaspecifiedreturnperiod.TheMCE

levelofgroundmotion isproposed tobedefinedwithareturnperiodofabout2500years,

whereasDBElevelofgroundmotionisdefinedwithamuchlowerreturnperiodofabout145

years.

3.0 DATAREQUIREMENTS

Theprimarydataforidentificationofpotentialsourcesofearthquakesandevaluationoftheir

characteristicspertaintothetectonic,geologicandseismicactivityconditionsat,and inthe

vicinityof,thedamsite.Thestudyshouldconsidertheregionalaspects,andthenfocusonthelocalsiteconditions,soastofullyunderstandtheoverallgeologicsettingandseismichistory

ofaparticularsite.

The below mentioned information need to be compiled by getting inputs from various

organization or institute and published standard literature for the assessment of seismic

designparameters.

3.1 RegionalGeologic/Seismotectonic Setting

Seismotectonic map: A seismotectonicmapof1: 1000,000or comparable scale,depictinggeology,structures(withemphasisonnatureandextentofmajorfaults,shearzonesetc)and

seismicity(asdetailedinpara6.2&7.1)foranareaabout300kmradiusfromdamsiteshould


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beused ( i.e.about60 latitudex6

0 longitudewiththedamsiteatthecentre).Locationand

descriptionof faultsand shear zonesandassessmentof the capabilityof faults togenerate

earthquakesshouldbe furnished.This should includedocumentationon theexistenceofor

thelackofhistoricalorprehistoricalactivity(paleoseismicity)foreachmajorfault.

Seismotectonicsection: At leastoneregionalseismotectonicsection throughthedamandacrossthemajortectonictrend(basedon6.1.1)oftheregionshouldbeprepared.Thesectioncoveringaminimum50kmreachoneithersideofthedamshouldclearlyshow(ifnecessary,

by vertical exaggeration) the subsurface disposition of the major faults and earthquake

hypocenters.

3.2 SeismicHistory

Earthquake catalogue: Theearthquake catalogue should contain informationaboutorigintime (date/ time), location (latitude/ longitude/ depth), and size (magnitude / type of

magnitude/ intensity)ofearthquake fromthehistoricaltimetopresent time foranareaof

about300kmradiusfromdamsite.ThisdatamaybeobtainedfromIMDandupdatedonthebasisofotherauthenticsources.Totheextentpossible,informationonfocalmechanism,felt

area,accompanyingsurfaceeffects,knownorestimated intensityofgroundmotion induced

atthedamsite,andthesourceofdataanditsreliability,shouldalsobepresentedforallmajor

events.

Micro earthquake investigations: Fordams exceeding the heightof 100m, thedetails ofmicroearthquakedata recordings around thedam sitewithin a radiusof50 km shouldbe

providedincorporatingfullcatalogueinformationforaperiodofatleastsixmonths.Suchdata

shouldbeobserved/collectedbytheprojectauthorities.

3.3 LocalGeologic

Setting

Geologicalmap: Fordamshigher than200mand located inseismiczone IVorV (asper IS1893 Part 1 (2002) a geologicalmap (based on photogeology/imagery studies and ground

mapping)on1:50,000to1:60,000scalesshouldbepreparedforanareaof50kmradiusfrom

the dam site with special emphasis on gross lithological (or stratigraphical/tectono

stratigraphic)domains,structuraldetailslikefaults,folds,shearzones,masterjoints,structural

trendlinesandlineamentsetc.Geomorphicand/orevidencefromQuaternaryGeology(ifany)

withintheinfluenceareaindicatingpresenceofactivefaultshouldbedocumented.Geological

evidenceswhereveravailableonthenatureofmovementalongthefaultvisvistheageof

such movement should be indicated. A short descriptive account on the various lithostratigraphicunitsandstructuralelementsshouldbeincluded.

Surfaceandsubsurfaceexploration:Thereportofexplorationshouldcontainlocalgeologicalmap(s)ofthedamsiteandotherappurtenantstructureson1:1000orlargerscalealongwith

topographiccontours.Thereportshouldalsoincludegeologicalsectionsalongandacrossdam

axisThegeologicalsectionsshouldbederivedthroughdrillingandothergeophysicalprobing,

andtheyshouldshowdepthtooverburden,faults,shearzonesetc.Thecompressionalwave

velocity (Vp)andshearwavevelocity (Vs)ofat least30mbelow themajorstructures (dam,

powerhouseetc.)shouldbeprovided.


11/34



Additionalinputsonsubsurfaceconfigurationofmajorfaults: Fordamsofheightexceeding200 m and located within seismic zone IV or V, additional inputs on the subsurface

configurationofmajorfaultswithin50kmradiusofthedamsiteshouldbeprovidedbasedon

Local Earthquake Tomography (LET) / Magnetotelluric (MT) studies or any suitable

methodologymaybeadopted,detailsofwhichshouldalsobefurnished.

4.0 METHODOLOGY

The site specific seismic design parameters will depend on many variable factors. It is an

extremelydifficulttasktodeterminetheexactparametersinviewofuncertaintiesrelatedto:

[a] choice of earthquake parameters (namely magnitude, distance, focal depth and

mechanism)relatedtoMCEandDBE;[b]choiceofgroundmotionattenuationrelationshipfor

computing spectral accelerations and [c] the elastic modulus, shearmodulus and damping

characteristics of the material used in construction. In view of above, it is important to

exerciseajudiciousbalance invarioussteps involved inthestudy.Thementionedguidelines

beloware

expected

to

facilitatethis

process

for

the

meaningful,

reliable

and

safe

design

of

rivervalleyprojectsinthegivenseismicenvironment.

4.1 SelectionofEarthquakesforAnalysis

All geological maps and data (as specified in section 6) should normally be studied to

determineactiveseismicfeatures.

A tablegiving the listofearthquakeswithperiodwisebreakup (historical to1900;1901 to

1963;1964topresent)shouldbeprepared.Forearthquakedatasubsequentto1964,thetype

ofmagnitude (i.e.MW,Ms,mb,ML,MDetc)and focaldepth shouldbegiven; the aand b

values from GuttenbergRichter (GR) relation should be calculated through regression

analysis,preferablyusingmaximumlikelihoodmethodandtheMmaxforaspecifiedrecurrence

periodshouldbe indicatedusingaand bvaluesforeach identifiedseismicsourcezoneas

wellasfortheregionasawhole.

Theappropriatedistanceconsistentwithattenuation relationship frompostulatedscenario

earthquake from dam site should be tabulated. Efforts should be made to classify the

correspondingfaultsbasedon itstypesofmovement(i.e.normal,thrust,strikeslip[dextral/

sinistral])visvisthelocationofthestructure(e.g.,hangingwall,footwall,directivityincase

of strikeslip etc.). A floating earthquake approach should be adopted where seismogenic

featuresinthevicinityofdamsitearenotknown.

4.1.1 Magnitude of MCE: TheMCE for aparticular SSZ canbe estimated from the catalogueof

earthquakes in the area of 300 km radius around the dam site (i.e. about 60 latitude x 6

0

longitude with the dam site at the centre), using several different methodologies. The

magnitudeforMCEcanbeestimatedusingmethodsasunder:

incrementingtheworstrecordedearthquake,toaccountforincompletenessofcatalogusingaandbvaluesofGuttenbergRichterrelationshipextremevaluedistributionusingempiricalrelationship


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predictingmagnitudeofearthquakebasedonfaultrupturedimensions4Thesimplestmethodistosuitablyenhancetheworstrecordedearthquakebyanappropriate

incrementtoaccountforincompletenessofdataforarrivingatMCE.

4.2 SelectionofAttenuationRelations

HavingchosenthedesignearthquakeparametersofMCEorDBEshock inrelationtoproject

site, thenext task is toobtain thegroundmotion characteristicsat the siteusingempirical

groundmotionmodels(attenuationrelations)whichrelatetheresponsespectralamplitudes

atdifferentnaturalperiodsor frequenciesof the structure to thegoverningparameter like

earthquakemagnitude,sourcetositedistanceandsitegeologicalconditions.

The selectionof appropriate groundmotionmodels for aparticular target area from large

numberofpublished attenuation relations forother regions isnot thateasy.The selection

process becomes complicated because there may be systematic differences in terms of

seismicsources,wavepropagationorsiteresponsebetweenthetargetregionandhostregion

fromwherethedatausedtoderivethemodelwasobtained.

The goal is to identify the smallest setof independentmodels (outof the largenumberof

modelsavailableinpublishedliterature)thatcapturetherangeofpossiblegroundmotionsin

the region under study. The criteria recommended for shortlisting the ground motion

predictionmodel,arrangedintheorderofdescendinghierarchy,areasunder:

Modelshouldbeforasimilartectonicregimeasitwouldclearlynotbeappropriatetouseanequationderivedforasubductionzoneforhazardanalysisinaregionofcrustal

seismicity,andviceversa.

Model ispublished inan internationalpeerreviewedjournal.Thepeerreviewprocessusuallyensures that themodelsareclearlydescribedand thatbasic tests (analysisof

residuals, comparisonwithprevious studies, etc.)havebeenperformed. Themodels

whichhavebeenextensivelyusedandtestedshouldbefavoured.

Documentationofmodeland itsunderlyingdataset shouldbecomplete.Theoriginaldatasetusedinthestudymustbepresentedinthepublicationandthedataprocessing

mustbedescribedandtheparametersusedinregressionstabulated.

Frequencyrangeofthemodelshouldbeappropriateforengineeringapplications.Forsomeengineeringapplicationswherehighfrequencies(>10Hz)or lowfrequencies(


13/34



SometypicalattenuationrelationsbeingusedarelistedinBibliography.

The choice of any particular attenuation relationship should be explained with complete

references and narration of itsmerits. Further, the final selection should be based on the

rankingcriteriaduetoScherbaumetal.(2004)usinglimitedstrongmotiondata,ifavailablein

theregionofinterest.Forthispurpose,itisproposedtodividethecountryintothreeregionsfortheidentificationofseparatesetsofattenuationrelationshipsthatarebestsuitedforeach

region.Thetargetedthreeregionsare(i)Himalayas,(ii)Gangabasinand(iii)Shieldregions.

Such anexercisewill call fordetailed examinationof the geophysical criteria regarding the

degreeofsimilarity,orotherwise,betweenthehostregionsfromwherethecandidatemodels

havebeenderivedandthethreetargetregions.

Till the detailed study is carried out to identify the attenuation relations for the above

mentioned threeregionsof India,the following informationmaybeconsidered forthetime

being:

The spectral acceleration values computed at various natural periods from differentpublished attenuation relations when compared with the limited observed spectral

amplitudesfromafewHimalayanearthquakes,therelationshipsduetoAbrahamsonand

Silva(1997)andTrifunacandLee(1989)areseentohavetheoverallbestmatchingwith

theobserveddataandmaythusbeconsideredsuitablefortheHimalayanregion.

Abrahamson and Silva have recently updated their relationship as a part of the NextGeneration Attenuation (NGA) project using the PEER NGA database. The updated

relationshiphasincludedthefaultdirectivityandsiteeffectsmorecomprehensively,but

itneeds exact information about the fault rupture geometry,which isnot available in

most cases. TheotherNGA relations alsoneed informationon faultdetails to varyingextent. Hence the NGA attenuation relations cannot be used without making some

subjectiveassumptions leadingtobiasedresults.TheearlierrelationofAbrahamsonand

SilvamaythereforehavetobeusedfortheHimalayanRegion.

Based on world wide data, Graizer and Kalkan (2009) have proposed an approach toobtaintheresponsespectralshapeconsideringthedependenceonmagnitude,distance,

and site condition which can be scaled by the PGA. They have also developed an

attenuation relation for PGAusing the samedatabase (Graizer and Kalkan, 2007). This

approach is also considered suitable for the Himalayan region, because the PGA

attenuationofGraizerandKalkan (2007) is found todescribe theavailablePGAdata in

Himalayanregionquitewell

The relationshipdue toTrifunacandLee (1989)hasconsidered thedependenceon themagnitudeanddistance inaphysicallyrealisticway inthat themagnitudeanddistance

saturationeffectsaswellasthegeometricspreadingwithdistanceareaccounted forat

each frequency. Also the influences of both the shallow local soil, as well as deep

geological formationsat the site,are included in this relationship.Asno strongmotion

data isavailable for the IndoGangeticplains, the relationshipof Lee isproposed tobe

used for the region due to physically realistic dependence on various governing

parameters.


14/34



4.3 DevelopmentofTargetResponseSpectra

Forestimatingthesitespecificdesigngroundmotionbydeterministicaswellasprobabilistic

approach, it is first necessary to obtain the response spectra of horizontal and vertical

componentsofmotionseparately foradampingratioof5%.Suchspectraareknownasthe

target response spectra, and the ground motion acceleration time histories required fordetailed dynamic response analysis are generated synthetically to be compatible with the

target response spectra.Response spectra forother valuesofdamping are then computed

from these acceleration time histories. Target response spectra can be developed by the

followingthreeapproaches:

(i) ScalingastandardspectralshapebyPGA:

Theresponsespectraofhorizontalandverticalcomponentsofgroundmotioncanbeobtained

conveniently by scaling a mean plus one standard deviation normalized spectral shape

appropriate for thesiteof interestwiththemedianpeakgroundacceleration.Thestandard

spectralshapeshouldbebasedonsufficiently largeensembleofstrongmotionrecordswithmagnitude and sourcetosite distance close to the desired magnitude and distance of

controllingMCE.ThePGAcanbeestimatedbydeterministicorprobabilisticapproach.

(ii) Usingspectralamplitudeatselectedperiods(say0.2and1.0sec):

Theresponsespectralamplitudesatnaturalperiodsof0.2secand1.0secalongwithPGAcan

be estimated using an appropriate attenuation relation from deterministic or probabilistic

approach. Median or median plus one standard deviation values (depending upon the

seismicityoftheregion)ofalltheseparametershastobeusedinthedeterministicapproach

andwithareturnperiodof2500years intheprobabilisticapproachtogettheMCE levelof

spectra.

The control period T2 which marks the beginning of the constant velocity range is then

obtainedastheratioofthepseudospectr ac ionat1.0and0.2secasfollowsal celerat

T S 1.0sS 0.2s5

:

x 1sThecontrolperiodT1whichmarksthebeginningofconstantaccelerationrangeisobtainedas

afractionofT2dependingonthesoilclassific tion s:a a

T 12 to 15 x Twiththefactor1/2correspondingtoverysoftsoiland1/5correspondingtomassiverocks.For

mostoftheprojectsitestheactualfactorwillbebetweenthesetwoextremevalues(0.20.5).

Thepsuedospectralacceleration isconsidered to increase linearly fromPGAvalueatperiod

T0= 0.03 sec to its maximum value at T1. The maximum value of the psuedospectral

accelerationobtainedatTn=0.2secisheldconstantfromperiodT1toT2.Forperiodslessthan

5P K Malhotra- Return period design ground motions. Seismological Research Letters, 76(6):693-699,2005.


15/34



T0thepsuedospectralaccelerationisconsideredtobethesameasthePGA.

The psuedospectral velocity is held constant at ST STx in the range fromperiodsT2toT3.Theconstantvelocityrange isconsideredtoextenduptoT3=(6to9)T2 ,

withthefactor6correspondingtomassiverocksand9correspondingtoverysoftsoil,afterwhichtheconstantdisplacement(orlinearpsuedospectralvelocitywithnegativeslope)range

begins.Forstrongearthquakes,theconstantdisplacementrangeoftheresponsespectrumin

the near field generally begins between 3sec and 4sec. The constant psuedospectral

displacementisobtainedfromthepsuedospectralvelocityatT3as

ST ST x T2 ST x T2 x T2Thetripartiteplotofresponsespectrumisshowninfig1

Figure1:Responsespectrumtripartiteplot(logscale)


16/34



The tripartite format of design spectrum is not very convenient to use in practice and

therefore,itisnecessarytotranslateitintoalinearplotofpseudospectralacceleration(Spa)

versusnaturalperiod (T).Foraresponsespectrum intripartite format (asshown inFig.1),thepseudospectralacceleration(S)maybep as nctionofthenaturalperiod(

T)as:

rescribed afu

ST PGA x

1 ; T TT T ; T T TA ; T T TV T ; T T TD T ; T T

Theparameters ,A,VandDaredescribedasbelow:

1;

A ;V 2 x D 2 x T x STPGA

;

Thepseudoaccelerationdesignspectrumspecifiedbytheaboveequationandcoefficients is

shown in Fig.2. Thepositionsof the controlperiodsof theequationhavebeenmarked in

thesefigures.Itmaybeseenthatwhilethepseudoaccelerationspectrumplotinlinearscale

hasdifferentcurves,thetripartiteplotinlogarithmicscalesiswelldefinedbyasetofstraight

linesbetweendifferent pairsof control periods. Therefore, the above equation of pseudo

accelerationdesignspectrum isderivedfromthecorrespondingequationsofstraight linesof

pseudovelocityspectrumonthetripartiteplot.

Figure

2

:

Pseudo

spectral

acceleration

(linear

scale)


17/34



(iii) Usingfrequencydependentattenuationrelationships:

TheattenuationrelationsusedforestimatingthePGAorspectralamplitudeat0.2and1.0sec

intheabovetwomethodsaregenerallydefinedforalargenumberofnaturalperiodscovering

the entire frequency range necessary to define the complete response spectrum. Thus, by

estimatingthespectralamplitudeatallthenaturalperiodsforwhichtheattenuationrelation

is defined, it is possible to obtain the complete response spectrum without making any

assumptions. This can be done by using both deterministic as well as probabilistic

methodologies.

4.3.1 DSHAMethodologyforDevelopingTargetResponseSpectra

Incommonlyuseddeterministicapproachfordevelopingtheresponsespectraforadamsite,

onehastofirstassessthemaximumpossibleearthquakemagnitude foreachof theseismic

sources (important faults, shearzones, thrustsetc) in theprojectareaof interest (generally

about 60 latitude x 60 longitude with the dam site at the centre). Such an earthquake is

commonly termedasMaximumCredibleEarthquake (MCE),which isthe largestearthquake

thatcanbesupportedbyeachsourceunderthesitespecificseismotectonicframework.The

MCEforeachseismicsourceisthenpresumedtooccurata locationthatplacesthefocusat

theminimumpossibledistance to theprojectdamsitewhich thesourcegeometrypermits.

TheresponsespectraforeachMCEcanthenbedevelopedusinganappropriateattenuation

relation. The zeroperiod spectral value is the peak ground acceleration, i.e., zeroperiod

spectralacceleration (ZPA)=PGA.Theworstcombinationof themagnitudeanddistanceof

MCEisnormallyconsideredtogettheMCElevelofdesigngroundmotion.

ThetargetspectrumforMCEconditionmaybetakenasatmedianplusonestandarddeviation

levelforprojectsitesinregionsofhighseismicity(SeismicZoneIVandVasperIS:18932002)

becauseofrelativelyshortreturnperiodsoflargeearthquakesandtoaccountforthescatter

in recordedearthquakedata.For the low seismicity regions (Seismic Zones IIand IIIasper

IS:18932002), the recurrence intervalofMCE levelearthquakes isvery largeand therefore

theMCEtargetspectrumforprojectsitesintheseregionsmaybetakenasmedianestimates.

Thisistomaintainapproximatelyuniformlevelofseismicriskacrosstheentirecountry.

ThetargetresponsespectraforDesignBasisEarthquake(DBE)conditionmaybetakenasone

standard

deviation

less

than

the

corresponding

MCE

target

spectra,

or

half

of

MCE

target

spectra,whichevergivehigheramplitudeatnaturalperiodofinterest.

AnillustrativeexampleoftheforegoingmethodologyisgiveninAnnexureA4.3.2 PSHAMethodologyforDevelopingTargetResponseSpectra

Theprobabilisticseismichazardanalysis(PSHA)approach isbasedonanaltogetherdifferent

philosophy and concept compared to the deterministic seismic hazard analysis (DSHA)

approach for arriving at sitespecific design earthquake ground motion for important

engineeredprojects.TheDSHAaimsatestimatingthepossiblemaximumvalueoftheground

motion

amplitudes

by

considering

a

maximum

magnitude

of

earthquake

to

occur

at

the

shortestsourcetositedistance, irrespectiveoftheprobabilityofsuchanoccurrence,which


18/34



remains unknown and unquantified. The PSHA on the other hand aims at estimating the

groundmotionamplitudeshavingadesiredannualprobability(p)ofexceedanceduetoanyof

theearthquakesexpectedtooccuranywhereintheregionaroundtheprojectsite.Thereturn

periodTr (years) isequal to reciprocalof the annualprobability (p)ofexceedance.Thus, a

probabilityof exceedance equal to 0.001 represents a return periodof 1000 years for the

groundmotion.TheICOLDguidelines(2010)specifythereturnperiodsof10,000years,3,000

yearsand1,000yearsfortheMCE levelofgroundmotionfordamswiththreedifferentrisk

levels to the downstream population. The PSHA approach can also be used to obtain the

return period corresponding to the deterministic estimate of the ground motion for

comparison with the return periods proposed by ICOLD guidelines and taking appropriate

decisionsaboutthesuitabilityofthedeterministicestimate.

Detailson the currentlyusedPSHAapproach canbe read fromCornell (1968),EPRI (1987),

Reiter(1990),SSHAC(1997),USACE(1999),Gupta(2002),McGuire(2004),etc.ThebasicPSHA

approachisbasedoncomputingthefollowingannualprobabilityofexceedanceofaspecifiedmeasureofthegroundmotionamplitude(e.g.theaccelerationresponsespectrumamplitude

SA(T)atnaturalperiodT):

Here,istheannualprobabilityofexceedingaspectralamplitudeSA(T)duetoanyofthe earthquakes in any of the source zones, n (, ) is the annual occurrence rate ofearthquakesofmagnitudeatsourcetositedistanceineachoftheseismicsourcezonesaround the project site, and

| , is the probability of exceeding the spectral

amplitudeSA(T)duetomagnitudeanddistancecombination(,) inthenthsourcezone.Theplotof SA(T)vsisknownastheHazardCurve.Bycomputingthehazardcurvesforall thenaturalperiodsT, thedesign response spectrum canbeobtainedwithadesired

annualprobabilityofexceedance(orrecurrenceperiod)atalltheperiods.Suchaspectrumis

knownasUniformHazardResponseSpectrum.

1 | , . ,

The various steps involved in computing the hazard curves to implement the PSHA

approachcanbesummarizedasbelow:

Step1:DelineationofSeismicSourceZones

Thefirststep inPSHA isto identifyanddelineatevariousseismicsourcezones(SSZ)withina

regionof6lat6longwiththedamsiteatthecenter,whereaSSZrepresentstheportion

of earths crustwith distinctly different characteristics of earthquake activity ( in terms of

frequency&maxpotential) from thoseof the adjacent crust.Though fault specific seismic

sourcescanbeusedinsomecases,duetolackofclosecorrelationofobservedseismicitywith

knownfaults,extendedareatypeofsourcesisusedmorecommonlyinpracticalapplications.

Itmaybe noted thatdelineation of seismic sources cannotbe considered free from some

elementofsubjectivity.


19/34



Step2:EstimatingSeismicityofaSourceZone

TheGutenbergandRichters(1944)recurrencerelationship log ,whereN(M)representsthecumulativenumberofearthquakesperyearwithmagnitudeMorgreater, is

fitted toeach seismic source in step 2using availablepastearthquakedata.The catalogue

datamaybetreatedforremovalofforeshocksandaftershocks,homogenizationofmagnitudetoeitherMworMsandcorrection for incompleteness in sizeand time.This is thenused to

obtaintheoccurrenceraten()ofearthquakesinmagnitudeinterval( ,+ )bydiscretizingthecompletemagnituderangebetweenaminimumthresholdmagnitudeandthe

maximum upper bound magnitude. These numbers are finally distributed over the entire

source zone by dividing it into a large number of small size elements to get the annual

occurrence rate (, ), where refers to the distance to the center of the ith sourceelement.

Step3:EstimationofProbabilityqn[SA(T)I

,

]

An attenuation relationship suitable for the region of interest is selected in step 3,which

describestheresponsespectralamplitudes intermsofearthquakemagnitude,sourcetosite

distance, and site geologic condition. Such a relation is able to provide the least squares

medianestimateandthecorrespondingprobabilitydistributionoftheresidualsforspecified

earthquake magnitude and sourcetosite distance , which can readily be used toestimate the probability qn[SA(T) IM,R ].A single attenuation relationmay normally beapplicabletoallthesourcezones,butdifferentrelationsmayalsobeused,ifnecessary.

Step4:ComputationofUniformHazardSpectrum

The fourth and the final step in the PSHA approach is to compute the hazard curves, i.e.probabilitydistributionp[SA(T)],bycarryingoutthesummationsoverallthemagnitudesand

distances in all the source zones. A uniform hazard response spectrum is obtained by

computing the p[SA(T)] for all the natural periods of interest and estimating the

correspondingspectralamplitudeswithadesiredannualprobabilityofexceedance(orreturn

period).

AnillustrativeexampleoftheforegoingmethodologyisgiveninAnnexureB

4.4 DeterminationofSitespecificSeismicCoefficients

With theknowledgeof thenaturalperiodof thedam section, the response spectra canbe

used toobtain thesitespecificseismiccoefficients.The typeandpreliminary sectionof the

dam,thecomputational formula,andotherassumptionmade inthecomputationofnatural

periodshouldbefurnishedinthestudy.

4.4.1 Horizontalseismiccoefficient:Forthecomputednaturalperiodofthedamsection,findthe

spectralamplitudeforDBEusingthe5%dampedspectrumfortheconcrete/masonrydamand

10%damped spectrum forearthenand rockfilldams.Thehorizontal seismic coefficienthmaybetakenasafraction(say0.5)ofthespectralamplitudeobtainedasabove,howevernot

lessthanthatobtainedasperIS1893(1984).


20/34



4.4.2 Vertical seismic coefficient: Similar steps (as for h) should be applied on the response

spectrum for the vertical seismic component for the determination of vertical seismic

coefficientv.Thealternativeapproach (asper IScode)shouldalsobeappliedwherein the

verticalseismiccoefficientistakenas2/3rdsofthehorizontalseismiccoefficient(i.e.v=2/3

h).Thehigherofthetwovaluesshouldbetakenasthedesigncoefficient.

4.5 EstimationofDurationofShaking

Thedurationof strong shakingbeingan important seismicevaluationparameter,shouldbe

reflected explicitly in the study, alongwith the total duration. Both these durations can be

estimated using the scaling relations (e.g.Novikova and Trifunac, 1994),which defines the

strongmotiondurationateachfrequencyasafunctionofearthquakemagnitude,sourceto

sitedistanceand site condition.Forgenerationofdesignaccelerograms, the strongmotion

durationmaybetakenastheaveragedurationcorrespondingtothehighestfrequencyband

(1825Hz)and the totalduration canbe takenas theaverageplusone standarddeviation

valuecorrespondingtothelowestfrequencyband(0.100.15Hz)butnotlessthan20seconds.

Localconditionsmayalsoaffecttheexpecteddurationofearthquakeshakingandshouldbe

consideredonacasebycasebasis.

4.6 DevelopmentofAccelerationTimeHistories

The acceleration time histories should preferably be represented by real accelerograms

obtainedforsiteconditionssimilartothosepresentatthedamsiteunderconsideration.Since

thestronggroundmotiondatacurrentlyavailabledonotcoverthewholerangeofpossible

conditions, such records may be supplemented by synthetic motions representing any

earthquakesizeandseismotectonicenvironment.Syntheticearthquakescanbedevelopedby

superpositionmethods6.

It is recommended thatseveralacceleration timehistoriesbeused to represent theground

motionascertaintimehistorieshavelowerenergycontentatsomefrequenciesandtheiruse

mayresultinanunconservativeanalysis.Whendetailedtimehistoryanalysisisnecessaryitis

proposed to use atleast three sets of uncorrelated time histories of horizontal & vertical

motionsandthemaximumresponsetoallthethreesetsbeconsideredfordesignpurposes.

Acceleration time histories should be specified separately for the horizontal and vertical

motions.

4.7 FactorstobeconsideredwhiledecidingthesitespecificTargetResponseSpectrum

Having obtained the target response spectrum from Deterministic as well as Probabilistic

approach,thefollowingconsiderationsmaybehelpfulinadoptingthetargetresponsespectra

inpracticalapplications:

ForMCEcondition:If the spectral amplitudes obtained by the two approaches differ by 25% or less, the

envelopeofbothmaybeadoptedasthedesigntargetspectra.Inothercasesaweighted

average of both the spectra may be adopted as the target spectra, with weights

6Gupta&Joshi (1993).Onsynthesizingresponsespectrumcompatible accelerograms,JournalofEuropeanEarthquakeEngineering,2,2533.


21/34



appropriatelyjustified. Ifthedifference inthespectralamplitudevaluesobtainedbytwo

approacheshappens tobevery large (saymore than100%), then thepossible technical

reasonsforsuchdiscrepanciesshallbeexplainedinthereport.

ForDBEcondition:Intheseismiczones IVandV, ifthespectralamplitudesobtainedbythetwoapproaches

differby25%orless,attheperiodsofinterest,thedesigntargetresponsespectrumshall

beobtainedastheenvelopeofDSHAandPSHADBEestimate(asdescribedinparas4.3.1&

4.3.2).Inothercasesaweightedaverageofboththespectramaybeadoptedasthetarget

spectra,withweightsappropriatelyjustified.However,forseismiczonesII&III,thedesign

target responsespectrum shallbeobtainedas theenvelopeof theDSHAandPSHADBE

estimates.

Theabovecomparisonsaretoberestrictedfornaturalperiodsupto1.0sec

5.0 RECOMMENDATIONSONDESIGNAPPROACH

Thesitespecificseismicstudyreportshouldmentionthedesignapproachtobeadoptedfor

checking the stability of the dam and should also contain recommendations regarding the

permissiblestressesandslidingfactorstobeadopted.Theearthquakeperformanceofgravity

damshastobeevaluatedonthebasisofstresses,slidingfactor,demandcapacityratiosand

the associated cumulative duration. The below mentioned points should be taken in to

accountwhileformulatingrecommendations.

5.1 Seismicanalysisofconcretegravitydamscanstartwithsimplifiedmethodsusingsitespecific

seismiccoefficientforslidingandoverturningstability,andprogresstoamorerefinedanalysis

asneeded. The pseudostaticmethod of analysismaybeused for computationof forces.

Regardingpermissiblestresses,BIScode6512:CriteriafordesignofSolidGravityDamsmaybe

madeuseof.

TheDBElevelofgroundmotionisusedfortheevaluationoftheactualperformanceofgravity

dams. Under DBE, the dam is required to be within linear elastic range with little or no

damage. The spectra and timehistories for DBE level of ground motion can be used to

evaluatethedynamicresponseofgravitydamsbylinearelasticresponsespectrummethodor

thetimehistorymethod.UnderDBEcondition,thedemandcapacityratios(DCR)arerequired

to

beless

than

orequal

to

1.0.

The

DCRisdefined

as

theratio

ofinduced

tensile

stress

to

tensilestrengthoftheconcrete.Forthispurpose,thetensilestrengthorcapacityoftheplain

concrete can be obtained from the uniaxial splitting tension tests or from the static

compressivestrength,fc,usingtherelationduetoRaphel(1984),ft=1.7fc2/3 wherefcisinpsi

orft=0.324fc2/3 wherefcisinMPa,asrecommendedinUSACEManualEM111026051.

UnderMCEcondition,damsshouldnotexperienceacatastrophiclossofthereservoir.Under

therapid loadingofMCEconditions,slidingmayoccuratthedamfoundation interfaceorat

upper elevations at liftjoints.Dams subjected to large lateral forcesproducedby theMCE

groundmotionmaytipandstartrockingandtheresultingdrivingforcemaybecomesolarge

that the structurebreaks contactwith the foundationor cracksall theway through at theupperelevation.


22/34



ThedynamicresponseunderMCEconditionmay firstbeevaluatedusing linearelastictime

historyanalysis.The levelofnonlinear responseorcracking isconsideredacceptable ifDCR

are less than2.0,and limited to15percentof thedam crosssection surfacearea,and the

cumulative duration of stress excursions beyond the tensile strength of the concrete falls

below the performance curve given in Figure 3. DCR of 2.0 corresponds to the apparent

dynamic tensile strength of concrete (Raphel, 1984). The cumulative duration beyond a

certainlevelofDCRisobtainedbymultiplyingthenumberofstressvaluesexceedingthatlevel

bythe timestepused in the timehistoryanalysis. When theseperformanceconditionsare

notmet,anonlineartimehistoryanalysisisrequiredtoestimatethedamagemoreaccurately

underMCEcondition.

Fig.3:Performancecurveforgravitydams

5.2 Incaseofearthendams, the seismic slope stabilityanalysis involves startingwitha simpler

analysis(Pseudostatic)andmovingontoSlidingBlockanalysisandDynamicanalysis,where

complexity of analysis increases in each stage. In pseudostatic slope stability analysis,

earthquake forces are represented by the site specific seismic coefficient. Seismic inertial

forces are estimated by multiplying weight of the potential sliding mass (W) with seismic

coefficientasper IS1893 (1984).Undrainedshearstrengthofthesoil istobeconsidered in

theanalysis.An indexofstability,calledfactorofsafety(FOS) iscomputedfromtheratioof

resistingmomenttodisturbingmoment,forapotentialslidingmass.AFOSof1.0oraboveis

consideredacceptableunderearthquakecondition.Seedssimplifiedapproachmaybeused

todetermine liquefactionpotentialof cohesionless soil strata. The liquefactionpotential is

ascertainedfromindexpropertiesasrecommendedbySeed(2003).

Inslidingblockanalysis,permanentdeformation inanearthendam,duetoanearthquake is

evaluatedbasedonNewmarkconcept.Inthismethod,apotentialslidingmassisassumedasa


23/34



rigidbodyonarigidbaseandcontactbetweenthemasarigidplastic.Theanalysis involves

determination of Yield acceleration (Ky) from slope stability analysis, maximum crest

acceleration (Umax) and average acceleration time history [Kav(t)] of sliding mass and

estimationofpermanentcrestdisplacementbydouble integrationofaccelerationdifference

[Kav(t)Ky]. If the crestdisplacement iswithinpermissible limit (w.r.t FreeBoard)no further

analysis is required. In case the sliding block analysis shows excessive deformation, the

detaileddynamicanalysismaybecarriedout.

Dynamicanalysis iscarriedoutfordams, failureofwhichmay leadtohigh levelofrisk.The

analysisinvolvesdeterminationofcyclicstrengthofsoilfromcyclictriaxialsheartests,induced

shearstressesfromdynamicfiniteelementresponseanalysis(equivalent linearornonlinear)

using site specific earthquake,evaluationof strainpotential in eachelementby comparing

induced shear stresses with shear strength of soils and then determination of overall

deformationofdamfromstrainpotential,whichshouldbewithinpermissiblelimit(w.r.t.Free

Board

provided).

Thedynamicanalysisprocedureisfollowedtodetermineliquefactionpotentialofsoil.Incyclic

triaxialtestsonundisturbedsoilsamples,thecyclicshearstressrequiredtocauseliquefaction

isdetermined.Thestressesthatare likelytobe induced inthegroundaredeterminedfrom

dynamicresponseanalysis.Comparing theinducedstresseswithstressrequired tocause

liquefactionwillindicatesusceptibilityforliquefaction.

6.0 SUBMISSIONOFSTUDYREPORTFORNCSDPAPPROVAL

Thesitespecificstudiesfordeterminationofdesignearthquakeparametersshallhavetobe

carriedoutbyDeterministicaswellasProbabilisticapproach.However,wheretheavailable

data on past seismicity is scanty, and even the data on tectonic features and geological

processes are inadequate to have any meaningful application of probabilistic analysis, the

deterministic analysisonly shallbe carriedoutby recording theproperjustification fornot

adoptingtheprobabilisticapproachforanalysis.

Thereportshouldalsoincludeasection/chaptergivingthefollowinginformation:

Comparison of target response spectra obtained from Deterministic as well asProbabilistic approach forMCE andDBE conditions alongwith final target response

spectra

selected

with

justification

CompatibleaccelerationtimehistoriesforMCE&DBEtargetresponsespectra Computedresponsespectrafordifferentdampingvalues ie2%,3%,5%,10%and15%

atleast

SitespecifichorizontalandverticalSeismiccoefficientsAftercompletionofthesitespecificseismicstudy,thefullstudyreportshouldbecompiledin

asingledossierasperproformagiveninAnnexureC.Thesaidproformashouldalsobefilled

upreflectingthestatusofcompliances(alongwithreasonsfornoncompliances)fordifferent

itemsofthestudy.Thisproforma,dulyfilledandsigned,shouldbefurnishedasachecklistin

thebeginningofthestudyreport.


24/34



Fifteen(15)boundvolumesandonesoftcopyofthestudyreportshouldbesubmittedtothe

NCSDP secretariat (Foundation Engineering & Special Analysis Directorate, Central Water

Commission,712(S),SewaBhawan,R.K.Puram,NewDelhi).Inordertoensureconsideration

of study report in a particular meeting of the NCSDP, the study report should reach the

secretariat at least twomonths aheadof thatmeeting.Only such study reports,which are

foundsatisfactory(intermsofcompliancesoftheguidelines)onpreliminaryinspectionbythe

Secretariat,willbeputuptotheNCSDPforconsiderationandapproval.

7.0 PRESENTATIONOFSTUDYREPORTBEFORENCSDP

Thedateonwhich study report of aparticular projectwill comeupbeforeNCSDPwillbe

intimated by the Secretariat to the project authorities. It will be the responsibility of the

projectauthorities toensurepresenceofexperts/consultantsconnectedwith the studyon

thestipulateddateandtime.TheprojectauthoritieswillmakeaPowerPointpresentationof

thestudyreportbeforeNCSDP,andanswertothequeriesofthemembersoftheCommittee.

The presentation should cover: (i) details of the project; (ii) regional geological & seismo

tectonic setting; (iii) seismichistory; (iv) localgeological setting; (v) studymethodologyand

deviation, if any, from the recommended approach; (vi) evaluated parameters of the site

specificseismicstudy;and(vii)recommendationsondesignapproach.


25/34



AnnexureA

IllustrativeExample: DSHAmethodfordevelopingtargetresponsespectra

Consideringascenarioearthquakeofmagnitude7.5withclosestdistancefromthesitetozoneofenergy releaseas14kmandwith localgeologicalconditions indicatingmassive rock, the

following isestimated fromagroundmotionpredictionequation for5%dampedhorizontal

accelerationspectrum:

PeakGroundAcceleration(atmeanplusonestandarddeviationlevel) =3.934m/s2

7Ps s accel at woperiodsie0.2secand1.0secuedo pectral er ionvaluefort

S 0.2s 8.63m/s2; S 1.0s 5.782m/s2Thusthecontrolperiod(T2)forstartofconstantvelocityr utto0.67sec.ange workso

T . .

x 1s; T .. x 1s 0.67sThecontrolperiodforthebeginn o tacceleration(T1)isobtainedasafractionofingofc nstan

T2as: =0.134secThepseudospectralaccelerationisconsideredtobesameasthepeakgroundaccelerationat

controlperiodT0=0.03s.

Thecontrolperiodforconstantdisplacement(T3)(generallybetween3secto4secforstrongearthquakesinnearfieldconditions) obtained scalingtheconstantvelocitycontrolperiod

(T2)as

is by

=6.25=4.2secThuswehave:

PGA T .934 m s

ST=

8.63 m s

ST

S 3 ;

Thecorrespondingpseudospectral v it eloc ies maybeobtainedas:

S T S Tx T2 0.0188 m/s

S T S Tx T2 0.1868 m/s S T S Tx T2 0.9315 m/sST STx T

2

0.9315 m/s

7Boore-Atknison -Ground motion Prediction equations for the average horizontal component of PGA, PGV and 5%-damped PSA at spectralperiods between 0.01s and 10.0s, Earthquake Spectra, 24(1):99-138,23008


26/34



From these numerical values of pseudospectral velocity and the control periods, the

parametersofthesmoothaccelerationdesignspectrummaybeobtainedas

1 0.534;A 2.194;V 2 x 88;1.4

D 2 x T x STPGA 6.248

TargetResponsespectrumforHorizontalAcceleration(5%dampingLevel)


27/34



77 78 79 80 81 82 83

Longitude, E

27

28

29

30

31

32

33

Latitude,

N

Lineaments Faults Sub-surfacefault

Thrust Gravity fault Suture zone

Gartok (Tibet)

Delhi

Haridwar

Deharadun ProjectSite

Chamoli

Uttarkashi

Nainital

Pithoragarh

Manali

4.0 M < 4.8 4.8 M < 5.6 5.6 M < 6.4 M 7.26.4 M < 7.2

AnnexureB

IllustrativeExample: PSHAmethodfordevelopingtargetresponsespectra

To illustrate the application of the PSHA approach, a typical site shownby solid triangle is

consideredinthe

highly

seismic

Kumaun

Garhwal

Himalayan

region

(Fig.

1).

The

major

tectonic

features in the region canbe divided longitudinally into fivemajor crustal formation zones

identified fromsouth tonorthas (i)outerzoneof the foredeep, (ii) innerzoneof the fore

deepformingtheHimalayanfoothills(iii)LesserHimalayaformedbysuperpositionofaseries

of tectonicnappesandprobably thrustedover the foredeep, (iv) theHighHimalayaand (v)

the IndusTsangpoSuturezone (Dasgupta,2000).The first fourofthesezonesareseparated

fromeachotherby large thrust faults.TheMainFrontalThrust (MFT) runsat theboundary

between theouterand the inner zonesof the foredeep.TheMainBoundaryThrust (MBT)

separatesthenappedfoldedcomplexoftheLesserHimalaya fromthe Himalayan foothills.

A thick strata of crystalline rock comprising the High Himalaya is thrusted over the

metamorphosed deposits of the Lesser Himalaya along the MCT. The belt north of High

Himalayaand

bound

byIndus

Tsangpo

Suture

isknown

asTethys

Himalaya,

which

consists

of

fossiliferroussedimentaryrocks.

Fig.1:Majortectonicfeaturesintheregionoftheprojectsitealongwith

theepicentersofavailablepastearthquakes


28/34



77 78 79 80 81 82 83

Longitude, E

27

28

29

30

31

32

33

La

titude,

N

Project site

Source - 1

Source - 3

Source - 2

Sub-Source - 3

Source - 4

Source -5

Source - 3

4.0 M < 4.8 4.8 M < 5.6 5.6 M < 6.4 M 7.26.4 M < 7.2

InadditiontothemajorstructuraldiscontinuitiesoftheHimalayanregion,thereareanumber

of other faults/lineaments in the region. Within the main Himalayan belt, the high grade

complex of thecentralcrystallines is bound tothenorthandthesouth by MartoliThrust

andMCT,respectively. Asimilarhighgradecomplex,theAlmoracrystallines, isdelimitedon

eithersidebytheNorthAlmoraThrust(NAT)andtheSouthAlmoraThrust(SAT).Furthernorth

oftheMartolithrustisthedextralKarakoramFault,subparalleltotheIndusSutureZone(ISZ).

The belt between the Karakoram Fault and ISZ is occupied by cover rocks affected by the

Himalayanorogeny.Neotectonicactivityhasbeen recordedalong theKarakoramFault, ISZ,

MBTaswellasMFT. AnumberoftransversefaultsalsoexistwithintheHimalayanrangesas

wellastothesouth in the IndoGangeticplanes.Thetransverse featuresarealsoassociated

withvaryinglevelsofseismicity.

ThefirststepinPSHAistoidentifyanddelineatethevariousseismogenicsourcezones(SSZ)in

theregionofabout6lat6longaroundtheprojectsite.Consideringthespatialdistribution

andcorrelationofseismicactivitywiththetectonicfeatures intheregionoftheproject,five

broad seismic sources have been identified, viz. (i) TransHimalayan (TRH) area north of

KarakoramFault, (ii)HimalayanFold (HF)areabetween ISZandKarakoramFault, (iii)Tethys

Himalayan(THH)areabetweenMCTandISZ,(iv)MainHimalayanThrusts(MHT)areaofMCT,

MBT,etc.,and (v)AreaofAravalliFoldBelt (AFB) in the IndoGangeticPlains.These source

zonesareshowndemarcatedbythicksolidlinesinFig.2alongwiththeepicentersofthepast

earthquakes. There is a marked concentration of epicenters along the Kaurik Fault system

(KFS)intheTHHmainsource,whichhasbeenthereforedefinedbyaseparatesubsource.The

othermainsourcesarealsocharacterizedbyvaryingconcentrationsofepicenters,whichhas

beensuitablyaccountedindistributingtheexpectedseismicityoverthecompletesourcezone

toestimatetheoccurrencerate (

,

)ofearthquakesindifferentmagnitudeanddistance

intervals

Fig.2:Possibleseismicsourcezonesintheregionoftheprojectsite


29/34



The second step is to obtain ij RM , for each source zone. For this purpose, first the

GutenbergRichtersearthquake recurrence relationship isdefined for

each source zone, by estimating the constants a and b using maximum likelihood method

(Weichert,1980).TheN(M)isobtainedusingavailablepastearthquakedatainthesourcezone

byhomogenizationof themagnitude (Scordilis,2006),declustering the catalogby removing

fore andaftershocks(GardnerandKnopoff,1974),andaccountingfortheincompletenessof

earthquakes in different magnitude ranges (Stepp, 1973). The recurrence relation is then

suitably modified to consider an upperbound magnitude Mmax (Chinnery and North, 1975).

Typicalrecurrencerelationshipthusobtainedforsourcezone4isshowninFig.3

bMaMN =)(log

Fig.3:Recurrencerelationforsourcezone4

From the recurrence relationship for a source zone with an upper bound magnitude, the

occurrence rateofearthquakeswithina smallmagnitude range ),( jjjj MMMM + aroundcentralmagnitude canbeobtainedasjM

)()()( jjjjj MMNMMNMn +=

Thesenumbersaredistributedappropriatelyusingspatialsmootheningofpastseismicityover

theentire source zone, toget the requirednumber ( )ij RM , withina small sourcetosite

distancerange ),( iiii RRRR + .

In step three, theprobability, ( )ij RMTSAq ,)( ,ofexceedinga responseamplitudeSA(T)atnaturalperiodTduetomagnitude atsourcetositedistance isobtainedbyassuming

the tofollowaGaussianprobabilitydistributionas:jM iR

)(ln TSA

[ ]

=

)(ln 2

)(

)(ln

2

1exp

)(2

1)(

TSA

dxT

TSAx

TTSAF

In this expression )(ln TSA is the least squares estimate and )(T is the associated

standarddeviationof ,whichhavebeenobtained from theempirical attenuation

relationduetoAbrahamsonandSilva(1997),definedat28naturalperiodsbetween0.01sec

and5.0sec.Thecomplementaryof theprobability

)(ln TSA

[ ])(TSAp gives therequiredprobability,ij RMTSAq ,)( .

Fromknowledgeof iR, andthenuMTSAq )( mber ( )in R,M obtainedasaboveforall


30/34



ted

Fig.4:Typicalhazardcurvesatselectednatural riods

TheMCEleveloftargetresponsespectraofhorizontalandverticalcomponentsofmotionwith

Fig.5:The5%dampedtargetspectraforMCEcondition

themainandsubsourc ctionofeqn.(1)is instepfourforallthe28

naturalperiodsforwhichtheselectedattenuationrelationshipisdefined.Fig.4showstypical

hazardcurvesforT=0.02,0.2,1.0and3.0secperiods,where0.02secperiodcorrespondsto

thePGA.

e,thehazardfun compu

pe

damping ratio of 5% are finally obtained by estimating the spectral amplitudes at all the

natural periodswith annualprobabilityof exceedance equal to 0.0004 (returnperiod 2500

years).Theprobabilistic response spectrumof thehorizontalmotion thusobtained for rocktypeofsiteconditionisshowninFig.5.Thecorrespondingmeanplusonestandarddeviation

deterministic response spectrum forMCEmagnitudeof7.5atshortestdistanceof14km to

thefaultruptureplaneisalsoshowninFig.5forthepurposeofcomparison.

0.0001

0.001

A

nnualP

0.01

0.1

robabilityofExceedance

P=0.0004

1E-006 1E-005 0.0001 0.001 0.01 0.1 1

Spectral Acceleration, g

T=0.02s(P

GA)

T=0.2s

T=1.0

sT=3.0s


31/34

AnnexureC

PROFORMAFORSUBMISSIONOFSTUDYREPORTTONCSDP

Thestudyreportshouldbecompiledinasingledossierasperproformagivenbelow.

Theproforma,dulyfilledandsigned,shouldbefurnishedasachecklistinthebeginningofthestudyreport.

Sl

No.

Description Compliance(Yes/No)

w.r.t.Guidelines&

ReasonsforNon

compliance

1 ProjectDetails

(a) NameoftheProject

(b) NameoftheRiveroverwhichtheprojectisproposed

(c) BriefDescriptionoftheProjectComponents

(d) LocationoftheProject:State,District,Longitude&LatitudeandToposheetno.ofeachoftheProject

component (e.g. Dam/Barrage/Power House etc.)for which design seismic

coefficientisrequired.Informationtobegivenintabularformat.

(e) TypeofProject:

Multipurposeor irrigationStorage (area/volumeof reservoir)orRunof the

RiverSchemeorHydroPowerProject(surface/subsurface,InstalledCapacity,

numberofunitsetc.)

(f) Detailsofotherprojectsinthevicinity(within 100km):

Name of project, Type of hydraulic structures, and seismic parameters

(expectedPGAforMCE)forprojectsconstructed/underconstruction.

(g) PresentStatusofInvestigation:DPRsubmitted/approved;Salientcomments/observationsonDPRforground

exploration,relevanttoSeismicdesign;statusonenvironmentclearance;pre

construction/constructionstageetc.

(h) NatureofFoundationMaterial:

Natureoffoundationmaterial(includinggeotechnicalpropertiesofrock/soil

etc.)belowdifferentsegmentsofdamandotherprojectcomponents.

(i) NameandaddressoftheProjectAuthorityandConsultants/ Advisors:

Completepostaladdresswith telephone/fax/email of ProjectAuthority and

Consultants/Advisor engaged by the ProjectAuthorityfor various types of

inputs[geological,

geophysical,

geotechnical,

seismotectonics,

seismic

design

etc]shallbegiven.

2 RegionalGeologicalandSeismoTectonicEvaluation

(ReferSection3.0oftheguidelinesfordetails)

(a) TectonicMap:

(b) Seismotectonicsection:

(c) Interpretationofregionaltectonicmechanismandotherdetails:

(d) Earthquakecatalogue:

(e) Microearthquakeinvestigations:



32/34



3 LocalGeologicSetting


(a) Geologicalmap:

(b) Surface&subsurfaceexploration:

(c) Additionalinputsonsubsurfaceconfigurationofmajorfaults:

4 Evaluationofsitespecificseismicparameters

(a) Methodologyofthestudy:

Theadopted studymethodology,confirming to section4.0of theguidelines,

shouldbebrieflydescribed.Anydeviationfrom the recommendedapproach

shouldbepointedoutwithadequatejustifications.

(b) Evaluatedsitespecificseismicparameters:

The study should furnish the identified MCE (deterministic); recommended

response spectrafor theMCE andDBE conditions; recommended horizontal

andvertical

seismic

coefficients

along

with

computed

natural

period

of

the

dam;estimateddurationofshaking;andacceleration timehistoriesforboth

horizontalandverticalmotions.

5 Recommendationsondesignapproach


6 SubmissionofstudyreportforNCSDPapproval


Date:

Signature&Seal

ofauthorizedrepresentative

ofProjectAuthority


33/34



AnnexureD

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BasicEngineering

Seismology

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Seismology,10,225236.

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GenerationofSpectrumCompatibleAccelograms

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MethodologyofHazardAssessment

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guidelines eq

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