Comparison of Recorded and Simulated Ground Motions

Presented by:Emel Seyhan, PhD StudentUniversity of California, Los Angeles

Collaborators:Lisa M. Star, PhD Candidate, University of California, Los AngelesRobert W. Graves, PhD, USGSJonathan P. Stewart, PhD, PE, University of California, Los Angeles

OutlineMotivationHybrid Simulation ProcedureValidation Analysis & Results

Distance scalingStandard deviation

Calibration of Hybrid Simulation ProcedureDistance attenuationStandard deviation

Conclusions

Motivation

Broadband motions for response history analysis

Some (M, R) ranges poorly sampled by recordings

Motions needed with specific attributes, e.g.Basin effectNear fault effects

Motivation

Broadband motions for response history analysis

Some (M, R) ranges poorly sampled by recordings

Motions needed with specific attributes, e.g.Basin effectNear fault effects

Simulations hold potential to provide useful ground motions for engineering application in these situations

ShakeOut Scenario Description

Moment magnitude 7.8 earthquake 150 yr return period (last events 1857 & 1680) Evaluated for three different possible hypocenters

Hughes Lake

San Gorgonio Pass

Bombay Beach

Puente Hills ScenarioDirectly under down

town Los Angeles7.15 Mw EarthquakeBuried reverse fault

Simulation Procedure

Hybrid proceduref<1 Hz: physics based

Physics-based

Simulation Procedure

Hybrid proceduref<1 Hz: physics basedf>1 Hz: stochastic

Stochastic

Reference: Graves et al, 2004

Simulation Procedure

Hybrid proceduref<1 Hz: physics basedf>1 Hz: stochastic

Reference: Graves et al, 2004

Simulation ProcedureHybrid procedureSource function

Kinematically prescribed source model

Slip distributionRupture velocity

ShakeOut, Mw 7.8

Hybrid procedureSource functionSemi-empirical site term (fn of Vs30)

Simulation Procedure

Distance Attenuation

Calibration AnalysisApproachCalculate residuals

4 GMPEs: AS, BA, CB, CYRandom effect analysis: Separate event term (hi) from within-event residual (ei,j)

Distance-scaling evaluated from (ei,j)

, ,i j i i jR h e

i a sim,i a GMPE,iR (T)=ln(S (T)) -ln(S (T))

Calibration Analysis

recording "j" of eqk "i"

i

Genereal Model

ji

General Model

ei,j = Ri,j - hi

Intra-event Residuals

Intra-event Standard Deviation

s too low for T < 1.0 sLarge transition at T=1.0 s

s=stdev(e)

Calibration of Hybrid Simulation ProcedureFocus on high frequency stochastic modelControlling parameters

Source parameters: Stress drop, slip function, rise time, rupture velocity

Path parameters: Distance, crustal velocity & damping (Q)Site parameters: Near surface crustal velocity, shallow site

term (Vs30)Parameter selected for remove distance attenuation biasProcedure to increase intra-event standard deviation

ScopeDistance attenuation calibration

Strike slip fault M5, 6.5, 7.25 and 8Distributed arrays

M5 M6.5 M7.25 M8

Slip modelsFor M5, 6.5, 7.25 and 8Random slips

M5

M6.5

M7.25

M8

Various levels of crustal damping, QLow Qo (a=25)Mid Qo (a=41)High Qo (a=57)

Q (f) = Qo*fn

(n = 0.6)

Qo = a + b*Vs

(b = 34)

ShakeOut

Verification of Hybrid Trends Using Stochastic Part OnlyUsing same level of Q

(Low Qo) Original ShakeOutThis study (M8) similar

trend with previous work esp. beyond about 10 km

Removing Distance Attenuation Bias

Comparing different level of Q (M7.25) Using low Qo

Using high Qo

Removing Distance Attenuation Bias

Residuals for different level of Q (M7.25) Using low Qo

Using high Qo

Removing Distance Attenuation Bias

Fit semi-log line to residuals of average ground motions

For different level of Q Using low Qo

Using high Qo

Repeat for all M, GMPEs, IMs

Y = c*ln(X) + d

Removing Distance Attenuation Bias

Slope of residuals of average ground motionsScatter based on all

gmpesUsing low Qo

Using high Qo

PGA

Removing Distance Attenuation Bias

Slope of residuals of average responses

Using low Qo

Using high Qo

Intra-event scatter calibrationIncreasing intra-event

standard deviationRandomized velocity Randomized Fourier

AmplitudeRandomized Q

ApproachModify parameters e.g.

Velocity profile

Intra-event scatter calibration

Rand CaseNonRand CaseBA08

ApproachRandomization of

Fourier AmplitudeAdding variation

Intra-event scatter calibration

ApproachRandomization of

Fourier AmplitudeAdding variation

Intra-event scatter calibration

Rand CaseNonRand CaseBA08

Concluding RemarksCalibrated simulation procedures needed for

engineering practiceValidation process reveals:

Faster distance attenuation at shorter periodsLow intra-event standard deviation T<1s

Cont’dCalibration process reveals:

Possible to get slower distance attenuation by using higher Q

Randomization of Fourier Spectrum gives better results than randomization of velocity

More? Implementation fully hybrid simulation with revised

Q and Vs

Thank you