Development of Procedures
for the Rapid Estimation of Ground Shaking
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Task 7: Ground Motion Estimates for
Emergency Response |
Objective
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Develop methodology to automatically
simulate strong ground motion |
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In sparse regional coverage |
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In near-real-time |
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With seamless shakemap product for
areas with & without dense local strong motion instrument coverage |
Task List
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Finalize fault slip models &
inverse methodology |
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Compare predicted to observed ground
motions |
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Investigate site amplification factors |
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Ground motion simulation code
improvements |
Scope of the Problem
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Uneven distribution of strong motion
stations |
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Presently insufficient numbers of
telemetered strong motion stations in northern California |
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Uneven distribution of seismic source
regions |
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Regionally extensive support
infrastructure |
TriNet ShakeMaps for Landers
and Northridge
Data Driven PGA Shakemap in
Deteriorating Coverage
Inverse Methodology
Northridge Fault Slip Models
Slide 9
Slide 10
Predicted PGV (0.1-1.0 Hz)
Efforts to Improve Shakemaps
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Application of site corrections |
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Application of hard rock and soft rock
green’s functions |
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Integration of empirical attenuation
relationships |
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Alternative methods of ground motion
simulation |
PGV Predicted to Observed
Amplitude Ratios Relative to Site Class
Predicted to Observed PGV
Ratios
Empirical Attenuation Model
Shakemap
Implementation Plan
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Automated finite source inversion to
find: |
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Causative fault, fault slip dimension (approximately 15 minutes) |
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Fault slip distribution, rupture
velocity and estimated dislocation rise time (approximately 30 minutes) |
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Preliminary line or course grid results
used to generate a data/model shakemap using the Somerville et al. (1998)
attenuation relationships |
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Approximately 15 minutes |
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Implementation Plan
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Compute conservative shakemap (larger
of the empirical or deterministic calculations) |
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Revised data/conservative-model
shakemap |
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Approximately 45-60 minutes |
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Follow the data/model interpolation and
site adjustment approach of the TriNet ShakeMap (Wald et al., 1999) |
Combined Data/model
Shakemaps (Northridge PGA)
Slide 19
Conclusions
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Code developed for source inversion and
ground motion simulation |
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Empirical site corrections not useful
when applied to simulated ground motions |
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Alternative higher frequency simulation
methods do improve shakemaps but not enough to offset additional
computational cost |
Conclusions
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Site specific green’s functions improve
the maps – application in other areas will require calibration |
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Directivity capable attenuation
relationship improves shakemaps in several ways |
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Very rapid preliminary maps |
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Seamless base model for different
levels of approximation |
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Base model for development of source
specific conservative model |
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Reasonable estimates of peak and
spectral values of ground motions |
Recommendations
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Develop model based site corrections
using numerical methods |
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Extend the Somerville et al. (1997)
attenuation relationship to include PGV and PGD |