Development of Procedures for the Rapid Estimation of Ground Shaking

	Task 7: Ground Motion Estimates for Emergency Response

Objective

	Develop methodology to automatically simulate strong ground motion
		In sparse regional coverage
		In near-real-time
		With seamless shakemap product for areas with & without dense local strong motion instrument coverage

Task List

	Finalize fault slip models & inverse methodology
	Compare predicted to observed ground motions
	Investigate site amplification factors
	Ground motion simulation code improvements

Scope of the Problem

	Uneven distribution of strong motion stations
	Presently insufficient numbers of telemetered strong motion stations in northern California
	Uneven distribution of seismic source regions
	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

	Application of site corrections
	Application of hard rock and soft rock green’s functions
	Integration of empirical attenuation relationships
	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

	Automated finite source inversion to find:
		Causative fault, fault slip dimension (approximately 15 minutes)
		Fault slip distribution, rupture velocity and estimated dislocation rise time (approximately 30 minutes)
	Preliminary line or course grid results used to generate a data/model shakemap using the Somerville et al. (1998) attenuation relationships
		Approximately 15 minutes

Implementation Plan

	Compute conservative shakemap (larger of the empirical or deterministic calculations)
	Revised data/conservative-model shakemap
		Approximately 45-60 minutes
	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

	Code developed for source inversion and ground motion simulation
	Empirical site corrections not useful when applied to simulated ground motions
	Alternative higher frequency simulation methods do improve shakemaps but not enough to offset additional computational cost

Conclusions

	Site specific green’s functions improve the maps – application in other areas will require calibration
	Directivity capable attenuation relationship improves shakemaps in several ways
		Very rapid preliminary maps
		Seamless base model for different levels of approximation
		Base model for development of source specific conservative model
		Reasonable estimates of peak and spectral values of ground motions

Recommendations

	Develop model based site corrections using numerical methods
	Extend the Somerville et al. (1997) attenuation relationship to include PGV and PGD