Report

Strong Ground Motion Prediction Using Virtual Earthquakes

Science  24 Jan 2014:
Vol. 343, Issue 6169, pp. 399-403
DOI: 10.1126/science.1245678

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Abstract

Sedimentary basins increase the damaging effects of earthquakes by trapping and amplifying seismic waves. Simulations of seismic wave propagation in sedimentary basins capture this effect; however, there exists no method to validate these results for earthquakes that have not yet occurred. We present a new approach for ground motion prediction that uses the ambient seismic field. We apply our method to a suite of magnitude 7 scenario earthquakes on the southern San Andreas fault and compare our ground motion predictions with simulations. Both methods find strong amplification and coupling of source and structure effects, but they predict substantially different shaking patterns across the Los Angeles Basin. The virtual earthquake approach provides a new approach for predicting long-period strong ground motion.

Noise in Motion

A large earthquake along the southern San Andreas Fault has the potential to cause serious damage to the city of Los Angeles, USA. Earthquake simulations in this region, which lies in a sedimentary basin capable of amplifying shaking, predict strong ground motion but they lack validation with observational data. Denolle et al. (p. 399) developed an independent method to predict ground motion using virtual earthquakes and information gleaned from background seismic noise. This ambient seismic field—generated by sources such as the oceans and atmosphere—produces differences in ground motion in the Los Angeles Basin compared to simulations, but suggests that locally shaking could on average be 3 times larger than the surrounding areas.

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