Ground Motion Prediction Using the Ambient Seismic Field

Speaker: Greg Beroza
The waves generated by faulting represent the primary threat posed by most large earthquakes. The effect of complex geological structure, such as sedimentary basins, on earthquake ground motion is a source of particular concern. The usual approach to predicting such effects is to image the Earth’s crustal structure, and then to propagate waves through that structure using numerical modeling techniques. At long periods it is possible to extract reliable phase and amplitude response for the elastodynamic Green’s function from the ambient seismic field using deconvolution. These Green’s functions can be used to improve elastic and anelastic structural models, which will improve ground motion prediction. We demonstrate the accuracy of the approach by predicting complex ground motion for a moderate (Mw = 4.6) earthquake in southern California as recorded in the Los Angeles Basin. This experiment suggests a novel approach to seismic hazard analysis in which ground motion from hypothetical future earthquakes may be simulated directly, without the need for modeling the detailed heterogeneity of the Earth’s crust as an intermediate step.