Rayleigh-wave multi-pathing along the west coast of North America

Abstract

We have created a movie of surface ground motions for the November 3, 2002, Denali fault earthquake based upon spectral-element simulations using crustal model CRUST2.0, mantle model S20RTS, topography and bathymetry model ETOPO5, and a finite-fault slip model. The movie features two anomalous wave packets that travel along the west coast of the North American plate following off-great-circle paths. These wave packets are Rayleigh waves with dominant periods around 20 sec, which are also found in seismograms recorded by the Southern California Seismic Network. One of these packets is the direct surface wave, whose group arrival-time changes laterally as dictated by the shape of the Oregon coast. The other packet is a surface wave reflected by a lateral interface underneath the Rocky Mountains. A linear reflector parallel to the Canadian coast offsetting it by a few hundred kilometers can explain its arrival time, but the offsetting distance derived from the synthetic seismograms puts the reflector 350 km northeast of the result obtained from the data, indicating a need to update the crustal and mantle models in this area.