Source process of the 21 April, 1997 Santa Cruz Island earthquake (M(w) 7.8)

Abstract

We apply an Empirical Green's function method to recordings of teleseismic body waves from the April 21, 1997 Santa Cruz Island earthquake. The far-field moment rate functions reveal that rupture occurred on a shallow dipping fault plane (dip 17°). The main rupture consists of 6 large subevents and covers a total area of about 5000 km2. While the hypocenter is fixed at 33 km depth, the main slip is located above 20 km depth within the accretionary wedge. The source duration is about 70 sec and the average rupture velocity is found to be 1.9 km/sec. This event caused a local tsunami and although it is not possible to determine whether it was caused by tectonic faulting or submarine shaking the fact that most of the moment release occurred at shallow depths is consistent with either of these possibilities, and points to the utility of the procedure outlined here in possible rapid characterization of tsunami potential.