SOURCE PROCESS OF THE 21 APRIL, 1997 SANTA-CRUZ ISLAND EARTHQUAKE (M-W 7.8)

We apply an Empirical Green's function method to recordings of telesei smic body waves from the April 21, 1997 Santa Cruz Island earthquake. The far-field moment rate functions reveal that rupture occured on a s hallow dipping fault plane (dip 17 degrees). The main rupture consists of 6 large subevents and covers a total area of about 5000 km(2) Whil e the hypocenter is fixed at 33 km depth, the main slip is located abo ve 20 km depth within the accretionary wedge. The source duration is a bout 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 sha king the fact that most of the moment release occured at shallow depth s is consistent with either of these possibilities, and points to the utility of the procedure outlined here in possible rapid characterizat ion of tsunami potential.