Teleseismic inversion for the second-degree moments of earthquake space-time distributions

Abstract

Determining detailed descriptions of the space–time distribution of an earthquake's rupture using only teleseismic data is often a difficult and non unique process. However, a description of an earthquake that goes beyond a point source is often needed for many seismotectonic problems. We have developed a method that inverts measurements of the shifts in traveltime and amplitude of various seismic phases at global stations for the second degree polynomial moments of an event's space–time distribution. Our values for the second moments of the 1995 Mw 8.0 Jalisco, Mexico, thrust event correspond to a characteristic rupture length of 121±10 km along strike, a characteristic rupture width of 76±11 km downdip, a characteristic duration of 29±2 s, and a direction of rupture propagation along the strike of the subduction zone to the NW. For the 1995 Mw 7.2 Gulf of Aqaba earthquake, our estimates of the second moments correspond to a characteristic rupture length of 53±2 km, a characteristic duration of 12±1 s, and rupture propagation to the NE along the strike of the Dead Sea Transform. Our estimates of the first and second moments agree well with values from local seismic and geodetic networks. For both the Jalisco and Aqaba events, we are able to resolve the fault plane ambiguity associated with the events' moment tensors using our estimates of the second spatial moment.