Rapid determination of global moment-tensor solutions

In an effort to improve data services, the National Earthquake Information Center has begun a program, in cooperation with the Incorporated Research Institutions for Seismology Data Management Center (IRIS DMC), to produce rapid estimates of the seismic moment tensor for most earthquakes with a body-wave magnitude of 5.8 or greater. Although this program is still undergoing testing and fine-tuning, an estimate of the moment tensor can usually be produced within 20 minutes of the arrival of the broadband P-waveform data from the IRIS DMC. Although the speed with which this data can be obtained varies, in many cases a solution can be obtained within two hours of the earthquake. These solutions do not vary significantly from the final solutions determined using the entire network. Because of the manner in which the data and the synthetic seismograms are aligned, the method is insensitive to the effects of timing errors, epicentral mislocation, and lateral heterogeneity in earth structure. This procedure was implemented in May 1993; the results from that month are presented here.