AUTOMATED NEAR-REALTIME CMT INVERSION

The Earthquake Research Institute (ERI) of the University of Tokyo has completely automated the process of determining source mechanisms of earthquakes using waveform data. The solutions are automatically distributed using the Internet without being checked. The process is initiated by receipt of e-mail giving the origin time and location of an earthquake. To determine the source mechanism, we apply the Harvard centroid moment tenser (CMT) inversion method to long-period body wave data (the portion of the seismogram from the first arrival to the initial surface wave). The method has been successfully applied since October 1993 to all of the major earthquakes in the world for which we received event e-mail. 108 of the 242 CMT solutions in 1994 were determined within 6 hours of the event, with an average delay of 3.8 hours. For local events (e.g., events around Japan), it is also possible to determine CMT solutions within 30 minutes from the occurrence of the earthquakes, using an efficient dialup data retrieval system operated by ERI.