Calibrating the International Monitoring System for Moment Tensor Solutions

We are implementing seismic moment tensor software routinely used at the Berkeley Seismological Laboratory (BSL) on the test bed at the Center for Monitoring Research (CMR) to provide additional information for the discrimination of nuclear explosions from naturally occurring earthquakes, particularly for moderate magnitude events. For selected events which occurred in 1999 we demonstrate the application of the method to data from the very sparse network consisting of primary stations of the International Monitoring System (IMS), as well as the improvement obtained using data from auxiliary stations. We investigate the lower magnitude limits of the method by applying it to aftershocks, in addition to the selected mainshocks. For events in the Mediterranean region, for example, we can achieve good solutions down to moment magnitude 4.8. For events in the Lop Nor region, we compare results for earthquakes and a few of the most recent nuclear explosions.