An Evaluation of the SCSN Moment Tensor Solutions: Robustness of the Mw Magnitude Scale, Style of Faulting, and Automation of the Method

Abstract We have generated moment tensor solutions and moment magnitudes (Mw) for 1700 earthquakes of local magnitude (ML) 3. 0 that occurred from Sep-tember 1999 to November 2005 in southern California. The method is running as an automated real-time component of the Southern California Seismic Network (SCSN), with solutions available within 12 min of event nucleation. For local events, the method can reliably obtain good-quality solutions for Mw with ML 3. 5, and for the moment tensor for events with ML 4. 0. The method uses the 1D Time-Domain INVerse Code (TDMTINVC) software package (Dreger, 2003). The Green’s func-tions have been predetermined for various velocity profiles in southern California, which are used in the inversion of observed three-component broadband waveforms (10–100 sec), using data from at least four stations. Moment tensor solutions have an assigned quality factor dependent on the number of stations in the inversion, and the goodness of fit between synthetic and observed data. If a minimum quality factor is attained, the ML or Mw is 5. 0 or greater, and if the event is in the southern California reporting regions, the Mw will be the official SCSN/CISN magnitude.