Feasibility of Real-Time Broadband Waveform Inversion for Simultaneous Moment Tensor and Centroid Location Determination

by Fumiko Tajima, Charles Mégnin, Douglas S. Dreger, and Barbara Romanowicz

Abstract

We present a feasibility study for an automated system to simultaneously determine centroid source location and seismic moment tensor (MT) for regional earthquakes. This system uses continuous real-time waveforms in a time window that is continuously shifted forward with a short time interval (∼20 sec) from a sparse network of broadband seismic instruments, and unlike the current standard method, it performs inversion without prior knowledge of the location and origin time information. We tested 68 earthquakes with M_L ≥4.2 that occurred in northern and central California between 1993 and 1999 and that have well-calibrated solutions obtained by an established procedure of MT determination. The solutions determined by the new system are compared with the well-calibrated solutions for performance appraisal. Results show that onshore earthquakes with M_w ≥4.5 can be detected and adequately characterized in terms of MT and approximate centroid location. The threshold value of variance reduction to detect an event is about 70%. In contrast, events that occurred off the Mendocino coast are not as reliably constrained, reflecting the unmodeled complexity of the transitional structure from ocean to the continent using the current 1D model as well as the gap in azimuthal coverage. Significant improvement of the computational efficiency is expected if the system is fully configured on a powerful PC with multiple CPUs of approximately 1 Gbyte memory and the monitoring of event location and MT determination over the grid can be updated within the time frame of shifting the time window (∼20 sec).

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