A nonlinear method to estimate source parameters, amplitude, and travel times of teleseismic body waves

We present a nonlinear waveform inversion method to determine source parameters under point-source approximation (depth, source time function, centroid moment tensor, and seismic moment) and also travel times and amplitudes of body waves from teleseismic records. We demonstrate that our source time function estimates significantly improve correlation between observed and synthetics broadband seismograms. The scaling of source dimensions with seismic moment is similar for deep and shallow events in the Japanese subduction area for moment magnitudes between 6.1 and 7.5. We compare event depths and moment tensors obtained with our method to those reported by different institutions for a set of Japanese earthquakes. This comparison reveals that our method gives hypocentral depths closer to those obtained with regional arrays than other teleseismic methods. The seismic moment is properly recovered, but data weighting strongly influences the moment tensor solution. Focal mechanisms are biased by high-frequency body-wave amplitude variations due to crustal structure below the stations and by errors on the instrument responses. Body-wave differential travel times are improved compared with phase-picking measurements. The high-quality travel times will be exploited to obtain more precise event locations and higher resolution tomographic models.