Change of the source mechanism of the main shock of the 2004 off the Kii peninsula earthquakes inferred from long period body wave data

Waveform inversion of long period body wave data was performed to determine the temporal distribution of moment release of the main shock of the 2004 off the Kii peninsula earthquakes. Our result suggests that the source mechanism varied during the rupture, with the first 20 sec dominated by the strike slip component, while a thrust mechanism was predominant between 30–40 sec. The employed dataset has enough resolving power to detect temporal change on such a time scale, and thus our results suggest that this earthquake is a compound event consisting of the two different source mechanisms.