[S01-3] Open session III

[S01-3-03] The 30 May 2015 Bonin Deep Earthquake and the 660-km Discontinuity Around its Source Region

^○Keiko Kuge (Department of Geophysics, Kyoto University, Kyoto, Japan)

The 30 May 2015 Bonin deep earthquake occurred near the bottom of the mantle transition zone (depth 664 km, Mw 7.8; USGS), and its seismic waves traversed the mantle to many broadband stations in a distance range that may be affected by the 660-km discontinuity in and around the source region. Our results from finite-fault inversion with the P and SH waveforms and observations of aftershock waveforms suggest that a significant, subhorizontal 660-km discontinuity could not be located below the source region. Seismic waves from the Bonin earthquake were recorded by a number of broadband stations in a wide range of distance around the world. Along with the data collected by IRIS DMC, we examined broadband data of F-net in Japan. Since high-frequency waves, which could be associated with the descending Pacific slab, were observed in eastern Japan, we used the data only from western Japan, which range from 7 to 16 degrees in distance. Changing the depth of the 660-km discontinuity in iasp91, we obtained spatiotemporal distribution of slip on a finite fault by the multiple-time-window method (Kuge, 2003; Kuge et al., 2010). Relatively small amounts of slip were estimated above the assumed 660-km discontinuity. When the 660-km discontinuity was assumed below the earthquake source, the waveform fit became worse, compared with the cases above. These results are consistent with the observation of a simple pulse for P waves over western Japan from an aftershock.