[S13-P] Poster

[S13-P-10] Early rupture process of the 2016 Kumamoto earthquake inferred from source imaging

^○Takamasa Usami, Masanao Komatsu, Hiroshi Takenaka (Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan)

The 2016 Kumamoto earthquake (Mj 7.3) occurred in Kumamoto prefecture, Japan, on 16 April 2016 (JST). The source region includes the Futagawa fault and northern part of the Hinagu fault. In this study, we investigate the early rupture process during 2.5 seconds after the origin time by source imaging technique (Takenaka et al., 2009, EPS). We use P-wave portion on vertical components of waveform records at 40 seismic stations from the seismic networks of JMA, NIED and Kyushu University. We assume three fault segments: first one (segment 0) is the plane of strike N100E and dip 71 degrees passing the hypocenter by JMA focal mechanism; second one (segment 1) is the plane of strike N205E and dip 72 degrees for northern part of the Hinagu fault estimated by GSI; third one (segment 2) is the plane of strike N235E and dip 60 degrees for the Futagawa fault inferred by GSI. In the result of source imaging on these segments, we found several characteristic slip region. On segment 0, the rupture initiated and propagated. Then, at after 0.5 seconds from the origin time, relatively larger slip appeared on the intersection line with segment 1, and the rupture transferred to segment 1. On segment 1, we found two strong slip regions: at southwest side of the segment after 2.0 seconds from the initial break; at near the shallower part of the intersection line with segment 2 after 2.3 seconds from the origin time. The latter slip shows that the rupture did not overcome the intersection line with segment 2. This feature suggests that the shallower part of the junction with segment 2 worked as a barrier at the stage of initial rupture and the rupture might have transfer to segment 2 from deeper part of the junction at the later stage.