4:15 PM - 4:30 PM
[SSS02-21] Spatiotemporal changes in the b-value along the plate interface before and after the 2011 Tohoku earthquake constrained by ocean bottom seismic network: Post-Tohoku
Keywords:b-value, the 2011 Tohoku earthquake, OBS data, back projection
Therefore, in this study, we analyze seismicity including small earthquakes along the plate interface using data from ocean bottom seismometers (OBSs) obtained during extensive seafloor aftershock observations [Shinohara et al., 2011, 2012] and recurrent OBS observations off Miyagi by Tohoku University. In order to automatically detect and locate interplate earthquakes, we applied a back projection method based on semblance analysis [Nakatani et al., 2015, GRL] to the data. In order to inspect validity of our method, we conducted three kinds of tests: synthetic tests, focal mechanism tests, and focal depth tests. We confirmed the validity of our method to evaluate seismicity along the plate interface. Also, we appropriately corrected event magnitudes determined by OBS records, which are, in general, overestimated due to large amplifications caused by seafloor sediments, by comparing with those listed in the JMA (Japan Meteorological Agency) catalog. Finally, we obtained an original earthquake catalog which shows an improvement in completeness of magnitude for interplate earthquakes. The resulted distribution of seismicity for the first three months after the main shock shows mutually complementary relationship between the active area of interplate aftershocks and the large coseismic slip zone. We also observe spatial variation of the b-value during the same observation period.
Acknowledgements: This work was supported by the MEXT of Japan, under KAKENHI and contract researches.