[SSS15-P18] Stress drops of moderate-sized earthquakes on the Pacific Plate off the Tohoku region, Japan.
In this study, we analyzed stress drops of 2456 moderate-sized earthquakes with magnitudes of 4.2 to 5.0 on the Pacific Plate off the Tohoku region, Japan, from June 2002 to December 2016. We used 100-sps velocity waveforms observed at NIED Hi-net stations as well as Japanese universities and Japan Meteorological Agency. We assumed that the source spectra can be described by the omega-squared model (Boatwright, 1978) and investigated the corner frequency of the earthquakes by deconvolving the spectra by collocated smaller earthquakes with M3.5.
Figure 1 shows the spatial pattern of obtained stress drops. Earthquakes close to the hypocenter of the 2011 Tohoku earthquake indicate higher stress drops. In addition, our results are similar to Uchide et al. (2014), who analyzed the spatial pattern of stress drop before the 2011 earthquake. This would suggest that the frictional properties are stable in time, consistent with Yamada et al. (2017).
We are going to report the relation to the focal depth and temporal characteristics at the presentation.