日本地球惑星科学連合2018年大会

講演情報

[JJ] Eveningポスター発表

セッション記号 S (固体地球科学) » S-SS 地震学

[S-SS15] 地震発生の物理・断層のレオロジー

2018年5月21日(月) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:向吉 秀樹(島根大学大学院総合理工学研究科地球資源環境学領域)、谷川 亘(国立研究開発法人海洋研究開発機構高知コア研究所)、松澤 孝紀(国立研究開発法人 防災科学技術研究所、共同)、吉田 圭佑(東北大学理学研究科附属地震噴火予知研究観測センター)

[SSS15-P18] Stress drops of moderate-sized earthquakes on the Pacific Plate off the Tohoku region, Japan.

*段 美佟1山田 卓司1 (1.茨城大学)

An earthquake rupture occurs at a point where the shear stress reaches the shear strength. As the difference between the initial and residual stress levels of an earthquake is defined as a stress drop, the vales of stress drops can be used to infer the frictional properties on the fault plane.

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.