[S-SS15] 地震発生の物理・断層のレオロジー

[SSS15-12] 2016年熊本地震震源域における応力場のモデル化（３）

*松本 聡¹、光岡 郁穂²、飯尾 能久³、酒井 慎一⁴、2016年熊本地震 合同地震観測グループ (1.九州大学大学院理学研究院附属地震火山観測研究センター、2.九州大学大学院理学府、3.京都大学防災研究所、4.東京大学地震研究所)

キーワード：2016年熊本地震、応力場、時空間変化

The 2016 Kumamoto earthquake sequence (maximum magnitude 7.3) occurred in the Beppu-Shimabara area, Kyushu, Japan. The sequence was located at one of the highest background seismicity region in the Kyushu Island. Pre-state of stress in this area revealed spatial heterogeneous feature and the largest earthquake fault slipped to follow the maximum shear stress direction on the fault under the heterogeneous stress. In addition, behavior of the faults having complex geometry created stress heterogeneity although average stress level should decline due to the earthquake occurrence. In this study, we attempt to model of the stress field around the 2016 Kumamoto earthquake from seismic moment tensor data before and after the occurrence. Strong spatial stress heterogeneity detected in this region as pointed out by previous studies. Spatial regional stress pattern did not change after the earthquake occurrence except area just around the co-seismic fault. The change in deviatoric stress tensor associated with the co-seismic fault slip have been detected around fault. Considering co-seismic stress change, we estimated the differential stress less than few tens MPa. In addition, the stress concentration at the faults before the earthquake was expected about half magnitude of the released stress. These result suggests that stress condition in the hypocentral area of the sequence is complex and unstable due to low stress and strong heterogeneity.