For understanding the physical condition of earthquake generation, we estimated the deviatoric stress fields and fault planes of the large earthquakes in the hypocentral area of the 2016 Kumamoto earthquake sequence, central Kyushu, Japan. We analyzed precise hypocenters and their focal mechanism tensors from 1993 to 2017 and found the complex fault planes of the largest foreshock and the mainshock during the sequence. The faults of large earthquakes could not be detected from the preceding high seismic activity in the area to the mainshock. The analyses of the deviatoric stress tensors obtained from pre‐ and post‐sequence seismic moment tensor data revealed the temporal change in the deviatoric stress field at the vicinity of the hypocenters of the largest foreshock and the mainshock. Because of this temporal change, we found that the stress level of the deviatoric stress field in this region is the same level as the co‐seismic stress change caused by the two large earthquakes. We attempted to estimate the differential stress at the region using a new method, which can be applied to the heterogeneous stress fields. The average value of the estimated differential stresses in the region was 15.4 ± 10 MPa. The rotation of the principal stress axes and the low differential stress are important information to understand the physical processes of the earthquake generation and the state of the crustal stress.

中文翻译：

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2016年熊本地震序列次震区周围应力状态的时空变化

为了了解地震发生的物理条件，我们估算了日本九州中部2016年熊本地震序列次震区的大地震的偏应力场和断层。我们分析了1993年至2017年的精确震源及其震源机制张量，发现了该序列中最大的前震和主震的复杂断层。大地震的断层不能从先前到主震区的高地震活动中检测到。从前后地震矩张量数据获得的偏应力张量的分析揭示了最大前震和主震震源附近偏应力场的时间变化。由于时间的变化，我们发现该区域偏应力场的应力水平与两次大地震引起的同震应力变化的水平相同。我们尝试使用一种新方法来估计该区域的差异应力，该方法可以应用于非均质应力场。该区域的估计差应力的平均值为15.4±10 MPa。主应力轴的旋转和低微分应力是了解地震发生的物理过程和地壳应力状态的重要信息。可以应用于非均质应力场。该区域的估计差应力的平均值为15.4±10 MPa。主应力轴的旋转和低微分应力是了解地震发生的物理过程和地壳应力状态的重要信息。可以应用于非均质应力场。该区域的估计差应力的平均值为15.4±10 MPa。主应力轴的旋转和低微分应力是了解地震发生的物理过程和地壳应力状态的重要信息。