Study on slip property of the slow earthquake source region in the transition zone on the subducting plate interface

重新评价了菲律宾海板块俯冲界面上发生的非火山性震颤目录，阐明了新的震颤迁移模式和时空演化规律。地震活动模式显示沿倾斜方向的深度依赖性。这表明板界面上的摩擦性能随深度的变化而变化。为了揭示地震活动模式的深度依赖关系，我们在日本西南地区最活跃的震源区之一四国西部部署了80台地震仪，两年的地震仪沿板块界面倾斜方向变化。我们对局地和远震地震记录的分析表明，地震带下方的海洋地壳具有低v和高Vp/Vs的特征。与震颤带不活跃部分相对应的俯冲板块界面的平坦几何形状可能表明，板块的几何不规则性控制着缓慢的地震活动。

The catalog of the non-volcanic tremor occurring on the interface of the subducting Philippine Sea plate is reevaluated and new pattern of tremor migration and spatiotemporal evolution have been clarified. The tremor activity pattern indicates depth dependency along the dip direction. This suggests that the frictional property on the plate interface changes with depth. In order to reveal the depth dependency of tremor activity pattern, we deployed 80 seismometers for two years in western Shikoku which is one of most active tremor source areas in southwest Japan, changes along the dip direction of the plate interface. Our analysis of local and teleseismic seismograms revealed that the oceanic crust just beneath the tremor zone is characterized by low-V and high Vp/Vs. The flat geometry of the subducting plate interface corresponding to the inactive part of tremor zone may suggest that the geometrical irregularities of the plate control the slow earthquake activity.