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

重新评价了俯冲菲律宾海板块界面上发生的非火山地震类型，阐明了地震迁移和时空演化的新格局。地震活动模式指示了沿倾角方向的深度依赖性。这表明板界面上的摩擦特性随深度的变化而变化。为了揭示地震活动模式的深度依赖性，我们在四国西部部署了80个地震仪两年，四国西部是日本西南部最活跃的震源区之一，沿板块界面的倾角方向变化。我们对本地和远震地震图的分析表明，震动区下方的洋壳具有低V和高Vp/V的特征。俯冲板块界面对应于震动带非活动部分的平坦几何形状可能表明，板块的几何不规则性控制了慢震活动。

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.