Why do earthquakes occur? -to clarify the true role of crustal fluids-

为了弄清地壳流体的真实作用，我们研究了长野县西部地区震源分布与三维速度和电阻率结构的关系。我们发现，地震发生在被大范围低速和低阻率区包围的高速区中的小尺度低速带上。认为在大范围低速低阻地区，滞弹性变形发生在相对较低的孔压下，而在大范围低速低阻地区，断层上产生高速滑动，地震在高孔压条件下发生。

To clarify the true role of crustal fluids, we investigated the relationship between the hypocentral distribution and the three dimensional velocity and resistivity structures in the Western Nagano Prefecture region. We found that earthquakes occur along small-scale low velocity zones in high velocity regions surrounded by large-scale low velocity and low resistivity regions. It is thought that in the large-scale low velocity and low resistivity regions, anelastic deformation occurs under a relatively low pore pressure, but that in the large-scale low velocity and low resistivity regions, high speed slips are generated on faults and earthquakes occur under a high pore pressure.