Otsubo Makoto, Miyakawa Ayumu, Katayama Ikuo, Okazaki Keishi
Geological Survey of Japan, AIST, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, 305-8567, Japan.
Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima, 739-8526, Japan.
Sci Rep. 2019 Jan 30;9(1):994. doi: 10.1038/s41598-018-38142-w.
Nonvolcanic, deep low-frequency tremors and slow-slip events occur simultaneously in the transition zone from locked to continuously creeping fault in the down-dip portion of the Nankai Trough subduction zone, southwestern Japan. The occurrence of these slow earthquakes is discontinuous along the trench and attributed to the effect of high pore pressures at the plate boundary. Here, we show that spatial variations in intraslab stress may control fluid migration from the subducted Philippine Sea slab to the plate boundary. The triaxial normal faulting stress, detected by stress tensor inversion using focal mechanisms in the slab, controls anisotropically permeability that trends NNW-SSE subhorizontally from the subducted Philippine Sea slab to the plate boundary. The inhomogeneous permeability controlled by spatial stress heterogeneities in the subducted Philippine Sea slab controls the intraslab fluid pathway. This hypothesis is consistent with the spatial heterogeneity of slow earthquakes and He/He ratio distributions.
在日本西南部南海海槽俯冲带的下倾部分，从锁定断层到持续蠕动断层的过渡带中，非火山性的深部低频震颤和慢滑事件同时发生。这些慢地震的发生沿海沟是不连续的，并且归因于板块边界处高孔隙压力的影响。在这里，我们表明板内应力的空间变化可能控制流体从俯冲的菲律宾海板块向板块边界的迁移。通过使用板块中的震源机制进行应力张量反演检测到的三轴正断层应力，各向异性地控制着渗透率，该渗透率从俯冲的菲律宾海板块到板块边界呈北北西 - 南南东方向近乎水平地延伸。由俯冲的菲律宾海板块中的空间应力非均匀性控制的非均匀渗透率控制着板内流体通道。这一假设与慢地震的空间非均匀性以及氦/氦比值分布是一致的。
