Numerical modelling of the three-dimensional stress field in southwestern Japan
Numerical modelling of the three-dimensional stress field in southwestern Japan
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DOI：
10.1016/0040-1951(82)90162-7
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发表时间：
1982-04
期刊：
影响因子：
2.9
通讯作者：
M. Hashimoto
中科院分区：
文献类型：
--
作者：
M. Hashimoto
从地震的震源机制和震源分布推断（Shiono，1977）认为日本西南部的应力场具有复杂的特征;沿南海海槽沿着浅部为NW-SE向挤压，内陆地壳为E-W或ESE-WNW向挤压，从中部南部到四国西北部地区，在地壳下深处平行于菲律宾海板块前缘的延伸，为了研究这些复杂应力状态的可能来源，本文采用三维有限元方法模拟了菲律宾海板块俯冲过程中的形态，考虑了以下三种可能的力：1. (1)由于俯冲板块与周围地幔的密度差异，产生了负浮力。(2)菲律宾海板块运动产生的西北挤压力。(3)由于太平洋板块的运动而产生的向西的挤压力。对于这些力的不同大小和不同弹性模量的各种组合，计算了一些选定地点的应力，结果表明，观测到的伸展应力方向与俯冲菲律宾海前缘平行板块的负浮力可能主要是造成的。北西向挤压力对日本西南部复杂应力场的形成可能不起重要作用。内陆地区所观测到的东西向挤压应力场似乎主要是太平洋板块西移的结果。本文的结果表明，如果俯冲菲律宾海板块之上存在一个薄的低速过渡层，它将对纪伊半岛和四国岛附近的低角度逆冲断裂机制产生明显的影响，陆壳和俯冲板块中的剪应力值估计为几百巴量级，虽然计算的剪应力受俯冲板块的形状和外力的影响很大，但有趣的是，应力分布似乎与壳下地震的地震活动性以及沿板块边界沿着的大逆冲地震的破裂过程有某种关系。
It has been inferred from the focal mechanism of earthquakes and their hypocenter distribution (Shiono, 1977) that the stress field in southwestern Japan indicates complicated features; a NW-SE compression at shallow depths along the Nankai trough, an E-W or ESE-WNW compression in the inland crust, an extension parallel to the leading edge of the Philippine Sea plate at subcrustal depths in the region from the southern Chubu to northwestern Shikoku, and a down-dip tension beneath the Kyushu island.In order to investigate possible sources of these complex features of the stress state, a three-dimensional finite element method is employed to model the configuration of the subducting Philippine Sea plate, taking into consideration the following three possible types of forces:1.(1) A negative buoyancy due to the density contrast between the subducting plate and the surrounding mantle.2.(2) A northwestward compressive force generated by the movement of the Philippine Sea plate.3.(3) A westward compressive force due to the movement of the Pacific plate.For various combinations of different magnitudes of these forces, and of different elastic moduli, the stresses at a number of selected sites are calculated, and their directions are compared with those inferred from the focal mechanism and other geophysical information.It is found that the observed extensional stresses parallel to the leading edge of the subducting Philippine Sea plate may be caused mainly by the negative buoyancy. The northwestward compressive force may not play an important role in generating the complex stress field in southwestern Japan. The observed E-W compressional stress field prevailing in the inland region appears to result mainly from the westward-moving Pacific plate. The present results suggest that if a thin low-velocity transitional layer exists just above the subducting Philippine Sea plate, it could give appreciable effects on the mechanism of low-angled thrust faulting off the Kii peninsula and the Shikoku island.The magnitude of the shear stress in the continental crust and in the subducting plate is estimated to be of the order of several hundred bars, although the calculated shear stresses are considerably affected by the configuration of the subducting plate and also by the applied forces.It is interesting that the stress distribution appears to have some relations to seismicity of subcrustal earthquakes, and to the rupture process of large thrust earthquakes along the plate boundary.