Co-seismic frictional melting along an out-of-sequence thrust in the Shimanto accretionary complex. Implications on the tsunamigenic potential of splay faults in modern subduction zones
Co-seismic frictional melting along an out-of-sequence thrust in the Shimanto accretionary complex. Implications on the tsunamigenic potential of splay faults in modern subduction zones
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DOI：
10.1016/j.epsl.2006.02.039
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发表时间：
2006-05
影响因子：
5.3
通讯作者：
H. Mukoyoshi;A. Sakaguchi;K. Otsuki;T. Hirono;W. Soh
中科院分区：
文献类型：
--
作者：
H. Mukoyoshi;A. Sakaguchi;K. Otsuki;T. Hirono;W. Soh
序列外逆冲断层在俯冲带增生棱柱体增厚、弧前盆地形成和海啸形成中起着重要作用。通过对地质构造和古地质构造的详细研究，在日本西南部的四万十增生杂岩中发现了一个古地震构造带。这OST由一个可映射的雁行断层系统在增生过程的后期阶段发展。根据热分析估算的累积位移量为2.5 - 8.5km，形成深度为2.5 - 5.5km，表明断裂活动性较强，具有左旋走滑性质，大位移量分布在多条小错距的小断裂之间。雁列断层系统中的大多数断层记录了重复的脆性破坏，一个断层保存了假玄武玻璃，这是一种指示地震断层的断层岩。这是第一次在增生棱柱体中沿沿着OST发现假玄武玻璃。在同一个狭窄的剪切带（每个只有几毫米厚）反复破裂表明，OST作为主要的剪切局部化区的增生棱柱体。浅估计的地层深度和随之而来的低正应力也支持这一假设的弱耦合沿着该断裂带。这些发现是在雅阁活动在增生棱柱体的浅部与破裂传播从深孕震区。这OST显示高活动性和重复断裂的加积棱柱体的浅部，可比的海底海啸OST在现在的南海海槽。
Out-of-sequence thrusts (OST) play an important role in the thickening of accretionary prisms, formation of forearc basins, and tsunami generation in subduction zones. By detailed investigations of geological and paleogeothermal structures, an ancient seismogenic OST is identified in the Shimanto accretionary complex, southwest Japan. This OST consists of a mappable en echelon fault system developed at a late stage of the accretionary process. The estimated accumulated displacement of 2.5–8.5km and formation depth of 2.5–5.5km, based on a thermal analysis, indicates much higher fault activities sense of slip with a sinistral slip, and the large displacement was distributed among multiple small faults each with a small offset. Most of the faults in the en echelon fault system recorded repeated brittle failure, and one fault preserves pseudotachylyte, a fault rock indicative of seismic faulting. This is the first report of pseudotachylyte along an OST in an accretionary prism. Repeated fracturing in the same narrow shear zones (each only a few millimeters thick) suggests the OSTs perform as major shear localized zone in the accretionary prism. Shallow estimated formation depth and consequent low normal stress also support the hypothesis by a weak coupling along this fault zone. These findings are in accord with a thrust activity in the shallow portion of the accretionary prism being associated with rupture propagation from the deep seismogenic region. This OST showed high activity and repeated faulting in the shallow portion of the accretionary prism, comparable to that of the submarine tsunamigenic OST in the present Nankai trough.