Repeated mechanism of large earthquake-formation mechanism of large scale pseudotachylytes

本课题取得的主要成果如下：1。在澳大利亚中部的Woodroffe逆冲构造和中国中部Diabe-Tonbei地区的超高压变质杂岩中发现了多代体积庞大的碎裂岩、糜棱岩、碎裂岩和与糜棱岩相关的伪岩。这些断层岩的共存表明，这些伪断层岩代表了这两条断层在长时间的地震活动中发生了大量的大地震和伴随的地震滑动。伪水杨酸盐的时间和分布表明，地震在脆性为主的发震带底部成核，并通过脆性-韧性过渡向下传播到地壳的韧性为主区。在日本中部伊藤川-静冈县构造线活动断裂系统的simo郊区断裂中发现了挤压起源的伪岩。1999年台湾赤赤7.6 Mw地震的地表破裂主要受陈伦堡断裂带控制，陈伦堡断裂带分布在宽达60 m的宽带内，而同震滑动主要位于小于0.3 cm的窄带内。3 .对陈伦堡断裂剪切带和断岩的构造分析表明，陈伦堡断裂形成于更新世以来，为逆冲断层，具有明显的左旋滑成分。2001年11月14日，西藏北部昆仑中部山区发生里氏8.1级地震。研究表明：1)同震破裂沿昆仑断裂带存在约420 km；2)同震地表破裂以走滑断裂为主，左移较大，位移达16.3 m；3)沿同震破裂带发育广泛的同震摩尔道构造。

Main results obtained in this project are as follows.1.Multiple generations of voluminous cataclaiste, mylonite, cataclasite-and mylonite-related pseudotachylytes are found in the Woodroffe thrust, central Australia and ultrahigh pressure metamorphic complex in Diabe-Tonbei region, central China. The co-existence of these fault rocks indicates that the pseudotachylytes represent a large number of large earthquakes and accompanying seismic slip over an extended period of seismicity on these two faults. The timing and distribution of pseudotachylyte shows that the earthquakes nucleated at the base of the brittle-dominated seismogenic zone and propagated down through the brittle-ductile transition into the ductile-dominated regime of the crust.2.Crushing-originated pseudotachylytes are found from the Simotsuburai fault of the Itoigawa-Shizuoka tectonic Line active fault system, central Japan.3.The surface rupture of the 1999 Mw 7.6 Chi-Chi (Taiwan) warthquake was controlled primary by the pre-existing Chenlungpu fault zone, which is distributed in a wide zone of upto 60 m, although the main co-seismic slip is located in a narrow zone of <0.3 cm. The structural analyses of the shear zone and fault rocks found in the Chenlungpu fault show that the Chenlungpu fault has slipped as a thrust fault with a significant left-lateral slip component since its formation in the Pleistocene.4.The magnitude (Ms) 8.1 Central Kunlun earthquake occurred on 14 Novermber 2001, in the central Kunlun mountain area, north Tibet. Our studies reveal 1) that the co-seismic rupturing over a distance of 〜420 km along the pre-existing Kunlun fault zone ; 2) the co-seismic surface rupture was dominated by strike-slip faulting with a large left-lateral displacement up to 16.3 m ; 3) extensive co-seismic mole track structures are developed along the co-seismic rupture zone.