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

主要研究结果如下：1.在澳大利亚中部的Woodroffe逆冲断层和中国中部Diabe-Tonbei地区的超高压变质杂岩中，发现了多代体积巨大的碎裂岩、糜棱岩以及与碎裂岩和糜棱岩有关的假玄武玻璃体。这些断层岩的共存表明，假玄武玻璃体代表了大量的大地震和伴随地震滑动在这两个断层上的地震活动的延长期。假玄武玻璃的形成时间和分布表明，地震在脆性为主的孕震带底部成核，并通过脆-韧性转变向下传播，进入地壳韧性为主的机制。2.在Itoigawa-Shizuoka构造线活动断层系统的Simotsuburai断层中发现了破碎成因的假玄武玻璃。1999年台湾集集7.6级地震的地表破裂主要受先存的陈龙埔断裂带控制，该断裂带分布在宽达60 m的区域内，尽管主要的同震滑动位于小于0.3 cm的狭窄区域内。对陈龙铺断裂带剪切带和断层岩的构造分析表明，陈龙铺断裂带自更新世形成以来，一直以逆冲断层的形式活动，具有明显的左旋走滑分量。4. 2001年11月14日，藏北昆仑山中段发生了昆仑山中段8.1级地震。研究表明：（1）沿先存昆仑断裂带的同震破裂距离为沿着420 km;（2）同震地表破裂以走滑断裂为主，左旋位移达16.3 m ;（3）沿同震破裂带发育广泛的同震莫尔迹构造，其分布范围沿着。

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.