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

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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.