Characteristics of the Lithology, Fault-related Rocks and Fault Zone Structures in the TCDP Hole-A

Probing a fault zone of recently major activity at depth to study the physical, mechanical and chemical properties is the one of main purposes of the Taiwan Chelungpu-fault Drilling Project (TCDP). We have finished drilling the hole-A which it has the cuttings from 0 to 430 m and cores from 430 to 2003.67 m deep in the end of 2004. Stratigraphically, from surface to 1029 m deep is the Pliocene to Pleistocene Cholan Formation which is dominantly composed of sandstone and sandstone-siltstone alternation with weak to heavy bioturbations. The Pliocene Chinshui Shale occurs from 1029 to 1303 m deep and predominantly consists of siltstone with weak bioturbation. From 1303 to 1712 m deep is the late Miocene to early Pliocene Kueichulin Formation and is dominantly composed of massive sandstone with minor siltstone. Below the 1712 m deep, the Formation is back to the younger Cholan Formation with mollusca-rich thick layered shale and heavy bioturbated sandstone. Four kinds of fault rocks can be identified in the cores. They are the fault breccia, gouge, foliated and non-foliated cataclasites and pseudotachylyte. At least six major fault zones can be found in the cores: FZ1111, FZ1153, FZ1222, FZ1580, FZ1712 and FZ1818. In those fault zones, the FZ1111 may be correlative to the surface rupture of Chi-Chi earthquake,1999, while the FZ1712 may be the Sanyi fault.