Fluid accumulation beneath the detachment fault in the Central Range of Taiwan

概要

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Hypocenter of the Chi-Chi earthquake is located on the detachment fault distributed approximately 10 km of depth, near the boundary between continental basement and overlying continental shelf sediments. Exhumed section of the basement rocks underwent greenschist facies (350-450℃) metamorphism. Overlying Eocene-Miocene sediments (termed as Slate Belt) also underwent sub-greenschist facies (<350℃) metamorphism. We found an outcrop-scale duplex structure exposed in the Slate Belt, suggesting an outcrop of the detachment fault. The outcrop consists of alternation of sandstone and slate layers. It is notable that pegmatitic, V-shaped quartz veins in the sandstone concentrate beneath the detachment fault, suggesting cracks filled with fluid by hydrofaulting. At this time, overlying slate layers play a major role as an impermeable cap-rock. If the stored fluid beneath the detachment was expelled to the pre-existing link thrust, cracks in the fault zone would propagate and facilitate the rupture process of the earthquake.
日本地質学会の論文
2005-02-15