Seismotectonics and Identification of Potential Seismic Source Zones in Taiwan

We use the focal mechanisms of 97 small-to-moderate-sized earthquakes(2.7≤M(subscript L)≤5.7)given by a comprehensive focal mechanism study fromRau et al.(1996)to determine the style of faulting and the state of stress inthe active Taiwan orogen.The nature of faulting of the 97 minor earthquakesis characterized by a mixture of reverse,normal,and strike-slipfaults.Thirty of the 97 events studied are reverse faulting events;24 ofthem occurred under the Western Foothills and the Central Range,mostlywithin a depth range of 10-32 km and a dip angle range of 30-70°.Thesteeply dipping nodal planes and their deep focal depths demonstrate thatthe reverse faulting is not confined above a detachment surface,but occursin the crystalline basement at high angles.Normal faulting events are observedunder the northern Central Range in both upper and lower crustallevels and under the Western Foothills in the upper crustal level.The shallownormal faulting under the northern Central Range is probably associatedwith the uparching of the core of the orogen,causing the vertical stressto be greater under the orogen than under the lowlands.The cause of thedeep normal faulting under the Central Range is enigmatic.In the WesternFoothills,under the flank of the Central Range,the shallow normalfaulting may also be a result of the uparching of the core of the orogen,while the deep reverse faulting is caused by the horizontal compression.The stress tensors estimated are heterogeneous throughout the entire Taiwanregion,with the exception of south-central Taiwan where a nearly homogeneousstress field is observed.Although the spreads of the 95% confidenceregion for σ1 and σ3 are relatively large for most stress models,theyare consistent with the direction of the plate motion of the Philippine Seaplate relative to the Eurasian plate.

並列關鍵字

Seismotectonics ； Seismic Potential Source Zone ； Seismic Hazards

國際替代計量

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