Structural, Mineralogical, and Geochemical Characterization of the Chelungpu Thrust Fault, Taiwan

Document Type

Article

Journal/Book Title/Conference

Terrestrial, Atmospheric and Oceanic Sciences

Volume

18

Issue

2

Publisher

Chinese Geoscience Union

Publication Date

2007

First Page

183

Last Page

221

Abstract

The Chelungpu fault, Taiwan, produced a northward propagating rupture
on 21 September 1999 resulting in a Mw 7.6 earthquake with a ~90 km
long N-S trending fault scarp. The mineralogic and physical character of
the fault-related rocks within the Chelungpu fault zone, as measured at
9 sites along 70 km of the 1999 rupture trace, changes significantly along
strike and with depth. The northern section of the Chelungpu fault has a
10 - 30 m-wide primary damage zone that is characterized by increased
fracture density and alteration, but little microstructural damage to within
1 m from the main fault. The southern section of the Chelungpu fault has a
25 - 70 m wide primary damage zone that is characterized by increased
fracture density and alteration, the presence of intensely sheared rock, and
numerous secondary faults and gouge zones as far as 240 m from the main
fault. The complexity of the damage zone, geochemistry, and clay mineralogy
of the southern fault zone may reflect its relative maturity (~1 Ma)
compared to the northern fault zone (~46 - 100 Ka). The major down-dip
mineralogic variation is a transition from a significant amount of smectite
in exhumed fault cores to little or no smectite in the fault core at sampled
depths of 200 to 1000 m. This transition may be influenced by weathering
processes at the surface, however co-seismic fluid flow may have a role in
illite-smectite reactions. The composition of clays has important seismologic
implications as clays play a role in fault weakening.

Comments

Originally published by the Chinese Geoscience Union. Publisher's PDF available through remote link.

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