Structural, Mineralogical, and Geochemical Characterization of the Chelungpu Thrust Fault, TaiwanTerrestrial, Atmospheric and Oceanic Sciences
PublisherChinese Geoscience Union
AbstractThe Chelungpu fault, Taiwan, produced a northward propagating ruptureon 21 September 1999 resulting in a Mw 7.6 earthquake with a ~90 kmlong N-S trending fault scarp. The mineralogic and physical character ofthe fault-related rocks within the Chelungpu fault zone, as measured at9 sites along 70 km of the 1999 rupture trace, changes significantly alongstrike and with depth. The northern section of the Chelungpu fault has a10 - 30 m-wide primary damage zone that is characterized by increasedfracture density and alteration, but little microstructural damage to within1 m from the main fault. The southern section of the Chelungpu fault has a25 - 70 m wide primary damage zone that is characterized by increasedfracture density and alteration, the presence of intensely sheared rock, andnumerous secondary faults and gouge zones as far as 240 m from the mainfault. The complexity of the damage zone, geochemistry, and clay mineralogyof the southern fault zone may reflect its relative maturity (~1 Ma)compared to the northern fault zone (~46 - 100 Ka). The major down-dipmineralogic variation is a transition from a significant amount of smectitein exhumed fault cores to little or no smectite in the fault core at sampleddepths of 200 to 1000 m. This transition may be influenced by weatheringprocesses at the surface, however co-seismic fluid flow may have a role inillite-smectite reactions. The composition of clays has important seismologicimplications as clays play a role in fault weakening.
Citation InformationIssacs, A. J., Evans, J. P., Song, S. R., and Kolesar, P. T., 2007, Structural, mineralogical, and geochemical characterization of the Chelungpu thrust fault, Taiwan, TAO Sciences, v. 18, p. 183-221.