An Observation of Rupture Pulses of the 20 September 1999 Chi-Chi, Taiwan, Earthquake from Near-Field Seismograms

Chen, Kou-Cheng; Huang, Bor-Shouh; Wang, Jeen-Hwa; Huang, Win‐Gee; Chang, Tzu-Heng; Hwang, Robert R.; Chiu, Hsiang Chih; Tsai, Chih-Hsin

doi:10.1785/0120000716

Cited by 37 publications

(19 citation statements)

References 12 publications

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“…The Chi‐Chi earthquake (21 September 1999, Mw = 7.6) produced a surface rupture of 80 km, and up to 10 m offset on the northern part of the Chelungpu thrust fault [ Kao and Chen , 2000; Chen et al , 2001a; Yu et al , 2001]. It was recorded by the very dense Taiwan Strong Motion and GPS Networks allowing models of spatial slip distribution [ Ma et al , 2001], determination of rupture velocity [ Chen et al , 2001b], coseismic and postseismic deformation [ Pathier et al , 2003; Yu et al , 2003]. The Taiwan Chelungpu Fault Drilling Project (TCDP) started in 2002 and drilled two vertical boreholes 40 m apart (2000.3 m deep Hole A and 1352.6 m deep Hole B), about 2 km east of the surface rupture, near the town of DaKeng (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Microscale anatomy of the 1999 Chi‐Chi earthquake fault zone

Boullier

Yeh

Boutareaud

et al. 2009

Geochem Geophys Geosyst

116

130

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[1] Two TCDP boreholes A and B were drilled in the northern part of the Chelungpu thrust fault where the Chi-Chi earthquake (21 September 1999, Mw 7.6) showed large displacement, low ground acceleration, and high slip velocity. In this paper, we describe the microstructures of the Chi-Chi Principal Slip Zone (PSZ) within black gouges localized at 1111 m depth in Hole A and at 1136 m depth in Hole B. In the FZA1111 the PSZ is a 2 cm-thick isotropic clay-rich gouge which contains aggregates formed by central clasts coated by clay cortex (clay-clast aggregates (CCAs)) and fragments of older gouges segregated in the top third of the PSZ. In FZB1136 the PSZ is 3 mm thick and is characterized by a foliated gouge displaying an alternation of clay-rich and clast-rich layers. The presence of CCAs, plucked underlying gouge fragments, gouge injections, and the occurrence of reverse grain size segregation of large clasts in the FZA1111 isotropic gouge suggest that the gouge was fluidized as a result of frictional heating and thermal pressurization. The foliated gouge in FZB1136 may be one locus of strain localization and related heat production. Small calcite veins present above the isotropic FZA1111 PSZ gouge and, characterized by an increasing strain with increasing distance away from the PSZ, are attributed to coseismic fluid escape from the pressurized gouge. The observed microstructures are interpreted in view of their seismic implications for the Chi-Chi earthquake in terms of slip weakening mechanisms by thermal pressurization, gouge fluidization, coseismic fluid distribution, and postseismic slip. Above the PSZ, several layers of compacted gouges containing deformed CCAs and gouge fragments correspond to several PSZ of past earthquakes similar to the Chi-Chi earthquake and display a fault-parallel cleavage resulting from a low strain rate pressure solution deformation mechanism that may be correlated to the interseismic periods.

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Section: Introductionmentioning

confidence: 99%

Microscale anatomy of the 1999 Chi‐Chi earthquake fault zone

Boullier

Yeh

Boutareaud

et al. 2009

Geochem Geophys Geosyst

116

130

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“…The hypocenter was located at 23.853°N and 120.816°E with a focal depth of 8 km [ Ma et al , 1999] (Figure 1). The earthquake initiated from the hypocenter in southern Chelungpu fault and ruptured both updip and laterally northward [ Chen et al , 2001; Kikuchi et al , 2000; Ma et al , 2000]. The faulting produced surface ruptures about 100 km long along the Chelungpu fault with largest net slip of up to 11.5 m in the north [ Lee et al , 2003].…”

Section: Introductionmentioning

confidence: 99%

Nondestructive continuous physical property measurements of core samples recovered from hole B, Taiwan Chelungpu‐Fault Drilling Project

Hirono¹,

Yeh²,

Lin³

et al. 2007

J. Geophys. Res.

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The Taiwan Chelungpu‐Fault Drilling Project was undertaken in 2002 to investigate the faulting mechanism of the 1999 Mw 7.6 Taiwan Chi‐Chi earthquake. Hole B penetrated the Chelungpu fault, and core samples were recovered from between 948.42‐ and 1352.60‐m depth. Three major zones, designated FZB1136 (fault zone at 1136‐m depth in hole B), FZB1194, and FZB1243, were recognized in the core samples as active fault zones within the Chelungpu fault. Nondestructive continuous physical property measurements, conducted on all core samples, revealed that the three major fault zones were characterized by low gamma ray attenuation (GRA) densities and high magnetic susceptibilities. Extensive fracturing and cracks within the fault zones and/or loss of atoms with high atomic number, but not a measurement artifact, might have caused the low GRA densities, whereas the high magnetic susceptibility values might have resulted from the formation of magnetic minerals from paramagnetic minerals by frictional heating. Minor fault zones were characterized by low GRA densities and no change in magnetic susceptibility, and the latter may indicate that these minor zones experienced relatively low frictional heating. Magnetic susceptibility in a fault zone may be key to the determination that frictional heating occurred during an earthquake on the fault.

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“…The earthquake was located at 23.853°N and 120.816°E with a focal depth of 8 km and a thrust faulting focal mechanism with a strike of 5°, a dip of 34° and a rake of 65° [ Chang et al , 2000]. The earthquake initiated from the hypocenter in southern Chelungpu fault and ruptured both upward and laterally northward [ Chen et al , 2001; Kikuchi et al , 2000; Ma et al , 2000]. The thrust faulting produced surface ruptures about 100 km long along the Chelungpu fault with the largest displacement of 5 and 9 meters in the vertical and horizontal directions, respectively [ CGS , 1999].…”

Section: Introductionmentioning

confidence: 99%

Conjugate thrust faulting associated with the 1999 Chi‐Chi, Taiwan, earthquake sequence

Chen

Huang

Wang

et al. 2002

Geophysical Research Letters

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[1] The geometrical structure of the responsible faults of the 20 September 1999 Chi-Chi, Taiwan, earthquake (M L = 7.3, M w = 7.6) and its aftershocks can be clearly depicted by well-located hypocenters and focal mechanisms of large aftershocks. The mainshock and two large aftershocks with M L = 6.8 were characterized by thrust faulting along a N-S striking fault plane dipping to the east. The underground structure of the Chelungpu fault, which is probably merging with the decollement beneath the Western Foothills, can be clearly associated with the seismicity pattern and the focal mechanisms of the three largest events. A group of deeper aftershocks including two moderate events (M L = 6.3 and 6.0, respectively) were located to the southeast of the mainshock along a fault plane dipping steeply to the west down to a depth of about 30 km. Our results suggest that the spatial pattern of the aftershocks in the southern part of the source area can be interpreted by a conjugate-fault system. This conjugate-fault system is comprised of the gently east-dipping Chelungpu fault and a steeply west-dipping deeper fault zone.

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An Observation of Rupture Pulses of the 20 September 1999 Chi-Chi, Taiwan, Earthquake from Near-Field Seismograms

Cited by 37 publications

References 12 publications

Microscale anatomy of the 1999 Chi‐Chi earthquake fault zone

Microscale anatomy of the 1999 Chi‐Chi earthquake fault zone

Nondestructive continuous physical property measurements of core samples recovered from hole B, Taiwan Chelungpu‐Fault Drilling Project

Conjugate thrust faulting associated with the 1999 Chi‐Chi, Taiwan, earthquake sequence

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