TY - JOUR
T1 - Subsurface structure, physical properties, fault-zone characteristics and stress state in scientific drill holes of Taiwan Chelungpu Fault Drilling Project
AU - Hung, Jih Hao
AU - Ma, Kuo Fong
AU - Wang, Chien Yin
AU - Ito, Hisao
AU - Lin, Weiren
AU - Yeh, En Chao
N1 - Funding Information:
We are grateful to all the participants of TCDP including project principal investigators, international collaborators from USGS, Stanford University, JAMSTEC, and universities and research institutes in Japan, and field assistants and students from NCU and NTU. Funding of the TCDP is primarily from National Science Council (NSC), R.O.C. We thank the International Continental Scientific Drilling Program (ICDP) for providing partial fund and technical consult. Comments and suggestions from David Wiltschko and an anonymous reviewer help us greatly improve this manuscript. This research was supported by the Taiwan Earthquake Research Center (TEC) funded through National Science Council (NSC) with grant number NSC93-2119-M-008-019 and NSC94-2119-M-008-009 JH. The TEC contribution number for this article is 00021.
PY - 2009/3/10
Y1 - 2009/3/10
N2 - Continuous cores and a suit of geophysical measurements were collected in two scientific drill holes to understand physical mechanisms involved in the large displacements during the 1999 Chi-Chi earthquake. Physical properties obtained from wire-line logs including P- and S-wave sonic velocity, gamma ray, electrical resistivity, density and temperature, are primarily dependent on parameters such as lithology, depth and fault zones. The average dip of bedding, identified from both cores and FMI (or FMS) logs, is about 30° towards SE. Nevertheless, local azimuthal variations and increasing or decreasing bedding dips appear across fault zones. A prominent increase of structural dip to 60°-80° below 1856 m could be due to deformation associated with propagation of the Sanyi fault. A total of 12 fault zones identified in hole-A are located in the Plio-Pleistocene Cholan Formation, Pliocene Chinshui Shale and Miocene Kueichulin Formation. The shallowest fault zone occurs at 1111 m depth (FZ1111). It is a 1 m gouge zone including 12 cm of thick indurate black material. We interpreted this zone as the slip zone during Chi-Chi earthquake. FZ1111 is characterized by: 1) bedding-parallel thrust fault with 30-degree dip; 2) the lowest resistivity; 3) low density, Vp and Vs, 4) high Vp/Vs ratio and Poisson's ratio; 5) low energy and velocity anisotropy, and low permeability within the homogeneous 1 m gouge zone; 6) increasing gas (CO2 and CH4) emissions, and 7) appearance of smectite within the primary slip zone. In situ stresses at the drill site were inferred from leak-off tests, borehole breakouts and drilling-induced tensile fractures from borehole FMS/FMI logs, and shear seismic wave anisotropy from DSI logs. The dominant fast shear-wave polarization direction is in good agreement with regional maximum horizontal stress axis, particularly within the strongly anisotropic Kueichulin Formation. A conjugate set of secondary directions are parallel to microcrack orientations. A drastic change of orientation of fast shear-wave polarization across the Sanyi thrust fault at the depth of 1712 m reflects the change of stratigraphy, physical properties and structural geometry.
AB - Continuous cores and a suit of geophysical measurements were collected in two scientific drill holes to understand physical mechanisms involved in the large displacements during the 1999 Chi-Chi earthquake. Physical properties obtained from wire-line logs including P- and S-wave sonic velocity, gamma ray, electrical resistivity, density and temperature, are primarily dependent on parameters such as lithology, depth and fault zones. The average dip of bedding, identified from both cores and FMI (or FMS) logs, is about 30° towards SE. Nevertheless, local azimuthal variations and increasing or decreasing bedding dips appear across fault zones. A prominent increase of structural dip to 60°-80° below 1856 m could be due to deformation associated with propagation of the Sanyi fault. A total of 12 fault zones identified in hole-A are located in the Plio-Pleistocene Cholan Formation, Pliocene Chinshui Shale and Miocene Kueichulin Formation. The shallowest fault zone occurs at 1111 m depth (FZ1111). It is a 1 m gouge zone including 12 cm of thick indurate black material. We interpreted this zone as the slip zone during Chi-Chi earthquake. FZ1111 is characterized by: 1) bedding-parallel thrust fault with 30-degree dip; 2) the lowest resistivity; 3) low density, Vp and Vs, 4) high Vp/Vs ratio and Poisson's ratio; 5) low energy and velocity anisotropy, and low permeability within the homogeneous 1 m gouge zone; 6) increasing gas (CO2 and CH4) emissions, and 7) appearance of smectite within the primary slip zone. In situ stresses at the drill site were inferred from leak-off tests, borehole breakouts and drilling-induced tensile fractures from borehole FMS/FMI logs, and shear seismic wave anisotropy from DSI logs. The dominant fast shear-wave polarization direction is in good agreement with regional maximum horizontal stress axis, particularly within the strongly anisotropic Kueichulin Formation. A conjugate set of secondary directions are parallel to microcrack orientations. A drastic change of orientation of fast shear-wave polarization across the Sanyi thrust fault at the depth of 1712 m reflects the change of stratigraphy, physical properties and structural geometry.
KW - Borehole breakouts
KW - Chi-Chi earthquake
KW - Fault-zone properties
KW - S-wave anisotropy
KW - Taiwan Chelungpu Fault Drilling Project
UR - http://www.scopus.com/inward/record.url?scp=60649107827&partnerID=8YFLogxK
U2 - 10.1016/j.tecto.2007.11.014
DO - 10.1016/j.tecto.2007.11.014
M3 - 期刊論文
AN - SCOPUS:60649107827
SN - 0040-1951
VL - 466
SP - 307
EP - 321
JO - Tectonophysics
JF - Tectonophysics
IS - 3-4
ER -