Subsurface Structure, Physical Properties, and Fault Zone Characteristics in the Scientific Drill Holes of Taiwan Chelungpu-Fault Drilling Project

Abstract

: 1) a bedding-parallel thrust fault with a 30-degree dip; 2) the lowest resistivity; 3) low density, V p and V s ; 4) high V p /V s ratio and Poisson's ratio; 5) low energy and velocity anisotropy, and low permeability or fluid mobility within the homogeneous gouge zone; 6) increasing gas (CO 2 and CH 4 ) emissions; and 7) being rich in smectite within the primary slip zone.Formation physical properties hold consistent relationships with either depth or lithology. Anisotropy of shear-wave velocity shows that the dominant fast shear polarization direction is in good agreement with an overall azimuth of the maximum horizontal stress axis, particularly within the strong anisotropic Kueichulin Formation. A drastic change in orientation of fast shear polarization across the Sanyi thrust fault at a depth of 1710 m reflects changes in stratigraphy, physical properties and structural geometry.

Core Description and Characteristics of Fault Zones from Hole-A of the Taiwan Chelungpu-Fault Drilling Project

“…(b) Cross section through the drill site illustrates the relation between formations and major fault zones (after Hung et al 2007). …”

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

“…At the TCDP drillsite, a fault zone at ~1111 m depth is interpreted as the 1999 slip surface (for example, Hung and Ma 2006;Hung et al 2007;Sone et al 2005Sone et al , 2007). This fault zone contains <1 m of light gray, wet, massive clay that grades into ~10 -15 cm of foliated fault gouge.…”

Architecture and Hydraulic Relevance of Brittle Fault Zones in the Metamorphic Basement of the Pannonian Basin

“…These suggest that the intensely deformed parts of the fault zones (cataclasites and fault gouges) can be characterized by low densities and resistivities and that further elevated natural gamma activity and compensated neutron porosity values mark the fault core, which is consistent with the observations of Hung et al (2007) and Jeppson et al (2010). The density and resistivity logs imply intensive fracturing, fragmentation and communition, while the natural gamma and neutron porosity values indicate strong weathering and clay mineral formation with significant porosity reduction ( Fig.…”