Transport properties and dynamic processes in a fault zone from samples recovered from TCDP Hole B of the Taiwan Chelungpu Fault Drilling Project

Abstract

[1] We measured transport properties at a confining pressure of 60 MPa in core samples from the fault zone in Hole B of the Taiwan Chelungpu Fault Drilling Project (TCDP). Permeability and specific storage of the fault gouge range from 3 Â 10 À15 to 1 Â 10 À17 m 2 and from 2 Â 10 À10 to 7 Â 10 À10 Pa À1 , respectively, and the measured hydraulic diffusivity was 6 Â 10 À5 m 2 /s, which is consistent with the data measured in situ. Numerical analysis of the thermal pressurization mechanism during the 1999 Chi-Chi earthquake using laboratory measured transport and frictional properties showed that pore pressure at the fault zone increased dramatically during slip, whereas temperature increased only moderately to 400°C at the end of slip. The results indicate that dehydration of interlayer water in smectite is plausibly caused by frictional heating, although such dehydration does not influence fault weakening. The decomposition reactions of other minerals are difficult to explain for only one slip event. A magnetic susceptibility anomaly observed in the fault zone is consistent with the modeling results, although low contents of inorganic carbon and clay minerals are not. We concluded that these inconsistencies can possibly be explained by the combined effects of enhancement of chemical reactions by mechanochemical influences and periodic movement on the Chelungpu fault. High-temperature water-rock interactions are also a possible explanation for inconsistencies.

Fluid transport properties in sediments and their role in large slip near the surface of the plate boundary fault in the Japan Trench

“…The permeability of 10 −20 m 2 in the fault core in the Japan Trench is much smaller than at other active faults with the same effective pressure conditions. The permeability gap between the fault core and the overlying fault breccia or fracture zone is smaller than at other active faults in igneous rock Wibberley and Shimamoto, 2003;Tsutsumi et al, 2004), although a similar small permeability gap has been observed in the Nankai Trough splay fault and the Chelungpu fault (Ikari et al, 2009;Tanikawa et al, 2009) in sedimentary rocks. The variation of the permeability gap might be controlled by host rocks, such that breccia and fractures formed in sediments can be more easily compacted to decrease the permeability than similar features in igneous rocks.…”

“…The notable characteristics of the shallow part of the plate boundary are very low hydraulic diffusivity and low permeability, which are much smaller than for other active faults (e.g., hydraulic diffusivities of 10 −4 m 2 s −1 for the Chelungpu fault, Tanikawa et al, 2009; and 10 −3 m 2 s −1 for the Median Tectonic Line in Japan, Wibberley, 2002). Our numerical modeling that incorporates this fault zone characteristic indicates that thermal pressurization can occur at shallower depths from 820 to 4000 mbsf on the plate boundary.…”

“…Lacking physical fluid transport property data, Mitsui et al (2012a) relied on previously published data from a representative active fault. However, published fluid transport properties from fault zones have varied widely according to host rocks and tectonic settings (Noda and Shimamoto, 2005;Mizoguchi et al, 2008;Tanikawa et al, 2009) as well as pressure and temperature conditions (Wibberley, 2002;Faulkner and Rutter, 2000). Pore compressibility and specific storage in porous media have a strong influence on the pore pressure response through poro-elastic deformation (Wang, 2000), although these parameters for fault rocks are not well known (Wibberley and Shimamoto, 2003;Tanikawa et al, 2009).…”

Geochemical and mineralogical characteristics of fault gouge in the Median Tectonic Line, Japan: evidence for earthquake slip

“…Thermal signals recorded in the slip-zone minerals (Mishima et al 2006;Hirono et al 2007) and the low permeability of the fault zone (Doan et al 2006;Tanikawa et al 2009) strongly suggest that thermal pressurization took place during the earthquake (Ishikawa et al 2008). Geochemical analyses of the slip-zone rocks accompanied with generation of pseudotachylite in an ancient megasplay fault in the Shimanto accretionary complex (Mukoyoshi et al 2006) are also indicative of fluid-rock interactions at >350°C (Honda et al 2011).…”

Specific heat capacity and thermal diffusivity and their temperature dependencies in a rock sample from adjacent to the Taiwan Chelungpu fault

“…Thus, thermal pressurization potentially played a significant role during the earthquake. Tanikawa and Shimamoto [2009] and Tanikawa et al [2009] performed a numerical analysis of the thermal pressurization mechanism during the earthquake by using experimentally determined values for the frictional and transport properties of samples from the Taiwan Chelungpu Fault Drilling Project (TCDP). Their results support the inference that thermal pressurization contributed to fault weakening during the earthquake.…”