HR: 0800h
AN: S41B-0995    [Abstracts]
TI: Physical and Mechanical Properties of the Mozumi Fault, Japan: Petrophysics of a Fine-Grained Fault Zone
AU: Isaacs, A J
EM: angela.isaacs@usu.edu
AF: Department of Geology Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505
AU: * Evans, J P
EM: jpevans@cc.usu.edu
AF: Department of Geology Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505
AU: Kolesar, P T
EM: petes@cc.usu.edu
AF: Department of Geology Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505
AB: The Mozumi-Sokenobu fault, a right-lateral strike-slip fault in north-central Honshu, Japan is intersected by the Active Fault Survey Tunnel. This tunnel allows for direct observation of the fault at a depth of 300-400 m below the ground surface. Within the tunnel, the Mozumi fault cuts Jurassic Tetori Group sandstone and shale. We have characterized microstructures, mineralogy, geochemistry, and elastic properties of fault rock samples from the Mozumi fault. These data can be combined to illustrate the in-situ macroscopic hydro-mechanical structure of the fault. Core samples from the main Mozumi fault zone intersected by the Active Fault Survey Tunnel borehole A were analyzed and compared to wireline logs for a petrophysical study of the fault zone rocks. Microstructures, mineralogy, and geochemistry of Mozumi fault rocks indicate syn-tectonic fluid flow and multiple deformation events. Resistivity and sonic log values are depressed through the main fault zone. Likewise, the seismic p and s wave velocity values are decreased across the main fault relative to the surrounding rock. Calculated values for Young's modulus and Poisson's ratio fall at the top of or above the experimentally derived range for elastic moduli of siltstone, shale, and sandstone. Smaller scale variations across the fault zone itself are also present. Samples of foliated fault rocks containing predominantly muscovite have intermediate values for elastic moduli and seismic velocity relative to other fault zone samples used in this study. Fault rocks significantly depleted in oxides relative to host rock samples and containing mixed clays have higher resistivity than surrounding fault rocks and intermediate permeability values. These variations in physical and mechanical properties throughout the fault zone coincide with the complex fault-parallel combined conduit/barrier permeability structure of the Mozumi fault zone.
DE: 8111 Continental tectonics: strike-slip and transform
SC: Seismology [S]
MN: Fall Meeting 2005