HR: 1340h
AN: T53B-1432    [Abstracts]
TI: Permeability Evolution During the Growth and Interaction of Localized Failure
AU: * Zhu, W
EM: wzhu@whoi.edu
AF: WHOI, MS8, Woods Hole, MA 02543
AU: Chen, T N
EM: tzchen@ic.sunysb.edu
AF: SUNY, Dept. Geosciences, Stony Brook, NY 11794
AU: Xiao, X
EM: xhxiao@mit.edu
AF: MIT, Dept. of EAPS, Cambridge, MA 02139
AU: Wong, T
EM: Teng-fong.Wong@stonybrook.edu
AF: SUNY, Dept. Geosciences, Stony Brook, NY 11794
AB: Generation and maintenance of high pore pressure in active tectonic environments critically depends on permeability, a dynamic physical parameter that is sensitive to pressure, temperature and stress. Experimental studies have shown that permeability can be significantly modified under hydrostatic or non-hydrostatic stresses. Under relatively low confinement and temperature, rocks fail by brittle faulting. In the brittle faulting regime, deformation is mainly localized in shear bands, which are usually developed at high angles to the maximum compression direction. Dilatancy and strain softening are usually accompanied by permeability enhancement. During an earthquake cycle, shear localization can provide conduits for pore fluid discharge. With increasing confining pressure and temperature, compaction localization develops in compactant porous sandstones. In the compaction localization regime, deformation is localized in compaction bands. These compaction bands, developed under relatively high confinements, are morphologically different from shear bands developed under low confinements. When a rock fails by compaction localization, an array of discrete bands or diffused zones are observed sub-perpendicular to maximum compression. It is demonstrated that the development of compaction bands generally induces significant permeability reduction and provides hydraulic barriers for pore pressure excess. An intriguing question is, at conditions where an intact porous rock fails by compaction localization, what type of dynamic hydromechanical behavior should we expect if the rock has a pre-existing fault? To address this question, we conducted experiments in which porous Bentheim sandstone samples were first deformed at an effective pressure of 5 MPa. After shear localization developed, we reloaded the sample and deformed it at effective pressures of 5-200 MPa. Our experimental results show that, at 5 MPa the sample shown stable sliding along the pre-existing shear-band. However, with the increasing confining pressure, compaction localization occurs in the pre-faulted rock. The compaction bands generally initiated at the pre-existing fault and gradually developed into a series of bands intersect the fault. Concomitant permeability and porosity evolution as functions of the initiation of shear localization, the interaction between the shear localization and compaction localization have important implications in pore pressure excess and earthquake generations in active margins.
DE: 5104 Fracture and flow
DE: 5114 Permeability and porosity
DE: 5139 Transport properties
DE: 8010 Fractures and faults
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Tectonophysics [T]
MN: Fall Meeting 2005