HR: 11:20h
AN: S32B-05 INVITED     [Abstracts]
TI: Friction Constitutive Properties of Fault Zone Materials
AU: * Marone, C
EM: cjm@geosc.psu.edu
AF: Penn. State University, Dept. of Geosciences, 536 Deike Bld., University Park, PA 16802 United States
AU: Saffer, D
S32B-05 AF: Penn. State University, Dept. of Geosciences, 536 Deike Bld., University Park, PA 16802 United States
AU: McKieran, A
S32B-05 AF: Penn. State University, Dept. of Geosciences, 536 Deike Bld., University Park, PA 16802 United States
AU: Rowe, C
S32B-05 AF: UC Santa Cruz, Dept. of Earth Sciences, Santa Cruz, CA 95064 United States
AU: Samuelson, J
S32B-05 AF: Penn. State University, Dept. of Geosciences, 536 Deike Bld., University Park, PA 16802 United States
AB: A central problem in evaluating the relationship between fault zone properties and earthquake physics is a lack of detailed laboratory data for fault zone materials recovered from hypocentral depths. We report on a suite of experiments conducted on fault zone materials recovered from SAFOD phase 1 drilling, the Ghost Rocks Formation Kodiak Islands Alaska, and ODP drilling. The Ghost Rocks Formation underwent deformation at 12-14 km in a subduction thrust and samples consist of cataclasite and marine sediments similar to that which forms fault gouge in subduction zones. Samples from San Andreas Drilling range in depth from 1.4 km to 3.1 km and include wall rock and material from sub-faults of the San Andreas system. Layers of intact and powdered fault rock were sheared in the double-direct shear geometry, under shear velocity boundary conditions at constant normal stress, and within rough rigid forcing blocks using a servo-controlled testing machine. Normal stress and shear velocity ranged from 5 to 100 MPa and 1-300 micron/s. Intact slabs of fault rock were cut to 5 cm x 5 cm x 4-mm thick wafers for insertion in the double-direct shear geometry. Post-experiment examination of the sheared intact slabs shows that the sample remains intact and that shear is accommodated by a combination of pervasive strain and localized shear. Experiments were conducted at room temperature (22-24 C) under controlled relative humidity and saturated conditions. Changes in porosity are monitored continuously as a function of slip and time. We employed a normal stress stepping procedure to efficiently evaluate the Coulomb failure envelope and friction constitutive properties at a range of fault depths with limited sample material. SAFOD data show consistent values of the coefficient of sliding friction (we assume zero cohesion for the granulated layers) ranging from 0.57 to 0.63. At each normal stress, samples recovered from greater depth exhibit slightly lower friction values compared to the granite from 1.4 km. The frictional strength of the SAFOD samples are comparable to pure quartz powder and stronger than an illite shale. SAFOD core from 3062+ m contain shear textures and small amounts of phyllosilicates, which is consistent with their slightly lower strengths. The data for shear of the intact Ghost Rocks Formation show friction values in the range 0.34 to 0.44, which is consistent with the high clay contents in those samples. Velocity stepping tests indicate that steady-state friction values are reached and that the fault rocks exhibit slip-rate and history-dependent friction behavior similar to that documented for simulated fault gouge. A sudden increase in load point velocity results in an immediate increase in friction followed by a displacement-dependent decay to a new steady-state level. Measurements of steady-state friction as a function of slip velocity show velocity weakening frictional behavior for some SAFOD and ODP materials at low normal stress. In these cases, friction velocity dependence increases with increasing normal stress and becomes positive for normal stresses above 40 MPa. Samples from the Ghost Rocks Formation exhibit velocity strengthening for the full range of conditions studied. We report friction constitutive parameters determined by modeling data using the full rate and state friction law and elastic coupling between the testing apparatus and shearing layers.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 5104 Fracture and flow
DE: 7209 Earthquake dynamics (1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Seismology [S]
MN: Fall Meeting 2005