HR: 0800h
AN: S41A-0936    [Abstracts]
TI: Fracture propagation, stable sliding and stick slip by pore pressurizing a fault gouge analog
AU: * Schubnel, A
EM: alexandre.schubnel@utoronto.ca
AF: Lassonde Institute, University of Toronto 170 College Street, Toronto, On M5S3E3 Canada
AU: Thompson, B
EM: B.Thompson@liverpool.ac.uk
AF: Lassonde Institute, University of Toronto 170 College Street, Toronto, On M5S3E3 Canada
AU: Fortin, J
EM: fortin@geologie.ens.fr
AF: Laboratoire de Geologie, Ecole Normale Superieure 24 rue Lhomond, Paris, 75005 France
AU: Young, R
EM: paul.young@utoronto.ca
AF: Lassonde Institute, University of Toronto 170 College Street, Toronto, On M5S3E3 Canada
AB: Thermal pressurization of pore fluid has recently been proposed as a mechanism for velocity weakening of fault gouge materials (Mase et al., [1984]). Rice [1992] and Miller [2003] have also suggested the earthquake cycle is mainly a pore pressure cycle. A Fontainebleau sandstone sample of 14% porosity was deformed tri-axially at the Laboratoire de G\'eologie of ENS Paris. A confining pressure of 100 MPa was used, in saturated conditions. Acoutic properties were monitored through 14 compressional wave piezoceramic transducers (PZT) which were directly glued onto the sample cylindrical surface. During the first cycle, differential stress was slowly raised to 250 MPa. Subsequently, an increase in pore pressure induced brittle failure at Pp=72MPa, with a stress drop of 150 MPa. In addition to triggered Acoustic Emissions (AE), the entire conitinuous ultrasonic waveform of the rupture was recorded. Over 10 000 AE were located, demonstrating the evolution of a fracture nucleation patch of order 1cc. Measured permeability showed that the nucleation of a damage/fault zone induced a drastic reduction in permeability, which could explain the many aftershocks that were observed after the main fracture propagation. Elastic wave velocities also show the extent of permanent damage in the rock. During the second cycle, we re-loaded the fractured sample up to a differential stress of 150 MPa. An initial slow pore pressurization induced stable sliding from 65 to 70 MPa. The pore pressure was then reduced, and a fast pore pressure pulse applied, (from 0 to 80 MPa in two seconds) inducing major stick slip (with an associated stress drop of 50 MPa). Again, in this cycle, more than 15 000 AE were located and aftershocks due to pore pressure re-equilibration were observed, post failure. In this preliminary study, we present a non-exhaustive compilation of data obtained during this pore pressure cycling experiment, including AE locations, continuous ultrasonic waveform summaries, wavespeed and permeability variations, and other mechanical data. Such a complete set of experimental data is, to our knowledge, the first to be obtained and could provide a more complete understanding of the earthquake cycle.
UR: http://www.lassondeinstitute.utoronto.ca/young/people/alex2.htm
DE: 8159 Rheology--crust and lithosphere
DE: 5104 Fracture and flow
DE: 5114 Permeability and porosity
DE: 7209 Earthquake dynamics and mechanics
DE: 3902 Creep and deformation
SC: Seismology [S]
MN: 2004 AGU Fall Meeting