HR: 0830h
AN: T41D-0251    [PDF]
TI: Acoustic Emission Analysis of Stick Slip Behavior on Rough and Smooth Fractures in Westerly Granite
AU: * Thompson, B D
EM: B.Thompson@liv.ac.uk
AF: Dept. Earth Science, University of Liverpool, 4 Brownlow Street, Liverpool, L69 3GP United Kingdom
AU: Young, R P
EM: paul.young@utoronto.ca
AF: Dept. Earth Science, University of Liverpool, 4 Brownlow Street, Liverpool, L69 3GP United Kingdom
AU: Young, R P
EM: paul.young@utoronto.ca
AF: Lassonde Institute, University of Toronto, Rm 119, 170 College Street, Toronto, ON M5S 3E3 Canada
AU: Lockner, D A
EM: dlockner@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd, Menlo Pk, CA 94025 United States
AB: We present results from stick slip experiments on a rough and a smooth fault, and use Acoustic Emission (AE) data to make a comparison between the nature of slip on these two surfaces. Two Westerly Granite cores were pre-fractured to represent rough and smooth end member models of fracture surface geometry. One core featured a rough, natural fracture which was propagated quasi-statically by triaxial loading (under AE- feedback control). The second core contained a saw-cut fracture, the surfaces of which were hand lapped to produce a smooth finish. The pre-fractured cores were triaxially loaded to induce stick slip, at a confining stress of 150 MPa. In the rough fractured sample, one stick slip event was recorded at an axial stress of 625 MPa. During a five minute period about this slip, over 4000 AE events were triggered. A marked contrast is seen for slip on the smooth fractured sample, where a total of three discrete slip events occurred, at axial stresses of 380, 400 and 460 MPa. These slip events are characterized by a seismic quiescence; only 90 AE events were triggered during the five minute period about the final slip event. This extremely large difference in the amount of AE activity observed between slip on a rough and smooth fracture can be explained, as expected, by the presence of interlocking asperities on the rough fracture surface. In order to further analyze the characteristics of stick slip, we locate AE hypocenters to identify nucleation sites, calculate b-values, and resolve AE focal mechanisms to investigate the fundamental micromechanical processes operating on smooth and rough fracture surfaces.
DE: 7209 Earthquake dynamics and mechanics
DE: 8010 Fractures and faults
SC: Tectonophysics [T]
MN: 2003 Fall Meeting