HR: 0830h
AN: T41C-0231    [PDF]
TI: Olivine Friction at the Base of the Seismogenic Zone
AU: * Boettcher, M S
EM: margaret@whoi.edu
AF: MIT/WHOI Joint Program, Clark S. 275B, MS#24 Woods Hole Oceanographic Institution, Woods Hole, MA 02543
AU: Hirth, G
EM: ghirth@whoi.edu
AF: Dept. of Marine Geology and Geophysics, Woods Hole Oceanographic Institution, Mclean 208, MS#8, Woods Hole, MA 02543
AU: Evans, B
EM: briaevans@mit.edu
AF: Dept. of Earth and Planetary Sciences, Massachusetts Institute of Technology, 54-718, Cambridge, MA 02142
AB: The frictional properties at the base of the seismogenic zone in oceanic lithosphere are fundamental to our understanding of oceanic earthquake processes. While the composition of the oceanic lithosphere is probably the simplest and most well constrained of any seismogenic region on Earth, few data on its frictional properties exist. We are investigating the strength and sliding stability of olivine aggregates at temperature and effective pressure conditions close to those at the base of the seismogenic zone on a typical transform fault. We have conducted triaxial compression tests on dry olivine powder ($38-60 \ \mu$m particles) at effective pressures of $P_{\rm{eff}} = P_{\rm{c}} - P_{\rm{f}} = 50, \ 200, \ \& \ 300$ MPa using argon as a pore fluid medium, temperatures of $T = 800^{\circ}\rm{C} \ \& \ 1000^{\circ}\rm{C}$, and strain rates of $\dot{\epsilon} = 3 \times 10^{-5} \ \& \ 3 \times 10^{-4}$. For all experiments, strain became localized on faults and strain-rate steps showed velocity-weakening behavior. Stick-slip events were observed at all temperatures up to 1000$^{\circ}$C, with a greater tendency towards instability (i.e. more stick-slip events) at the higher strain rate. By contrast, previous laboratory work by Stesky et al. (1974) found stable sliding for olivine at temperatures above 200$^{\circ}$C. Our experiments are consistent with seismic data, which find that earthquake hypocenters regularly occur to temperatures well above 200$^{\circ}$C, regularly to near the 600$^{\circ}$C isotherm.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 5104 Fracture and flow
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
DE: 8159 Rheology--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting