HR: 13:55h
AN: S13D-02    [Abstracts]
TI: Insights on the Physics of Earthquakes from Laboratory Stick-Slip Friction in Conjunction with a Dynamic Rupture Model
AU: * McGarr, A
EM: mcgarr@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Fletcher, J B
EM: jfletcher@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Beeler, N
EM: nbeeler@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AB: Comparing laboratory friction results to corresponding parameters measured for earthquakes can yield key insights concerning the question of whether the physics of large and small earthquakes differ. Measurements made during large-scale, biaxial stick-slip friction measurements in the laboratory are effective for predicting many earthquake source parameters including the maximum slips and maximum slip rates within the fault zone of major earthquakes, as well as apparent stress. To relate the laboratory measurements to their earthquake counterparts, the laboratory results are multiplied by two adjustment factors, one for stress and the other for stiffness. The stress adjustment accounts for the difference between loading stresses in the laboratory and those at seismogenic depths in the crust. The stiffness adjustment involves replacing the laboratory fault with an equivalent-stiffness buried circular crack. These adjustments render the laboratory measurements in agreement, within a factor of two, of those determined using slip models of large earthquakes. Using the dynamic rupture model developed by Madariaga (1976) and Boatwright (1980), additional comparisons of seismic rupture processes between laboratory events and earthquakes can be drawn. Laboratory estimates of fracture energy density, typically of the order of several J/m2, can be extrapolated up to those of major earthquakes, approximately 1 MJ/m2. Similarly, this dynamic rupture model can be applied to the laboratory data to investigate several aspects of the energy changes that take place during earthquakes. First, the rupture model indicates that the seismic energy flux adjacent to an earthquake fault surface consists of the seismic energy radiated into the far-field plus the energy change associated with the static stress drop; the ratio of these two energies depends only on the rupture speed. Second, the laboratory results can be used in conjunction with the rupture model to estimate the components of the energy budget of an earthquake. (Released energy=radiated energy+fracture energy+frictional energy) It turns out that of the released elastic strain energy, the vast majority is consumed in overcoming friction. Returning to the question of whether small and large earthquakes differ in terms of their rupture physics, the well-defined relationships between the parameters of laboratory events and their earthquake counterparts suggest that the source processes of small and large earthquakes are much the same as those in laboratory friction experiments. If so, then the strength of the seismogenic zone plays the key role in determining the peak slip rate and the apparent stress.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: 2007 Fall Meeting