Report

Rapid Acceleration Leads to Rapid Weakening in Earthquake-Like Laboratory Experiments

Science  05 Oct 2012:
Vol. 338, Issue 6103, pp. 101-105
DOI: 10.1126/science.1221195

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Grinding Out Earthquake Physics

Simulating earthquakes in the lab produces events that are often orders of magnitude lower in energy than large, damaging earthquakes; thus, it is unclear how well the behavior along these simulated faults extrapolates to the physics of large earthquakes. Chang et al. (p. 101; see the Perspective by Shimamoto and Togo) used a rotary apparatus that spins in tandem at high speeds with a disc-shaped rock sample, producing energies comparable to earthquakes of magnitudes 4 to 8. Experiments using both granite and dolomite samples suggest that the weakening of slip along faults during large earthquakes is a product of intense accelerations associated with the rupture event.

Abstract

After nucleation, a large earthquake propagates as an expanding rupture front along a fault. This front activates countless fault patches that slip by consuming energy stored in Earth’s crust. We simulated the slip of a fault patch by rapidly loading an experimental fault with energy stored in a spinning flywheel. The spontaneous evolution of strength, acceleration, and velocity indicates that our experiments are proxies of fault-patch behavior during earthquakes of moment magnitude (Mw) = 4 to 8. We show that seismically determined earthquake parameters (e.g., displacement, velocity, magnitude, or fracture energy) can be used to estimate the intensity of the energy release during an earthquake. Our experiments further indicate that high acceleration imposed by the earthquake’s rupture front quickens dynamic weakening by intense wear of the fault zone.

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