Not Giving Physics the Slip

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Science  17 Aug 2001:
Vol. 293, Issue 5533, pp. 1223
DOI: 10.1126/science.293.5533.1223c

Great earthquakes (magnitude > 8) rupture over large distances in such a way that the amount of horizontal displacement (rupture length) between the two sides of the fault can be greater than the amount of vertical displacement (rupture width). Essentially, the rupture width cannot go any deeper than the base of the brittle crust, but the rupture length seems to be unlimited. This observation seems to defy physical principles of fracture mechanics observed in the laboratory.

Now, a study by Shaw and Scholz may resolve this apparent inconsistency. They modeled a great earthquake rupture in three dimensions with two layers of different frictional strength. Friction helps to determine how far a fault will slip; when friction decreases with increasing slip or slip rate, a fault will stick and slip to produce an earthquake, but if friction increases with increasing slip or slip rate, a fault will simply creep along. In simulations, the rupture length is related to a kinetic effect; slip pulses take a long time to build to their maximum intensity and then take a long time to dissipate. Thus, for a great earthquake, the slip pulses can move over long distances, and the maximum slip can occur far from the epicenter. Thus there is nothing fundamentally different about the physics of a small-to-large earthquake as compared with great earthquakes. — LR

Geophys. Res. Lett. 28, 2991 (2001).

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