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Supershear rupture in a Mw 6.7 aftershock of the 2013 Sea of Okhotsk earthquake

Science  11 Jul 2014:
Vol. 345, Issue 6193, pp. 204-207
DOI: 10.1126/science.1252717

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Supershear rupture down below

Deep earthquakes occur in complex fault zones more than 70 kilometers below Earth's surface. Although they do not pose much of a hazard, they can still provide valuable insight into how earthquakes rupture. Zhan et al. found that a magnitude 6.7 aftershock of the largest deep earthquake recorded to date—the 2013 magnitude 8.3 Sea of Okhotsk earthquake—ruptured faster than the velocity of its seismic waves. This so-called “supershear” rupture shows that deep earthquakes have diverse rupture mechanisms and have several routes to dissipate energy.

Science, this issue p. 204

Abstract

Earthquake rupture speeds exceeding the shear-wave velocity have been reported for several shallow strike-slip events. Whether supershear rupture also can occur in deep earthquakes is unclear, because of their enigmatic faulting mechanism. Using empirical Green's functions in both regional and teleseismic waveforms, we observed supershear rupture during the 2013 moment magnitude (Mw) 6.7 deep earthquake beneath the Sea of Okhotsk, an aftershock of the large deep earthquake (Mw 8.3). The Mw 6.7 event ruptured downward along a steeply dipping fault plane at an average speed of 8 kilometers per second, suggesting efficient seismic energy generation. Comparing it to the highly dissipative 1994 Mw 8.3 Bolivia earthquake, the two events represent end members of deep earthquakes in terms of energy partitioning and imply that there is more than one rupture mechanism for deep earthquakes.

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