Earthquake in a Maze: Compressional Rupture Branching During the 2012 Mw 8.6 Sumatra Earthquake

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Science  19 Jul 2012:
DOI: 10.1126/science.1224030

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Seismological observations of the 2012 Mw 8.6 Sumatra earthquake reveal unprecedented complexity of dynamic rupture. The surprisingly large magnitude results from the combination of deep extent, high stress drop, and rupture of multiple faults. Back-projection source imaging indicates that the rupture occurs on distinct planes in an orthogonal conjugate fault system, with relatively slow rupture speed. The ESE-WNW ruptures add a new dimension to the seismotectonics of the Wharton Basin, which was previously thought to be controlled by N-S strike-slip faulting. The rupture turns twice into the compressive quadrant, against the preferred branching direction predicted by dynamic Coulomb stress calculations. Orthogonal faulting and compressional branching indicate that rupture is controlled by a pressure-insensitive strength of the deep oceanic lithosphere.

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