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Published August 10, 2012 | Supplemental Material
Journal Article Open

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


Seismological observations of the 2012 moment magnitude 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 occurred on distinct planes in an orthogonal conjugate fault system, with relatively slow rupture speed. The east-southeast–west-northwest ruptures add a new dimension to the seismotectonics of the Wharton Basin, which was previously thought to be controlled by north-south strike-slip faulting. The rupture turned twice into the compressive quadrant, against the preferred branching direction predicted by dynamic Coulomb stress calculations. Orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure-insensitive strength of the deep oceanic lithosphere.

Additional Information

© 2012 American Association for the Advancement of Science. Received 30 April 2012; accepted 5 July 2012. Published Online July 19 2012. This research was supported by NSF grant EAR-1015704, by the Gordon and Betty Moore Foundation, and by the Southern California Earthquake Center (SCEC), which is funded by NSF Cooperative Agreement EAR-0106924 and USGS Cooperative Agreement 02HQAG0008. The Japanese Hi-net (www.hinet.bosai.go.jp) and the European ORFEUS (www.orfeus-eu.org) data centers were used to access the broadband seismograms. The magnetic anomalies are from the EMAG2 database available at the National Geophysical Data Center (www.ngdc.noaa.gov). The satellite gravity anomaly data are from the UCSD TOPEX v. 18.1 database. The multibeam bathymetry from the KNOX06RR cruise is available at Marine Geoscience Data System (www.marine-geo.org). We thank R.-C. Lien and B. Ma for providing the Roger Revelle (RR1201) multibeam data from the DYNAMO cruise. We thank H. Kanamori for valuable discussions about this event. This paper is Caltech Tectonics Observatory contribution 215, Caltech Seismo Lab contribution 10078, and SCEC contribution 1656.

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