Abstract

A backprojection method is applied to the 27 February 2010 Mw 8.8 and 25 March 2012 Mw 7.1 Maule, Chile, earthquakes using high‐frequency (0.8–2 Hz) USArray data. During the 2010 event, highest energy release occurred north of the epicenter, with two subevents comprising this rupture. The gap between these subevents was about 100 km and 15 s, suggesting that P waves from the first subevent dynamically triggered the second subevent. This triggering can be explained as a consequence of stopping phases generated at the terminus of subevent 1, as the rupture encounters a region of low interseismic coupling. This argument is supported by the occurrence of the 2012 Mw 7.1 event, which is the largest interface earthquake since the 2010 mainshock and ruptured an area that completely filled the gap left from the mainshock. Seismic gaps, regions between the slip areas of past giant earthquakes, are known to have a higher potential for generating future large events. The results of this study show that a coseismic gap behaves similarly, and detailed imaging of rupture propagation can be used to identify areas that may produce large earthquakes. A comparable coseismic gap to the 2010 Chile gap is identified for the 2011 Mw 9.0 Tohoku, Japan, earthquake that may be the site of a large event in the near future.

Online Material: Figures showing point source synthetic tests for the back projection method, station location, and distribution of energy release.

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