Sibling earthquakes generated within a persistent rupture barrier on the Sunda megathrust under Simeulue Island

A section of the Sunda megathrust underneath Simeulue is known to persistently halt rupture propagation of great earthquakes, including those in 2004 (M_w 9.2) and 2005 (M_w 8.6). Yet the same section generated large earthquakes in 2002 (M_w 7.3) and 2008 (M_w 7.4). To date, few studies have investigated the 2002 and 2008 events, and none have satisfactorily located or explained them. Using near-field InSAR, GPS, and coral geodetic data, we find that the slip distributions of the two events are not identical but do show a close resemblance and largely overlap. We thus consider these earthquakes “siblings” that were generated by an anomalous “parent” feature of the megathrust. We suggest that this parent feature is a locked asperity surrounded by the otherwise partially creeping Simeulue section, perhaps structurally controlled by a broad morphological high on the megathrust.