Diverse Slip Behavior of the Banyak Islands Subsegment of the Sunda Megathrust in Sumatra, Indonesia

Nearly every type of slip behavior of which megathrusts are known to be capable of has been observed within a narrow similar to 75-km-wide strip of the Sunda megathrust-the Banyak Islands subsegment. The diverse list of recorded slip events starts with the great 1861 M-W similar to 8.5 earthquake and includes the 1907 M-W similar to 8.2 shallow tsunami earthquake, the 1966-1981 slow slip event, the great 2005 M-W 8.6 Nias-Simeulue earthquake and associated afterslip, many small (M < 6) to moderate (6 <= M < 7) earthquakes, and the large 6 April 2010 M-W 7.8 Banyak Islands earthquake. In this paper we map out the spatial and temporal relationships between these slip events to search for a pattern and possible controls on slip behavior. We use GPS and coral geodetic data to derive a coseismic slip distribution for the relatively understudied 2010 event and find that this event fits like a puzzle piece into a low slip patch left by the 2005 event. We compare the recent slip sequence with the historical sequence associated with the 1861 event and find that the modern slip pattern could be a repeat of the historical slip pattern, possibly suggesting the importance of stationary fault properties in controlling slip. The diverse set of slip events mostly fit our expectations within depth-dependent rupture zones; however, the overlaps between events of different slip types may complicate this conceptual model. Along strike, we suggest that a subducting fracture zone could act to diversify the slip behavior, and we explore possible mechanisms for this slip control. Plain Language Summary Where one tectonic plate is sliding or thrusting under another, the fault marking the boundary between them is a megathrust. For extended periods of time the plates are stuck together ("locked"), building up energy. This energy can be released rapidly, creating earthquakes, and also more slowly during slow slip events and afterslip. Mapping out the location, style, and magnitude of past slip events is one of the main methods to forecast where and how large future earthquakes could be. In this study we map out the recent slip history of one unique section of the Sunda megathrust, which has experienced nearly all types of slip that we know megathrusts are capable of. We find that the 2010 large magnitude 7.8 Banyak Islands earthquake slipped an area that did not slip much during a larger magnitude 8.6 earthquake in 2005, essentially filling in the missing slip. Our results mostly confirm the general relationships between fault depth and slip style. Lastly, we explore ways in which features on the megathrust inherited from the colliding plates could control the type of slip. We suggest fracture zones in the downgoing plate may complicate the slip history in this section of the megathrust.