Kinematics of Slip Partitioning in Sumatra

Abstract:

Published geological slip rates of the Sumatran Fault, slip vectors of Sunda megathrust earthquakes, and the geodetic velocity field of Sumatra and the forearc islands appear the require distributed and rapid stretching of the Sumatran forearc parallel to the Sunda Trench. We show that revised Sumatran Fault slip rates, earthquake slip vector azimuths, and the long-term geodetic velocity field are consistent instead with a non-deforming, rigid forearc block that overlies a heterogeneously coupled Sunda megathrust and is separated from the Sunda Block by the Sumatran Fault. Like previous studies, we conclude that rigid plate tectonics fails to describe the Sumatran subduction system; however, we attribute this failure to the well documented internal strain within the Eastern Indian Ocean lithosphere. We further constrain the along-strike variation in the rate of underthrusting of oceanic lithosphere beneath the Sumatran forearc, an important boundary condition for paleogeodetic studies of elastic strain accumulation within the forearc and the cycle of great Sunda megathrust earthquakes.