Overriding plate controls spatial distribution of megathrust earthquakes in the Sunda-Andaman subduction zone

The historic record of large megathrust earthquakes suggests that the potential for great destructive events is much larger for Sumatra than Java. Bouguer gravity anomalies correlate well with the occurrence of large megathrust earthquakes in the Sunda subduction zone; negative anomalies mark segments characterized by larger earthquakes while positive anomalies indicate lower seismic potential. Thermal models and structural constraints derived from seismic and gravity data are used to explain the seismogenic behaviour in the Sunda subduction zone. With respect to Java, oblique subduction of young oceanic crust shifts the seismogenic coupling zone roughly 40 km trenchward offshore of northern Sumatra and increases the width of the locked megathrust. A prominent positive gravity anomaly offshore of Java is caused by a shallow mantle wedge underlying the forearc basin. A serpentinized mantle wedge would limit the width of the coupling zone off Java to only 30-40 km, compared to > 120 km offshore of Sumatra. Sumatra remains therefore the most vulnerable site for future megathrust earthquakes, while the shallow mantle wedge may limit the violence of rupture off Java. (c) 2006 Elsevier B.V. All rights reserved.