Crustal Structure Along The Central Sunda Margin, Indonesia
The plate boundary off Indonesia was investigated using a number of geophysical techniques and data. The work concentrated on the structural and tectonic differences along the central part of this 5600 km long margin. The subduction zone marks the collision of the Indian-Australian and the Eurasian plates and displays a significant variation of trench curvature resulting in areas of normal and of oblique subduction. A combined interpretation of marine seismic wide-angle and reflection data yields the subduction zone geometry. Traveltime analysis of the wide-angle data incorporated the results from the migrated MCS data for the shallow structure of the lines. The resulting velocity field is further constrained by gravity modelling and synthetic data. The Moho reflection of the downgoing slab could be verified to a depth of more than 30 km. The frontal part of the prism is experiencing active accretion in between the deformation front and an active backstop structure, which separates the accretionary domain from the outer high. Velocities underneath the outer high are fairly low, suggesting a sedimentary origin. Adjacent to the highly deformed outer high lies the undisturbed forearc basin. A significant change of the Moho depth underneath the forearc basin is observed: A shallow Moho is present underneath the Javanese forearc domain, while the crust underneath the forearc off Sumatra is more continental in nature. From these results the dominant role of the upper plate geometry and buttress in the evolution of this subduction zone is unraveled.