Sunda Strait marks the limit between Java trench frontal subduction and Sumatra trench oblique subduction. The right-lateral Central Sumatra fault accommodates the oblique subduction. It does not pass Sunda Strait but ends between Sumatra and Java in a complex pattern of dominantly normal faults associated with subsidence, seismicity, and volcanism. We examine the implications of this phenomenon in Sunda Strait and in the adjacent fore-arc basin and accretionary prism, which underwent north-south compression due to subduction, as well as east-west extension. We propose that the strait is a consequence of the northwestward motion of the southwestern Sumatra block along the Central Sumatra fault. We also propose that the extensional zone in the Sunda Strait widens considerably to the southwest, toward the trench, and changes into a composite zone of deformation affected by strike-slip as well as normal faulting.

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