![]() ![]() Relative plate motion between the Indo-Australia and Sunda plates is rapid, decreasing from roughly 63 mm/year near the southern tip of Sumatra (Australia relative to Sunda) to 44 mm/year north of Andaman Islands (India relative to Sunda) and rotating counterclockwise to the northwest, so that relative motion near Jakarta is nearly trench-normal but becomes nearly trench-parallel near Myanmar. The Sumatra Fault, a major transform structure that bisects Sumatra, accommodates the northwest-increasing lateral component of relative plate motion. This convergence is responsible for the intense seismicity and volcanism in Sumatra. ![]() The Sumatra-Andaman portion of the collision zone forms a subduction zone megathrust plate boundary, the Sunda-Java trench, which accommodates convergence between the Indo-Australia and Sunda plates. ![]() The plate boundary southwest of Sumatra is part of a long tectonic collision zone that extends over 8000 km from Papua in the east to the Himalayan front in the west. Tectonic Summary Seismotectonics of the Sumatra Region ![]()
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