Sumatra back arc basins including North, Central and South Sumatra basin. Sunda forearc basin, lying between the accreting non-volcanic outer-arc ridge with submerged segments, and the volcanic back arc of Sumatra.ģ.

Sunda outer-arc ridge, located along the active margin of the Sunda forearc basin and separate it from the trench slope.Ģ. In general the region can be divided into 6 regions (Fig. The basinal configuration of Sumatra is directly related to the presence of the subduction-induced non-volcanic forearc and the volcano-plutonic backarc, the morpho-structural backbone of the Island. This zone of oblique convergence is marked by the active Sunda Arc-Trench system which extends for more than 5000 km, from Burma in the north to where the Australian Plate is in collision with Eastern Indonesia in the south (Hamilton 1979). At the present-day, the Indian Ocean Plate is being subducted beneath the Eurasian Continental Plate in a N20oE direction at a rate of between 6 and 7 cm/yr (Fig. The Sumatra island is interpreted to be constructed by collision and suturing of discrete micrcontinents in late Pre-Tertiary times (Pulunggono and Cameron 1984, Barber 1985). At Diamond Point, in Aceh, this low eastern belt has a width of about 30 km its width increases to 150-200 km in central and south Sumatra. The eastern belt of the island is covered by broad, hilly tracts of Tertiary formations and alluvium lowlands. The slope towards the Indian Ocean is generally steep, consequently the west belt is mostly mountainous, with the exception of two lowland embayments in north Sumatra which are about 20 km wide. This region divides the west and the east coast. Its backbone is formed by the Barisan Range which runs along the western side. The main geographical trendlines of the island are rather simple.

Its width is about 100-200 km in the northern part and about 350 km in the southern part. The Sumatra Island has an area of about 435,000 km2, measuring 1650 km from Banda Aceh in the north to Tanjungkarang in the south. Sumatra Island is the northwest oriented physiographic expression, lied on the western edge of Sundaland, a southern extension of the Eruasian Continental Plate (Fig.

Sumatera indonesia