Sumatra Island is located in the path of volcano (NW-SE). Sumatra volcanic arc was formed by the meeting of two plates, the Indo-Australian plate which plunge down into Eurasian plate. The converging between the two plates as more detailed formed tectonic elements as follow:
• Active subduction zone, manifested by the Java-Sumatra Trench.
• Non-magmatic arc as accretionary wedge that formed island of Nias, Simeule Island, Mentawai Islands, etc..
• Fore arc basin, manifested by Sibolga Basin and Bengkulu Basin.
• Magmatic arc, indicated by the Barisan Mountains. Volcanoes located in the Barisan Mountains including Mount Merapi, Mount Kerinci, etc..
• Back arc basin, manifested by the Malacca Straits.
• Continental shelf of Sundaland.
Structure Map of Sumatra Island (Darman & Sidi, 2000)
Important symptoms that occur in Sumatra, in addition to that described above is the presence of horizontal Sumatra fault, known as the Sumatra Fault System (SFS) which divides the island of Sumatra, and following the path of the Barisan Mountains from Aceh to the Sunda Strait. There are two thoughts about SFS:
• Allegedly as a consequence of oblique subduction occurred in Sumatera (Katili, 1985).
• The movement was done by collision between India-Eurasia plate which extruded blocks of Southeast Asia toward Southeast (Tapponier, 1982).
In general, the process of Barisan Mountains uplifting began in Late Miocene, probably reached its peak at the boundary between the Miocene-Pliocene. This uplifting process is not consistently going on until now as estimated by recent geological features followed by the pattern of tectonics in the Early Pleistocene. Tectonic activity along the island formed massive geanticlines that causing the temperature rise related to rapid intrusion of accumulated magma underneath. It is characterized by increasing of both volcanic activity and lateral movement along Sumatra Fault System. All active tectonic activity over the Sumatra region is considered as the main source of recent earthquakes.
