The Great Sumatran fault, also known as Semangko fault, is a large strike-slip fault running the entire length of the island of Sumatra. This Indonesian island is located in a highly seismic area of the world, including a subduction zone off the west coast of the island. The Great Sumatran fault zone accommodates most of the strike-slip motion associated with the oblique convergence between the Indo-Australian plate and Eurasian plate The fault ends in the north near the city of Banda Aceh, which was devastated in the 2004 Indian Ocean earthquake.

Geologic significance

The Great Sumatran fault is part of the system where strain partitioning was first described in plate tectonics. The convergence between the Indo-Australian plate and the Sunda plate is not perpendicular to the plate boundary in this region. Instead, the two plates move at an oblique angle. Most of the convergent strain is accommodated by thrust motion at the plate boundary "megathrust" fault that defines the Sunda Trench. But the oblique motion (the part of the plate motion parallel to the plate boundary) is accommodated by the Great Sumatran fault, which runs along the volcanic Sunda Arc. The area between the main plate boundary thrust fault and the Great Sumatran fault forms a "sliver plate" that includes the entire offshore forearc, forearc islands, and the portion of Sumatra west of the Great Sumatran fault. This sliver plate is not a single rigid bloc, and the details of its internal deformation are under active investigation.

Earthquakes

Listed from northwest to southeast: