The island of Taiwan lies in a complex tectonic area between the Yangtze Plate to the west and north, the Okinawa Plate on the north-east, and the Philippine Mobile Belt on the east and south. The upper part of the crust on the island is primarily made up of a series of terranes, mostly old island arcs which have been forced together by the collision of the forerunners of the Eurasian Plate and the Philippine Sea Plate. These have been further uplifted as a result of the detachment of a portion of the Eurasian Plate as it was subducted beneath remnants of the Philippine Sea Plate, a process which left the crust under Taiwan more buoyant.
The east and south of Taiwan are a complex system of belts formed by, and part of the zone of, active collision between the North Luzon Trough portion of the Luzon Volcanic Arc and South China, where accreted portions of the Luzon Arc and Luzon forearc form the eastern Coastal Range and parallel inland Longitudinal Valley of Taiwan respectively.
The major seismic faults in Taiwan correspond to the various suture zones between the various terranes. These have produced major quakes throughout the history of the island. On 21 September 1999, a 7.3 quake known as the "921 earthquake" occurred. The seismic hazard map for Taiwan by the USGS shows 9/10 of the island as the highest rating (most hazardous).
On 4 March 2010 at about 01:20 UTC, a magnitude 6.4 earthquake hit southern Taiwan.