The 2006 Hengchun Earthquake and Tectonic Setting of Southern Taiwan

On 26 December 2006 at 12:26 local time, a magnitude 7.1 earthquake occurred 30 km southwest of Hengchun, Taiwan, at a focal depth of 10 km. The event is recorded as the sole M7-class earthquake in the region since 2000.01.01. Southern Taiwan lies at the active collision zone between the Eurasian Plate and the Philippine Sea Plate. Convergence rates reach approximately 8 cm per year, producing rapid crustal shortening and frequent seismicity. The Hengchun Peninsula occupies the southernmost exposed portion of the Taiwan orogen, where the north-trending Central Range transitions into the offshore Luzon Arc. Deformation is accommodated along the Longitudinal Valley Fault system to the east and a series of west-vergent thrust faults and folds that extend into the Taiwan Strait. The 2006 hypocenter is situated near the deformation front associated with the Manila Trench, where oceanic lithosphere of the South China Sea is being subducted eastward beneath the Philippine Sea Plate. The shallow depth and thrust mechanism of the 2006 mainshock are consistent with regional tectonics. Historical records document recurrent large earthquakes along the southern Taiwan coast, including events in 1943 and 1959 that produced similar offshore rupture patterns. Paleoseismic studies of uplifted marine terraces along the Hengchun coastline indicate recurrence intervals on the order of several hundred to a few thousand years for M7+ earthquakes. Post-event analyses confirmed that the rupture propagated along a low-angle thrust plane, generating a modest local tsunami and triggering submarine landslides that severed several international fiber-optic cables. These observations align with the known seismic and geomorphic hazards of an actively accreting forearc setting.

References

USGS Earthquake Catalog (event page for 2006-12-26 M7.1 Hengchun sequence).
Central Geological Survey, Taiwan, Active Fault Map and Tectonic Summary (2023 update).
Suppe, J. (1984). Kinematics of arc-continent collision, Taiwan. Geological Society of China.