M 6.4 - 25 km SE of Yujing, Taiwan

Tectonic Summary

The February 5, 2016 M 6.4 earthquake east of Tainan in southern Taiwan occurred as the result of oblique thrust faulting at shallow-mid crustal depths (~ 20 km). Focal mechanisms indicate rupture occurred on a fault oriented either northwest-southeast, and dipping shallowly to the northeast, or on a north-south striking structure dipping steeply to the west. Taiwan lies in a region of complex tectonics, at the boundary between the Philippine Sea and Eurasia plates. To the north and east, the Philippine Sea plate subducts beneath Eurasia towards the north-northwest, along the Ryukyu Trench. South of the island, the South China Sea (on the the Eurasia plate) subducts to the east beneath the Philippine Sea plate at the Manila Trench. Moving north, subduction tectonics transition to arc-continent collision along the western side of Taiwan. At the location of the earthquake, the two plates converge in a northwest-southeast direction at a velocity of about 80 mm/yr.

Taiwan is the location of frequent seismicity, and 90 M 6.4+ events have occurred within 250 km of the February 5, 2016 event over the preceding century. Several of these earthquakes occurring beneath Taiwan (rather than in the subduction zone northeast of the island) have been destructive. A M 5.7 earthquake 70 km to the north of the February 2016 event in July 1998 caused 5 fatalities; a M 7.0 event in December 2006, 120 km to the south, caused 2 fatalities. The Chi-Chi earthquake (also Jiji, or 921 earthquake), a M 7.6 event in September 1999 just over 100 km north-northeast of the February 2016 event, caused widespread destruction and almost 2,500 fatalities. The 1999 event was the second deadliest earthquake in Taiwan history, after the April 1935 earthquake just north of Taichung, which caused over 3,200 fatalities. A M 7.3 earthquake in December 1941, between the cities of Tainan and Chiai and 55 km northwest of the February 2016 event, also caused several hundred fatalities.