Causes of Earthquakes in Taiwan

Taiwan is located at the intersection of the Philippines Sea Plate and the Euraisian Plate, which are part of the circum-Pacific volcano and seismic zone.  The Hualian-Taitung Valley is the boundary of these two plates. Over the years, the Philippines Sea Plate has moved to the north-west at the average velocity of 7 cm/year. The northern arc of Luzon Island, which is located in the west Philippines Sea Plate, collided with the edge of the Euraisian Plate 6 million years ago and elevated the Euraisuan Plate rapidly to form Taiwan’s Central Mountain Range. It’s like an extra large bulldozer, which is pushing the western Hualian-Taitung Valley and bending and arching the stratums, leading to even greater destruction and earthquakes.

Because the pushing force comes from the east, the faults in Taiwan are mainly trust faults. The crust of the eastern side of the faults is gradually moving upward and westward, and staking up on the western side. This is the basic background of Taiwan’s seismic activity.

An Introduction to Taiwan’s Active Faults

The research of the Central Geological Survey shows Taiwan now has 42 active faults; whereas the research of National Central University says Taiwan has 51 active faults. The difference between these two institutes is the fault determining difference. National Central University treats some faults as individual faults while Central Geological Survey treats as one fault.

Surrounding these active faults is the heavy earthquake zone. You can learn more about the distribution of Taiwan’s faults at http://cgsweb.moeacgs.gov.tw/result/Fault/web/web/images/C_activefault(800).jpg or http://140.115.123.45/ncufault.htm

The active faults in Taiwan can be classified as Type I Active Fault (AF1), Type II Active Fault (AF2) and Suspected Active Faults (AF3).  The definitions of these active faults are as follows:

Type II Active Faults (Late Pleistocene Active Faults)

	The fault has experienced displacement since the Holocene era (10,000 years ago)
	The fault displaced or crept modern structure
	The fault came with earthquakes.
	The fault displaced modern alluvium.
	Terrain monitoring proves the fault has creep activity.

Type II Active Faults (Late Pleistocene Active Faults)

	The fault has occurred displacement since Late Pleistocene era (100,000 years ago)
	The fault displaced terrace or tableland.

Suspected Active Faults (The existence, active age, re-active possibility of faults are suspected)

	The fault experienced displacement in the forth period stratum.
	The fault displaced the slow undulated laterite.
	The terrain showed the active fault’s symbol but lacked of geological proven data.

Heavy / Serious Earthquakes in Taiwan

Taiwan experiences more than 200 perceivable earthquakes every year. The following is a list of the stronger quakes resulting in greater economic loss or human suffering.