China - Taiwan Province

USGS earthquake bulletin: Taiwan 31 Mar 2002

Situation Report
Originally published
Date-Time 2002 03 31 06:52:50 UTC
Location 24.41N 122.21E
Depth 33.0 kilometers
Magnitude 7.1
Reference 50 miles (80 km) NE of Hua-lien, Taiwan

The following is a release by the United States Geological Survey, National Earthquake Information Center: A major earthquake occurred NEAR THE NORTHEAST COAST OF TAIWAN, about 65 miles (100 km) southeast of Taipei at 11:52 PM MST, Mar 30, 2002 (Mar 31 at 2:52 PM local time in Taiwan). The magnitude and location may be revised when additional data and further analysis results are available. There have been some reports of damage and casualties in northeastern Taiwan.

Tectonic setting

This thrust earthquake occurred off the north-east shore of the island of Taiwan in a tectonicly complex region known as the Taiwan Collision Zone. This region is highly seismic. There are an average of five earthquakes per year with magnitude 5 or greater occurring within a 1 by 1 degree zone surrounding the epicenter. The high seismicity results from the convergence of the Philippine Sea plate and the Eurasian plate. The Philippine plate is moving NW at a rate of about 7 cm per year relative to the Eurasian plate. The complex region near the epicenter contains several substantial tectonic features including, the Ryukyu trench, Manila trench, and the Okinawa trough.

Given the earthquake's fault mechanism and depth, it likely resulted from slip on the boundary between the subducting Philippine plate and the overlying Eurasian plate (see the cross-section link to the left). The surface expression of this contact is the east-west trending Ryukyu trench which is about 200 kilometers southeast of the epicenter.

The tectonic environment of this earthquake differs from that of the more destructive magnitude 7.7 earthquake that occurred on September 20, 1999; the latter earthquake occurred in the crust of the Eurasian plate within the island of Taiwan.