Taiwan Earthquakes of September 1999

nisee

National Information Service for Earthquake Engineering
University of California, Berkeley

The Taiwan Earthquakes (Ji-Ji) of September, 1999

The devastating earthquakes which struck central Taiwan (the largest measured as 7.6 Richter by USGS and at a depth of 1.1 km by the Central Weather Bureau ROC) beginning on Monday, September 20 and the series of more than 9,000 aftershocks which have followed the first event have resulted in official estimates of 2,161 deaths, 8,736 injuries with approximately 150 people still listed as missing. There are over 60 km of surface faulting, substantial lateral displacements up to nine meters. Vertical displacements are large.

Seismically complicated, Taiwan is largely situated in a subduction zone between Phillippine Sea and Eurasian Plates. Although the east coast of the island is considered most seismically active the recent earthquakes occurred in the Central part of the island primarily on the Chelongpu fault. Several large thrust faults extend across the island as indicated in the accompanying map. Taiwan is extensively seismically instrumented and warnings were automatically sent to rescue officials immediately following the first earthquake. Preliminary acceleration maps are drawn. Because of the extensive instrumentation in Taiwan, it is expected that many strong motion records, especially near field records, will be available to the international scientific community. The ROC National Center for Earthquake Engineering is conducting engineering reconnaissance of earthquake effects and gradually publishing results including this epicenter map which was produced by the ROC Central Weather Bureau.

Professor Jack Moehle, Director of the Pacific Earthquake Engineering Research (PEER) Center, was part of a reconnaissance group now in Taiwan and sent the following initial information and photos. Subsequently, several other reconnaissance groups have been to Taiwan and selected reports are linked at the bottom of this page. (clicking on small image will link to a larger image)

A bridge constructed in 1980, south of the epicenter near Doulan. Abutment to the north (right side of this figure) moved toward the south. Seven foot diameter columns had been strengthened by encasing in very large piers to protect from impact damage in the river, leaving a short segment that failed in shear. The column nearest north failed in shear in the longitudinal direction. More southern piers showed some transverse motion in the shear failure. Bent caps completely severed from piers; spans collapsed to ground.

This building near Juahan was lifted several feet by the fault. Fault rupture runs just near the side of the building, down the alley. No apparent damage to the building.

Bridge built in 1990 near Juahan. Fault appears to have cut through bridge at a skew. Precast girder superstructure thrown southward at least ten feet, knocking adjacent spans off bent caps. Compression failure of south abutment and several spans lost.

Major cable-stayed bridge nearly completed near Mingjian. Shear cracking of bent caps, horizontal superstructure misalignments, hammering at superstructure joints, superstructure shear - compression failures, failure of a cable and severe flexural - compression spalling of pylon.

Damage to a concrete building: soft first stories, inadequate ties, column flexural failures, column shear failures, and many joint failures. There are many cases of weak-story collapses, column failures, and joint failures.

One of several bridges for which the fault ran beneath the bridge. The offset deformed the bridge with forces probably far exceeding those likely through inertial forces only. The piers, lightly reinforced, might be expected to have adequate strength for inertial effects, but not for deformations of the supporting earth.

Another bridge affected by faulting. In this case a series of simple spans on piers, several spans of which collapsed. One would not be surprised to find the spans became unseated and dropped from the piers. But what projected these spans so that they ended up overhanging the supports by several meters?

Suggested related sites include:

Preliminary Reconnaissance Journal: Narrative Account of Field Investigations by a PEER Reconnaissance Team
Taiwan-US Geotechnical Earthquake Engineering Reconnaissance Report
Kyoto University, Disaster Prevention Research Institute Quick Reconnaissance Report

January 6, 2006 EERC Library

	A bridge constructed in 1980, south of the epicenter near Doulan. Abutment to the north (right side of this figure) moved toward the south. Seven foot diameter columns had been strengthened by encasing in very large piers to protect from impact damage in the river, leaving a short segment that failed in shear. The column nearest north failed in shear in the longitudinal direction. More southern piers showed some transverse motion in the shear failure. Bent caps completely severed from piers; spans collapsed to ground.
	This building near Juahan was lifted several feet by the fault. Fault rupture runs just near the side of the building, down the alley. No apparent damage to the building.
	Bridge built in 1990 near Juahan. Fault appears to have cut through bridge at a skew. Precast girder superstructure thrown southward at least ten feet, knocking adjacent spans off bent caps. Compression failure of south abutment and several spans lost.
	Major cable-stayed bridge nearly completed near Mingjian. Shear cracking of bent caps, horizontal superstructure misalignments, hammering at superstructure joints, superstructure shear - compression failures, failure of a cable and severe flexural - compression spalling of pylon.
	Damage to a concrete building: soft first stories, inadequate ties, column flexural failures, column shear failures, and many joint failures. There are many cases of weak-story collapses, column failures, and joint failures.
	One of several bridges for which the fault ran beneath the bridge. The offset deformed the bridge with forces probably far exceeding those likely through inertial forces only. The piers, lightly reinforced, might be expected to have adequate strength for inertial effects, but not for deformations of the supporting earth.
	Another bridge affected by faulting. In this case a series of simple spans on piers, several spans of which collapsed. One would not be surprised to find the spans became unseated and dropped from the piers. But what projected these spans so that they ended up overhanging the supports by several meters?