A Preliminary Report on the 1999 Chi-Chi (Taiwan) Earthquake

Abstract

A major earthquake ( M 2 =7.6) occurred near the town of Chi-Chi in Nantou county, central Taiwan, at 1:47 a.m., 21 September 1999, local time (UTC is 17:47, 20 September 1999), about 150 km south of Taipei. As of 13 October 1999 Taiwan's Interior Department record shows that the death toll is 2,333 and 10,002 people were injured. Thousands of houses collapsed, making more than 100,000 people homeless. This disastrous earthquake provided a wealth of modern digital data for seismology and earthquake engineering because an extensive six-year seismic instrumentation program for Taiwan was successfully implemented three years ago by the Central Weather Bureau (CWB). This program was guided by the CWB Advisory Committee and benefited from cooperative projects with the U. S. Geological Survey and the Southern California Earthquake Center. The Seismology Center of CWB has the official responsibility of monitoring earthquakes in and near Taiwan. An extensive seismic instrumentation program, especially for the urban areas of Taiwan, with mostly strong-motion instruments was completed in 1996. At present, the following instruments are in operation: 1. a real-time digitally telemetered seismic network of 80 three-component, short-period stations, 2. a rapid earthquake information release system based on 61 real-time telemetered digital accelerographs (also record on site in trigger mode), 3. about 650 modern digital accelerograhs in free-field sites (all record in trigger mode; 61 sites are also continuously telemetered to CWB Headquarters in Taipei for 2 above; and some sites have more than one accelerograph), and 4. 56 real-time strong-motion arrays (up to 60 uniaxial accelerometers in each array and include one 3-component accelerometer outside the structure whenever possible) in buildings and bridges. Taiwan is a small island of about 35,000 square kilometers (about 9% of the area of California or Japan). More than half of the area of Taiwan is the high central mountain …