Study group for the 921 Taiwan Earthquake,
Disaster Prevention Research Institute, Kyoto University
2. Surface Faulting
There was about 60 km of surface faulting on a north-south trending Chelongpu fault. At the northern end the faulting turned toward the east-northeast. On the north-south section of the fault there was generally 1 - 4 meters of vertical displacement on a shallow angle thrust. On the east-northeast trending section there was 4 to 8 meters of vertical displacement and 1 - 9 meters of lateral displacement. The vertical displacements are in the class of the largest surface fault movements observed for earthquakes worldwide.
3. Earthquake Damage
For the whole area, there was more damage observed on the hanging wall of the reverse fault. There was more widespread damage to buildings in the southern part of the rupture area, especially to smaller buildings. In the northern region the damage was more concentrated very close to the surface fault in a zone 10 to 100 meters wide.
4. Aftershocks
There is a strong aftershock sequence that is continuing to occur. As of September 27, there have been 6 large (>M6.0) aftershocks. Many of the aftershocks may be triggered events off the main fault.
5. Rapid Earthquake Information and Strong-Motion
The CWB automatic earthquake information system performed well and determined the magnitude, location, and intensity distribution in about 100 sec. Essential information was reported to emergency centers of the national and provincial governments and staff of the CWB within 120 sec. Of the 1000 strong-motions instruments deployed in the country, data from 40 stations near the earthquake have been collected. Maximum accelerations were 200 to 900 gals.
Acknowledgements
This study would not have been possible without the help of Prof. Chyi-Tyi Lee, Institute of Applied Geology, National Central University and Prof. Kuo-Fong Ma, Institute of Geophysics, National Central University. We also thank Prof. Yi-Ben Tsai and Prof. Wong at the National Central University and Dr. Win-Bin Cheng, Dr. Yih-Min Wu, and Dr. Wu at the Seismology Center of the Central Weather Bureau.