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Relationship Between Building Damages and Indices of Seismic Ground Motion Based on Strong Motion Records from the September 21, 1999, Chi-Chi, Taiwan, Earthquake

by Jun'ichi Miyakoshi, Masafumi Mori, Hiroshi Kambara and Yasuhiro Hayashi

A major earthquake (M_w=7.6) occurred near the town of Chi-Chi in Nantou county, central Taiwan, on September 21, 1999. We investigated the building damages around the earthquake observation stations. The strong motion recordings from over 400 stations in this earthquake area were pre-published by Central Weather Bureau of Taiwan on December, 1999. In this paper, we examined the relationships between building damages and four indices of seismic ground motions, which were peak ground acceleration (PGA), peak ground velocity (PGV), spectrum intensity (SI) by Housner (1965), and seismic intensity of Japan Meteorological Agency (I_JMA). In this result, we have shown the following features: (1) We pointed out that most of the damaged school buildings were not very tough, since most of the damages surpassing the minor ones in the investigated areas were all severe. (2) The correlation coefficient of PGA to PGV in the investigated areas was very low. Only a few buildings were damaged severely in the areas that PGA/PGV were less than about 3. (3) In the areas where PGA, PGV, and I_JMA were less than 400 cm/s/s, 50 cm/s and 5.5, respectively, only a few buildings were severely damaged. (4) In those cases where some indices are modified by filtering or where the selected PGA/PGV values fell in a determined area, it was shown that buildings damages could be explained to some extent by looking at the indices of seismic ground motions.