Spatial distribution and age dependence of human-fatality rates from the Chi-Chi, Taiwan, earthquake of 21 September 1999

The 1999 Chi-Chi, Taiwan, earthquake caused many fatalities and much econom ic loss for people living in the central part of the island. It also provid ed many valuable lessons for mitigating future earthquake loss. In this art icle we have analyzed the human-fatality data from the earthquake in terms of spatial distribution and age dependence to reach the following conclusio ns. First, rupturing of the Chelungpu fault definitively influenced the spa tial distribution of fatalities. Ground ruptures caused by unusually large thrust and left-lateral displacement of the east-dipping fault resulted in almost total destruction of structures on the hanging-wall block along the 100-km-long fault zone. Patterns of damaging ground motion were highly asym metric about the fault trace. High ground accelerations above 400 gal resul ted in high fatality rates up to 1.112% in the sparsely populated rural are as east of the fault. Fortunately, the densely populated urban areas west o f the fault suffered substantially lower fatality rates below 0.002% due to low ground accelerations significantly below 400 gal. Secondly, clear age dependence of the human-fatality rate was found from demographic data of th e two hardest-hit Nantou and Taichung counties. Results for both counties d efine almost identical functions that shows people older than age 40 are in creasingly more vulnerable with increasing age to life loss in earthquakes. These two conclusions can be applied to make a reliable estimation of the total human fatalities in areas of high seismic intensity either before a l arge earthquake by performing scenario studies, or shortly after a real ear thquake by a system of rapid intensity mapping. Finally, empirical time fun ctions of the cumulative numbers of people found killed, injured, and missi ng during the first hours following the Kobe, Japan, and Chi-Chi, Taiwan, e arthquakes both show that search and rescue operations were critical in the first 48 hr.