Estimated Seismic Intensity Distributions for Earthquakes in Taiwan from 1900 to 2008

Abstract

In this study we recreated peak ground accelerations (PGA) and peak ground velocity (PGV) distributions for Taiwan by applying the attenuation relations of Liu and Tsai (2005) to calculate the PGA and PGV values for 1989 Mw ≥5:0 earthquakes in a catalog of earthquakes from 1900 to 2008 with homogenized magnitude (Mw )( Chen and Tsai, 2008). We further combined the PGA and PGV values to obtain corresponding modified Mercalli intensity (MMI) values (Wald, Quitoriano, Heaton, Kanamori, et al., 1999) and their spatial distributions and recurrence intervals. We adopted a logarithmic functional form analogous to the Gutenberg-Richter relation for seismicity to represent the annual frequency of seismic intensity parameters: log10N a blog10PGA, log10N a blog10PGV, and log10N a bI. The regions with high PGA and PGV values are often associated with low b values in these equations. As it is well known that the Mw 7.45 Chi-Chi earthquake of 21 September 1999 had produced high PGA values (in excess of 0:9g) and PGV values (in excess of 300 cm=s), we used these relations to estimate the Poisson probability distributions in Taiwan for MMI ≥ VIII (i.e., PGA ≥ 485g) for recurrence intervals of 30, 50, and 100 years. The results show a wide range of differences in the Poisson probability of MMI ≥ VIII among different areas of Taiwan. For example, for a 50-year interval, this probability at 10 major cities in Taiwan is as follows: Taipei 0.67%, Hsinchu 2.15%, Taichung 5.24%, Chiayi 24.35%, Tainan 1.61%, Kaohsiung 0.04%, Hengchun 4.94%, Ilan 17.67%, Hualien 37.04%, and Taitung 9.82%. These esti- mates should be of interest to city planners, especially for earthquake preparedness planning.