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A Catalog of Taiwan Earthquakes (1900–2006) with Homogenized M_w Magnitudes

Hsin Sheng College of Medical Care and Management, No. 115, Fulin Li, Ping Cheng City 324, Tao-Yuan County, Taiwan

Yi-Ben Tsai^*

Institute of Geophysics, National Central University, 300 Jhong-Da Road, Jhong-Li City 320, Tao-Yuan County, Taiwan

^* Present address: Geosciences Department, Pacific Gas and Electric Company, 245 Market Street, San Francisco, California 94022.

Online Material: Magnitude relations and earthquake lists.

Taiwan has a relatively complete catalog of earthquakes since the first seismograph was installed in 1897. However, due to changes in seismographic characteristics, network coverage, and observational practice, the definition and procedure for magnitude determination were different during different time periods. Recognizing a complete catalog of earthquakes with consistent magnitudes is essential for delineating seismicity patterns and assessing seismic hazards for Taiwan; efforts have been made to convert the original magnitudes of earthquakes in Taiwan based on various magnitude scales to a common M_L or M_S magnitude scale. Unfortunately, the M_L or M_S magnitude scales chosen for previous studies all are subject to a fundamental limitation of saturation toward large earthquakes. Besides, these studies are nearly two decades old. In order to avoid this limitation and to follow the current trend, we have chosen in this study to convert original magnitudes of various scales to a common M_w scale. In this study we used two independent methods for magnitude conversion. In the first method we converted the original magnitudes to M_w through empirical relations between these magnitudes and M_w. This magnitude is called the old M_w. In the second method we used the best-fitting a- and b-values to convert the original magnitudes to M_w. This magnitude is called the new M_w. The converted M_w magnitudes from both methods have resulted in significant improvements over the original magnitudes and are in good agreement with each other. Nevertheless, by examining the log₁₀N versus M_w plots, we found better linearity and tighter overlap among different time periods for the new M_w than for the old M_w. Thus, we chose the new M_w as the unified magnitude for the catalog of Taiwan earthquakes. Finally, a list of 899 earthquakes from 1900 to 2006 with M_w5.5 is presented ( see the earthquake lists available in the electronic supplement to this article). The list is considered complete for the whole period from 1900 to 2006.