Kuei-Pao Chen and Yi-Ben Tsai
A catalog of Taiwan earthquakes (1900-2006) with homogenized M _w magnitudes
Bulletin of the Seismological Society of America (February 2008), 98(1):483-489

Abstract:
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 log ₁₀ N 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 _w > or =5.5 is presented (Formula 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.