Incorporating Change-Point Detection Updates of Frequency-Magnitude Distributions Within the Taiwan Earthquake Catalog

Kuei-Pao Chen,Yi-Ben Tsai,Wen-Yen Chang,Daniel Amorese

doi:10.3319/tao.2010.09.17.01(t)

Abstract

Threshold magnitude (M0) is an important factor in determining the magnitude of completeness in calculating seismic b values. Seismic b values can assist in determining the likelihood of earthquake events; therefore, seismic b values should be re-determined repeatedly with ever increasing precision. In this study, we use a median-based analysis of the segment slope (MBASS) to detect change points in Gutenberg-Richter frequency-magnitude distributions (FMDs) to determine M0. Results give the b value for M0-0.5 to be smaller than the b-value for M0+0.5, and the difference in b values between M0 and M0-0.5 is larger than the difference in b values between M0 and M0+0.5. Therefore, b values resulting from M0+0.5 should therefore be more accurate than b values from M0-0.5 when calculating b values using the threshold magnitude (M0). This is especially true when earthquake events are few and M0 is large such as for the time periods 1900-1935, and 1936-1972 as noted in of Taiwan's earthquake catalog.

Highlights

Since the installation of Taiwan’s first seismograph in 1897, Taiwan’s earthquake catalog has been relatively complete
The segment slope was computed for each magnitude increment based upon an analysis keyed to any magnitude value corresponding to a significant and stable change in the median of the segment slope of the frequency-magnitude distributions (FMDs)
The only important discrepancy is for the time period 1900 - 1935, in which earthquake numbers are too few to use median-based analysis of the segment slope (MBASS) effectively to determine M0

Summary

Introduction

Since the installation of Taiwan’s first seismograph in 1897, Taiwan’s earthquake catalog has been relatively complete. Changes in seismographic characteristics, network coverage, and observational practice, as well as definitional and procedural changes in magnitude determination led to inconsistent measures of earthquake magnitude. Wang (1992) reviewed in details the magnitude scales and their relationships for earthquakes in Taiwan. Chen and Tsai (2008) recompiled the different definitions of magnitude for five different time periods into a uniform standard: moment magnitude (MW) (see Fig. 1a).

Methods

Results

Conclusion