A Study of Recurrence Models of Earthquakes in Taiwan


Taiwan has one of the most complete instrumental catalogs of earthquakes in the world. Data from the Taiwan Central Weather Bureau and the Institute of Earth Sciences, Academia Sinica provide a fairly complete catalog of earthquakes with magnitude greater than 5.0 since 1900, and with magnitude greater than 3.0 since 1973. We have made a study of recurrence models of earthquakes in Taiwan using this catalog with magnitude ≥ 4.0 from 1973 to 2001 and magnitude ≥ 5.0 from 1900 to 2001. We first compared four recurrence models (i.e., exponential, Weibull, Gamma, and lognormal models) utilizing the data in fifteen circular areas of Taiwan. The model parameters were determined through data fitting by the method of moments and the method of maximum likelihood. It was found that the method of moments tends to give better fitting. Results further show that the Gamma model using the method of moments usually gives better fitting to the data than other recurrence models for all magnitudes. The two parameters (c and r) of the Gamma model are subsequently used to show the characteristics of seismicity patterns. For example, large c values appear in eastern Taiwan because of more frequent earthquakes there. Small r values are found in central Taiwan because of clustering of numerous aftershocks following the Chi-Chi earthquake. These parameters of the Gamma recurrence model are useful for estimating probabilistic seismic hazards and for forecasting the probability of future earthquakes in different areas of Taiwan. For example, the probability for a magnitude ≥ 6.0 in the whole of Taiwan reaches 70 percent at a recurrent time of about 200 days.

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