Estimates of earthquake recurrences in the Chiayi–Tainan area, Taiwan

In the light of the important role played by the return period in seismic hazard analysis, two types of statistical analyses (Gutenburg–Richterʹs law and Markov chain) were applied to study the earthquake periodicity in the Chiayi–Tainan area. There are two data sets prepared for this study; one contains earthquakes with ML≥4 (283 events) during the 1900–1995 period, the other contains earthquakes with ML≥2 (3816 events) during the 1973–1995 period. The mean return period and b values estimated with Gutenburg–Richter relation for earthquakes in the study area are in agreement with previous studies. The mean return period for ML≥6 earthquakes is 9.7 years from the data in 1900–1995 period, and 17 years from the data in 1900–1995 period. rkov chain measures the transition characteristics of earthquakes, and estimates that ML=6–6.9 and ML≥7.0 earthquakes repeat at intervals of 28 and 135 of ML≥4 earthquake events, respectively, in the Chiayi–Tainan area. This study also demonstrated that investigation of “substitutability” phenomenon is applicable to earthquake data, which suggests high similarity for low-magnitude earthquakes and dissimilarity for high-magnitude earthquakes. The result from these statistical approaches for earthquake occurrences leads to a conceptual model inferring fault behavior. This model is supported by the recent geologic findings, which may be potentially useful in earthquake hazard assessment.