Aspects of Large Earthquakes in Taiwan

Large earthquakes (Ms ≥ 7) cause severe damage across vast areas, extending for tens to hundreds of kilometers. Despite their lower frequency compared to smaller events, it is important to characterize them due to their devastating effect. For forty‑nine Ms ≥ 7 earthquakes from 1906 to 2024 in the Taiwan region, the moment magnitude, Mw, is smaller than Ms. The whole region is divided into six seismic zones based on regional tectonics. The spatial distribution of epicenters shows that most of the events occurred in the zone near the eastern costal line and offshore eastern Taiwan and only a few inland events happened on two zones in western Taiwan. The time series of earthquakes in six seismic zones show irregular recurrence behavior with aperiodicity. For the whole region, the time series may be separated into three intervals. The average inter-occurrence time between two sequent events in a time interval increases from the first time interval to the third one: 404.24 days (1.11 years), 845.30 days (2.32 years), and 2369.88 days (6.49 years), respectively, for the first, second, and the third time intervals. The average inter-occurrence time from for the whole time period is 895.7 days (2.45 years). The existence of a weak memory effect in the time series might be due to the presence of local stress transfer for some groups of events. The earthquake occurrences are the most active in April, September, and December, and the least active in May and August. The difference in seismic activities between the local daytime and local night-time is small, thus indicating small effects on generation of large earthquakes caused by solar and lunar tides.