Tectonics-based shallow earthquake forecast of Taiwan Island

Frequent earthquakes have brought enormous life and property losses to Taiwan Island, and thus reliable earthquake forecasts are valuable. We form 20 tectonics-based shallow earthquake forecasts of Taiwan Island for the years 2019 and after, each with a different threshold moment magnitude, ranging from 5.45 in steps of 0.05 up to 6.40. Our results suggest that Taiwan Island may experience about 25 Mw ≥ 6.25, 40 Mw ≥ 6.00, 65 Mw ≥ 5.75 and 106 Mw ≥ 5.50 shallow earthquakes every 100 years. We demonstrate the consistency between the forecast results and the seismic catalog used for the forecasts and carry out retrospective tests against the seismic catalogs of Taiwan Island not used in the forecasts, which show higher forecast success relative to previous studies of global earthquake forecasts. We identify three gaps of Mw ≥ 6.40 shallow earthquakes, located in Yilan County, Hualien County and Taitung County. We find a general negative correlation between our Mw ≥ 6.40 shallow earthquake forecast and the population density distribution in Taiwan Island. However, we emphasize that the regions with relatively low forecast values need special attention, because these regions generally have relatively high population densities but may also experience strong earthquakes.