Foreshock characteristics in Taiwan: Potential earthquake warning

Although foreshocks are often considered as a potential precursor in the short-term earthquake prediction, how to identify foreshocks before the mainshock occurred is a problem. Abundant earthquakes in the Taiwan area might provide a good opportunity for investigating general foreshock characteristic as well as the potential earthquake warning. Here 10 earthquake sequences with significantly felt foreshocks (ML ≧≧ 4.0) are identified from an examination of 161 earthquakes (ML ≧≧ 5.0) in the Taiwan area during the period between 1990 and 2004. In addition to addressing larger magnitudes (ML ≧≧ 4.0), the criteria for selecting foreshocks have considered that (1) the earthquakes occurred within a distance of 15 km and 5 days to the main shock and (2) focal mechanisms of the main shock and foreshocks were generally consistent. The results show felt foreshocks often occurred at the strongly heterogeneous crust, particularly along the convergent zone between the Eurasian and Philippine Sea plates. Besides, the absence of clustered earthquakes after some large foreshocks may be considered as a criterion to distinguish felt foreshocks from the main shock for improving our ability of earthquake warnings in the Taiwan area.