Seismotectonics and identification of potential seismic source zones in Taiwan

Taiwan is an active and complex tectonic region with earthquakes occurring as a response to collision between the Philippine Sea and the Eurasian plat es. Furthermore, the northward subduction of the Philippine Sea plate in no rthern Taiwan and the eastward subduction of the Eurasian plate in southern most Taiwan are significant seismogenic zones. Significant seismic hazards in Taiwan may either be induced by the plate boundary activities associated with lithospheric friction in the shallow part of the subduction zones at either end of Taiwan or by the intraplate activities due to plate collision . In the latter category, specially recognized as seismic sources for hazar d consideration are the blind thrusts in the Western Foothills and the Coas tal Plain. Similar to the 1994 Northridge earthquake, such events could be quite hazardous because the seismic sources are directly under populated ur ban areas. The subduction zone offshore of northern Taiwan is capable of pr oducing M-W>7.5 events, but much of the source zone will lie offshore. The southern subduction zone extends under the Hengchun Peninsula, but the seis micity appears to be relatively low. Also to be noted are long-term seismic ity patterns, such as the NW-trending belt of events between Miaoli and Pul l is that extends from near the surface to depths greater than 40 km. The L ongitudinal Valley faults and the Meishan fault are well known. A better un derstanding of the potential seismogenic structures such as the Longitudina l Valley fault system and Meishan fault may help us in proposing appropriat e long term measures to mitigate seismic hazards.