- © 2015 by the Seismological Society of America
Taiwan has been constantly threatened by large, damaging earthquakes as the tectonic consequence of persistent collisions between the Philippine Sea plate and Eurasian plate. Use of an earthquake early warning (EEW) system is one of the effective tools for seismic-hazard mitigation and has operated in many countries, including Japan, Taiwan, Mexico, and the United States (e.g., southern California) (Kanamori et al., 1997; Allen et al., 2009; Lee and Wu, 2009; Satriano et al., 2011). Taiwan initiated the development of EEW after the Hualien offshore earthquake (Mw 7.8) occurred on 15 November 1986. This earthquake caused large losses of life and property due to basin amplification in the metropolitan Taipei area, with an epicentral distance of 120 km. A timely warning can be announced to the highly populated Taipei city if an EEW system in the Hualien area can provide the earthquake information within 20 s (i.e., travel time of crustal shear wave over a distance of 120 km).
There are two types of EEW system: (1) the front-type warning, which collects the seismic records close to the epicenter and dispatches the earthquake warning to a more-distant area, has higher accuracy than the onsite one because of the use of more stations and longer time window; (2) the onsite-type warning has a smaller reporting time but lower accuracy because it relies on only one or a few stations.
The backbone of the present Taiwan EEW system is the Rapid Earthquake Information Release System (Wu et al., 1997, 2000) operated by a government agency, the Central Weather Bureau (CWB), since 1995. This system, consisting of 109 telemetered seismic stations, is operated in the front-type warning mode. This system can provide earthquake information mostly within 20 s following an earthquake occurrence (Wu and Teng, 2002; Hsiao et al., 2009, 2010).