Multidisciplinary Earthquake Precursor Studies in Taiwan: A Review and Future Prospects

Taiwan is situated in a unique plate‐tectonic environment. It is intensely compressed by the Philippine Sea plate on its east side and by the Eurasian plate on its west. These active tectonic processes have resulted in a collision zone encompassing the main part of Taiwan, which lies between two subduction zones: one in its northeastern offshore region, and another in its southern offshore region. Frequent shallow earthquakes take place inland, with many disastrous ones striking the densely populated areas in western Taiwan, as well as the Longitudinal Valley in eastern Taiwan. The Taiwan earthquake science community recognized early on the significance of these seismotectonic and societal impacts, launching the first multidisciplinary earthquake prediction research program in late 1970s, as a cooperative effort between the Institute of Earth Sciences (IES) and the University of Southern California (USC), jointly funded by the National Science Council and the US Geological Survey. The program comprised seismological, geodetic, gravitational, geomagnetic, and geochemical components. After the 1999 M 7.6 Chi‐Chi earthquake, a new series of multidisciplinary research programs focused on the integrated study of Taiwan earthquake precursors, code named iSTEP‐1, iSTEP‐2 and iSTEP‐3, were launched. These programs included the earlier components, as well as adding a seismo‐electromagnetic component and statistical validation methodology. These programs are described in the first section. At least seven different types of precursors have been positively identified to be associated with the Chi‐Chi earthquake under the above‐mentioned programs, as well as by other researchers. These precursors include seismicity, crustal deformation, groundwater level, geomag-netic, atmospheric, and ionospheric changes, with premonitory times ranging from years, months, down to days. Among them, the ionospheric and electromagnetic precursors appear to be most promising. These findings are summarized in the second section. Finally, we present our prospects for future multidisciplinary earthquake precursor studies in Taiwan. In consideration of the seismotectonic and societal impacts, several island‐wide advanced monitoring networks have been installed and operated by dedicated technical staff and researchers. In light of the positive findings from the Chi‐Chi earthquake, Taiwan arguably could be considered as a highly promising multidisciplinary test ground for earthquake precursors. It is hoped that the earthquake science com-munity, through persistent and diligent work, would be successful in identifying positive precursors in years, months and/or days to benefit people in Taiwan prior to future disastrous earthquakes. In the long term, sufficient empirical precursors observed in Taiwan may help to unravel a fundamental question in earthquake science: “Are there earthquake precursors that can lead to useful predictions?”.