Preliminary results of the iSTEP program on integrated search for Taiwan earthquake precursors

Abstract

The predictability of earthquakes has been a hotly debated question in earthquake science for some time. The answer to which begs another question, "Are there credible earthquake precursors?" Intrigued by these questions and encouraged by instrumental observations of conspicuous ionospheric and geomagnetic disturbances before the disastrous 1999 Chi-Chi earthquake, we decided to undertake an integrated Search for Taiwan Earthquake Precursors, called the iSTEP program. The multidisciplinary program includes five major components aimed at identifying potential seismological, geomagnetic, geodetic and ionospheric precursors, and statistical testing of any identified precursors. Since the program's inception in April 2002, some encouraging preliminary results have been obtained. These includes precursory P wave travel-time changes six years before the Chi-Chi earthquake, identifiable geomagnetic changes two years before M ≥ 6 earthquakes, consistent ionospheric anomalies three days before M ≥ 5 earthquakes. We have also developed high-resolution radar interferometric methods for monitoring crustal deformation. A method for forecasting aftershock distribution on the basis of stress transfer has also been successfully tested on the Chi-Chi earthquake sequence. Aided by the newly installed geomagnetic and ionospheric networks we are hopeful about identifying more earthquake precursors and developing relevant physical mechanisms in the remaining two years of the iSTEP program.