Download Advances in Earthquake Precursor Studies in Taiwan

Advances in Earthquake Precursor Studies in Taiwan
Yi-Ben Tsai1, Horng-Yuan Yen1, and Jann-Yenq Liu2
1. Department of Earth Sciences and 2. Institute of Space Science
National Central University
ABSTRACT
Taiwan provides a promising natural laboratory for earthquake precursor studies,
owing to its highly active seismotectonic environment. Frequent destructive
earthquakes occurred on land near densely populated areas further make identification
of earthquake precursors a worthy research topic. Recognizing this unique
combination of favorable natural conditions for scientific advancement and potential
societal benefits on disaster reduction, Taiwan scientists have undertaken a series of
multi-year multidisciplinary research projects on earthquake precursors since early
1980s. In this paper we will highlight significant advances made by these studies, as
well as venture on future prospect. The first project on earthquake precursor studies in
Taiwan started in 1979. Under this project, spatial and temporal changes in
microearthquake activities over all Taiwan were analyzed using the data obtained by
the Taiwan Telemetered Seismographic Network (TTSN). Meanwhile, repeated
measurements of gravity, geomagnetic total intensity, crustal deformation and radon
content in hot springs were made at selected locations to monitor their temporal
changes and to study possible correlation with seismic activities. Although no
significant earthquake precursors were found during the five-year project, some of the
instruments, such as the gravimeters and magnetometers, were used in the following
years to produce the gravity and geomagnetic anomaly maps of Taiwan. The expertise
gained from electronic trilateration surveys was transitioned to GPS methodology
seamlessly. Most significantly, the geomagnetic observation network provided records
showing definitive precursors preceding the 1999 M7.6 Chi-Chi earthquake and the
following M6.4 Chia-Yi earthquake. These observations rekindled interest of many
scientists in Taiwan to search for other precursors of the Chi-Chi earthquake, funded
by the National Science Council and Ministry of Education. Since then, changes in
seismicity, P wave velocity, groundwater level, ground surface deformation, and
ionosphere electron content have been identified with precursory time ranging from a
few days up to five years. Notably, these findings have prompted several government
agencies, such as the Central Weather Bureau, the Central Geological Survey and the
Water Resource Agency to install and operate networks of real-time continuous GPS,
geomagnetic stations, groundwater wells, borehole strain meters, and geochemical
stations, in addition to the dense short-period and broadband seismic networks.
Recent moderate earthquakes are beginning to show good potential for these networks
to catch more earthquake precursors in the future.