Monitoring and predicting the behavior of the Lungchuan and Chishan faults with GNSS

Taiwan sits at the boundary of the Eurasian plate and the Philippine Sea plate, which converge at a significant rate of around 8 cm/year; and as a result, this region is one of world's most unstable areas with frequent earthquakes. The use of GNSS receiver networks for monitoring ground deformation and earthquake-related geophysical events has been worldly widespread in recent years. Taiwan is no exception. In this study we will present the use of a dense geodetic network for monitoring and predicting the behavior of two major active faults in southwestern Taiwan, namely the Chishan and Lungchuan faults. The importance of this research lies on the fact that a major highway runs across the two-fault system with a viaduct and a tunnel which both have experienced rapid deformation. A dislocation model was created using the GNSS and other monitoring data collected within the network. Based on the modeling results, we predict that the relative motions of the two faults will continue to shorten the viaduct at nearly 5 cm/year and to generate uplift along the Chishan fault inside the tunnel close to 8 cm/year. We therefore suggest to completely reconstruct the highway section in this tectonically active area to avoid possible catastrophes in the future.