PRELIMINARY RESULT OF SURFACE DEFORMATION IN SUBURBAN CENTRAL TAIWAN OBSERVED BY PSINSAR

The convergence between the Philippine Sea plate and the Eurasian continent had created one of the most active tectonic regimes in the island of Taiwan. The net convergence rate between the Philippine Sea plate and the Eurasian plate is about 8.2 cm/yr along 307° azimuth and the shortening caused by the convergence between the two plates were partitioned across the entire island, which can be reflected by the rugged landscape that are approximately perpendicular to the convergence direction of the two plates. Significant amount of these deformation occurred in the western foreland where the population density is high. In addition to the tectonic-related deformation, anthropogenic activities such as groundwater extraction would also induce surface deformation. This type of surface deformation tends to affect areas with high population density as well. In order to quantify different types of deformation and further mitigate the hazards caused by both tectonic and anthropogenic activities, many geodetic measurements were deployed in Taiwan. However, the spatial density of these geodetic measurements were generally very low due to the high cost of the instrument or the time required for the campaign. An alternative method was using SAR interferometry, however, the vegetations and farmland in central Taiwan prevent the radar signal from having high enough coherence to form meaningful interferogram. Persistent scatterer InSAR was therefore deployed in our study area to acquire the deformation signal. The result showed that a significant amount of area in central Taiwan was subjected to a very rapid subsidence rate of up to 10 cm/yr. Precise leveling in this area also provided evidence for such a rapid subsidence in this area. Further works are needed in order to precisely map out the area affected and find out the causes of the phenomenon.