Determining the surface deformation in ilan plain using PSI technique

The Ilan plain in the northeastern Taiwan is generated by the southwestward extension of the Okinawa Trough. This plain is filled by alluvial material and is almost equilateral triangular in shape and moderately tilted to the east. Different opinions about the formation of this plain and its relationship to the Okinawa Trough have been proposed in the last few decades. In this paper we analyzed the present-day surface deformation of the Ilan plain and try to find the relationship with the regional tectonics. Our approach is mainly based on consideration of displacement revealed by Persistent Scatterers InSAR (PSI), totally 23 Envisat images acquired by ESA and observed temporally-variable processes of Ilan plain between 2004 to 2008 have been used. Our preliminary results show a relative subsidence in Ilan city, Lanyansi and Loudung city, and a slight uplift in the Hsuehshan and Backbone Ranges. This result is coincided with the previous local leveling measurement. According to the characteristics of GPS velocity field and fault distribution we have decided to Ilan Plain is divided into three areas which are Zone I, Zone II and Zone III. From Zone I the average GPS velocity is 2 mm/yr direction to northeast and Zone II is 4 mm/yr direction to northeast. However, the maximum GPS velocity is in the Zone III, which is 14 mm/yr direction to southeast. The Zone III with a completely different direction for the other two areas. To sum up, the most active area located in the southern part of the Ilan plain.