The excellent spatial coverage of the 21 Envisat/ASAR images (from 2003 to 2009) have been applied to monitor the activities of possible blind faults underlying the Ilan Plain,a basin located on the NE Taiwan Island that has been experienced extension.The continuous and campaign GPS stations and leveling measurements are also used to constrain the plain’s horizontal and vertical velocity field at present.They have shown a similar trend that the plain is experiencing fast subsidence and extrusion motion to the southeast.The plain’s northern and western regions are seemed to be less active than its eastern and southern parts.A triangular shaped land subsidence center (the maximum sinking rate could reach to -40 mm/yr) appears to the south of the Lanyang River based on our PS-InSAR results.Including other areas situated within/close to the cities,the land subsidence is correlated with the man-made behaviors,e.g.industrial,agricultural or urban over-usage of groundwater.Determined by the discontinuity in the PS ALOS velocity field,although weak,we could identify the possible projection trace onto the surface from the blind faults.There occurs several rate gradient with good linearity characteristics in the plain and they are in an arrangement of left-step en enchon,e.g.the Jiaoxi-Zhu’an fault,the Aijie fault,the Yilan fault,the Luotung River fault and the Dazhou fault.A series of newly recognized normal faults are also displayed by our PSI velocity discontinuity.They are shaped with the same outline as that of the Ilan Plain.After converting and comparing these multi-sourced datasets with two previous seismic reflection profiles,we further speculate that they might be produced under a book-shelf structure settings which is associated with the fast on-going opening of the Okinawa Trough to the eastern offshore.The non-axial N-S-directed right-lateral shearing stress plays an important role in controlling the tectonic process and seismic activities in the Ilan Plain.