Impact of a large earthquake on a GPS network: The case of the 1999 Chi-Chi, Taiwan earthquake

Abstract

On 20 September 1999, Taiwan was hit by the largest inland earthquake (M-w = 7.6) in the last century resulting in an 80-kilometre thrust rupture almost directly along the existing Chelungpu fault. Here, we estimated the coordinates of the GPS stations by using the annual epoch-observed and permanent continuously-recorded GPS data covering the 1992-1999 period Taking into account the effects of secular motion and post-deformation, we calculated the corrected coseismic displacements. Relatively large coseismic displacements of 8-9 in in the horizontal and vertical components were found in the northern part of the fault. Stations on the hanging wall shifted horizonatly 2-9 in in the NW direction and decreased in magnitude from west to east. On the other hand, displacements on the footwall were less than 2 in in the SE direction hid increased from west to east. The size of the zone overlapping the hanging wall and the foowall showed a decrease of 796 ppm in 494 km(2). This is in direct contrast to areas near the fault which increased in size from 13 to 23 7 ppm. Significant postseismic deformations were also observed in data from the existing 44 permanent stations and 7 temporary stations. Additionally, large postseismic deformations of 10-20 cm were found at stations SUAM, 100 7 and YUSN within 10 months.