Geodetically observed surface displacements of the 1999 Chi-Chi, Taiwan, earthquake

The 21 September 1999 Chi-Chi, Taiwan, earthquake of magnitude M-w = 7.6 (M -L = 7.3) severely deformed the Earth's crust in the central Taiwan region. The earthquake created an 85-km-long surface rupture along the Chelungpu f ault. The epicenter was located at 23,85 degrees N, 120.81 degrees E, near the southern end of the rupture zone. Three-dimensional displacements of 28 5 geodetic control stations were determined in this study from Global Posit ioning System (GPS) observations collected before and after the earthquake. The detailed surface displacement field shows that individual stations are vertically uplifted by up to 4 m and displaced horizontally by up to 9 m, with the largest displacement occurring near the northern end of the ruptur ed thrust fault. The azimuth of the surface displacement field is approxima tely parallel to the direction of tectonic convergence of the Eurasian and Philippine Sea plates. The maximum three-dimensional displacement of 9.9 m is among the largest fault movements ever measured for modern earthquakes.