Three-dimensional deformation along the rupture trace of the September 21st, 1999, Taiwan earthquake: a case study in the Kuangfu school

In Central Taiwan, the destructive Chichi earthquake (Mw=7.6) of September 21st, 1999, produced a nearly 100-km-long rupture trace following the Chelungpu Fault. This paper shows how the geometry of the fault slip can locally be determined in three dimensions, based on analyses of earthquake fault in the Kuangfu stadium. The fault at this site is reverse and left-lateral. The three-dimensional geometrical analysis, done with a variety of data through independent determination modes, all applied to the deformation of the surface layer of the stadium tracks, allows complete verification of the results. Not only do these analyses constrain the fault behaviour in terms of trend, dip angle, obliquity and amount of slip, but also they reveal variations in both the horizontal and the vertical fault geometry. The comparison with relative displacements recorded at larger distances from the fault reveals that slip partitioning occurs, with nearly dip-slip thrusting along the rupture trace and distributed left-lateral shear in a deformed zone of the hanging wall, adjacent to the main fault.