Ground displacements in the meizoseismal area of the September 20, 1999, Chi-chi earthquake are derived from accelerograms at 39 stations. On the hanging wall side a maximum horizontal, NW-directed motion of 8 meters and a vertical rise of 3.7 meters are found near the northern end of the N-S trending surface trace of the fault. On the footwall side and next to the fault a maximum horizontal motion of 1.3 meters and a maximum downward vertical motion of 1 meter are observed. The displacement field describes the source as a thrust fault with left-lateral motion. The displacements increase from south to north along the fault, and so does the left-lateral component of the fault motion, from about 10% to 60% of the total horizontal displacement. The recorded motions, especially ground velocities and accelerations, are noticeably stronger on the hanging wall side than on the footwall side. ¿ 2001 American Geophysical Union