Abstract：The distribution of near-fault strong ground motion during Chi-Chi earthquake (Mw7.6) has two remarkable characters：(1) the distribution of horizontal peak acceleration，peak velocity and displacement along the fault is asymmetric and the effect of hanging-wall is distinct；(2) the distribution of acceleration，velocity and displacement are inconsistent. Based on theoretical analysis of focal mechanism and research on medium rigidity of fault，a model of finite source of Chi-Chi earthquake is established；and then the ground motion of the model is simulated. The distribution characteristics of simulation is similar to that of ground motion monitored by instruments. Without considering the site condition，the rigidity of fault surface affects acceleration and velocity value of near-site strong ground motion to some extent，the peak ground acceleration and velocity are respectively in proportional to media rigidity — and . Furthermore，the parameters of focal mechanism，such as dislocation，obliquity，rupture mode，have remarkable influence on distribution of strong ground motion. The uneven distribution of strong ground motion near the source is attributed to the complexity of source by former researchers. But our studies result in a farther conclusion，that the mechanism and rigidity of fault surface are the main factors resulting in uneven distribution of strong ground motion near the source，and the complexity of source has relationship with the mechanism and rigidity of fault surface.
