Finite-Source Modeling of the 1999 Taiwan (Chi-Chi) Earthquake Derived from a Dense Strong-Motion Network

UTC) (located at 23.853 � N, 120.816 � E, and depth of 7.5 km) inflicted severe regional scale damage to Taiwan. The strong-motion wavefield was captured by a dense network of stations (with average station spacing of 5 km), which represents the most complete strong-motion dataset to date to use to study the kinematic source process of an earthquake. We inverted velocity waveforms recorded by 21 stations for the spatial variation in slip on a planar fault model composed of 416 subfaults, each with a dimension of 3.5 km by 3.5 km. The planar model has a strike of N5 � E and a dip of 30 � E, and the inversion solves for the direction and magnitude of the slip. To account for possible temporal source complexity we allowed each subfault to slip within 10 overlapping time windows, each with a duration of 3 sec. The results show that the source is composed primarily of three major asperities, the first of which is mainly dip slip, extending from the hypocenter to the northern end of the surface rupture. In this asperity, slip occurred in two pulses separated in time by 5 sec. The dislocation rise time for each pulse is short (3–4 sec), yielding an approximate average slip velocity of 80 cm/sec. The second asperity is located at shallow depth near