Two-dimensional reconstruction of the surface ground motions of an earthquake: the September 21, 1999, Chi-Chi, Taiwan Earthquake

The observed time history and spatial dependence of the surface ground moti ons of the September 21, 1999, Chi-Chi, Taiwan earthquake over the entire i sland are presented. For the first time, this report presents an analysis o f time-dependent spatial ground motions at both near-source and local dista nces using strong motion records. The two-dimensional ground motions of the Chi-Chi earthquake were reconstructed from more than 400 free-field strong motion records after being corrected for absolute times. The reconstructed seismic wavefields can be considered as a new type of observed data, named "3-D seismograms" here. Results of this study offer some insight into the study of earthquake source and wave propagation based on 3-D numerical mode lling and greatly compliment our ability to distinguish wave generations du e to sources and/or structures.