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 motions of the September 21, 1999, Chi‐Chi, Taiwan earthquake over the entire island are presented. For the first time, this report presents an analysis of time‐dependent spatial ground motions at both near‐source and local distances 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 modelling and greatly compliment our ability to distinguish wave generations due to sources and/or structures.