Three-dimensional patterns of seismic deformation in the Taiwan region with special implication from the 1999 Chi-Chi earthquake sequence

We compile a comprehensive list of hypocentral locations and source parameters for earthquakes occurred in the Taiwan region. The collected database is used to construct 3D patterns of seismic deformation that are associated with various tectonic processes such as subduction and collision between the Philippine Sea plate and Eurasia. Specifically, we divide the entire Taiwan region into a 3D grid of 10km interval and the amount of seismic moment released at each point is the sum of all individual events in the vicinity. In case when the physical dimension of an earthquake is larger than 10km, the corresponding seismic moment is distributed across multiple grid points. This quantitative approach gives a better depiction on many first-order features in the region. The most intriguing one is that a significant deficit in the total amount of released seismic moment can be clearly identified around the Chi-Chi source region before the big earthquake occurred in 1999. The deficit trough is then filled by the seismic moment of the Chi-Chi earthquake sequence. This deficit-then-fill pattern in a region's seismic moment distribution can be used as an indicator to pinpoint the locations of large earthquakes in the foreseeable future. Following this argument, we suggest that disastrous earthquakes with magnitudes comparable to that of the Chi-Chi earthquake are due for the two regions adjacent to the Chi-Chi source area (i.e., the Miaoli-Hsinchu domain to the north and the Chiayi domain to the south).