Evaluation of earthquake potential and surface deformation by Differential Interferometry

Uncertainties in the length of active faults and the styles of deformation often hamper the evaluation of seismic potentials in a region. In the area near Chiayi City of southwestern Taiwan, where historically there have been many strong earthquakes, complex fault and fold systems produced by regional tectonic forces and the subsequent deformation are frequently obscured by vegetation and anthropogenic effects; and therefore detailed deformation information has not been available for evaluation of the seismic potential. By stacking the results from Differential Interferometry and removing the ambiguity of interferograms using GPS data, we were able to retrieve surface deformation information about the area under consideration near Chiayi City. In our results, we found that the Meishan fault to the north of Chiayi City extended 10 km to the west of its currently documented area and served as a geological boundary separating the northern part, where sediments were thicker, from the southern part of the westward extension of the Meishan fault. Chiayi City was under active deformation by a double plunging fold with vertical uplift rate at approximately 1 cm/yr. Frequent seismicity and active deformation allowed the tectonic stress to permute between strike–slip and thrust in this area. Continuous folding of Chiayi City and episodic large earthquakes along the Meishan Fault posed a serious threat of seismic hazards in this region, and called for continuous monitoring of the area.