Pre- and co-seismic ground deformations of the 1999 Chi-Chi, Taiwan earthquake, measured with SAR interferometry

The 1999 Mw= 7.6 Chi-Chi earthquake was the strongest inland earthquake in Taiwan in the 20th century. Five radar images acquired with the C-band SARs onboard the ERS-1/2 satellites are combined to study the pre- and co-seismic surface deformations in the epicentral area of about 1500 km2. The pre-seismic interferograms over 2-3 years show consistent fringe patterns that are equivalent to LOS displacement variations of up to about 32 mm. The deformations are likely caused by the east-west tectonic compression in the region. The short-term co-seismic interferograms show clear arc-shaped fringe patterns of about 10 fringes, equivalent to displacement variations of about 28.3 cm. The co-seismic deformation results fit well with both GPS measurements and a simulated interferogram computed based on a fault-dislocation model. This study demonstrates the capability of short-wavelength InSAR systems for monitoring ground deformations of flat terrain in tropical regions.