| Summary: | 碩士 === 國立臺灣大學 === 地質科學研究所 === 94 === I apply the D-InSAR technique to monitor the active crustal deformation both in Tainan and Central Taiwan by using ERS SAR images during 1996-2000 (Tainan) and 1999-2000 (Central Taiwan). The Mw 7.6 Chi-Chi earthquake occurred on 21th September, 1999 in central Taiwan and a ~100 km surface rupture along the Chelungpu fault was observed. I apply InSAR technique to measure the coseismic and postseismic deformation in the footwall and hanging wall of the Chelungpu fault. The 2-pass method is used to obtain interferograms from DEM data and 5 ERS-1/2 SAR images passing central Taiwan between February 1999 and August 2000. The result of D-InSAR (Differential-InSAR) reveals the significant coseismic deformation on the footwall area of the Chelungpu fault along the line of sight (LOS) of ERS satellites. The coseismic slant range displacement (SRD) on the footwall of the Chelungpu fault demonstrates a difference of 32.6 cm from the coastal area to the west side of the Chelungpu fault. This observation shows the maximum coseismic uplift is close to the west side of the fault. The postseismic interferogram shows no significant postseismic slip on the footwall of the Chelungpu fault, however a SRD of ~20 cm is observed on Shinshou tableland located on the hanging wall. Besides, a SRD of ~10 cm is also observed along the E-W reverbanks of the Choshui river. A significant land subsidence area was with total subsidence ~10 to 20 mm during a period of one or two months detected near the Changhua County both in coseismic and postseismic InSAR pairs. In addition, we recalculate the coseismic deformation revealed by GPS observations on the footwall of Chelungpu fault into the SRD in order to compare with the deformation pattern of D-InSAR. I also try to exploit 3-D dislocation models to estimate movement of the fault plane modified from a ramp-décollement model suggested by Johnson et al. (2004). Thus the coseismic deformation inferred from this dislocation model can be transferred into the coordinate of the SRD. The results of the simulated intergerograms show the same trend as those from D-InSAR. However, low coherence of SAR interferograms in the southern part of the study area in Chunghua County limits the accurate comparison with the predicted models.
The Tainan tableland is located in-between a blind fault in the west and the Houchiali Fault in the east, thus the Tainan tableland can be interpreted as a pop-up structure in a fold-thrust belt at active tectonic margin. Interferometric processing of six SAR images reveals the average SRD as ~12.5 mm/yr, and it increases from west edge of Tainan tableland and decreases across the Houchiali fault. The campaign-mode GPS data set from 1999 to 2003 indicate an average horizontal movement of 12±4 mm/yr in the direction of N44°W for the Tainan tableland with respect to western coastline. Furthermore 5 times precise leveling surveys across Tainan tableland over a period of 2 years show an uplift rate of ~14 mm/yr for the benchmarks on the tableland. The horizontal strain rates calculated by GPS horizontal data showed the extensional on the Tainan tableland with the rate of ~6 μstrain/yr and compressional regime on the coast line and the eastern Tawan lowland with the rate of 5 μstrain/yr. By combining with the horizontal velocity of GPS data and the SRD of D-InSAR we transfer the SRD into vertical deformation and discuss the deformation pattern and seismic hazards of Tainan area.
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