Two-dimensional Co-Seismic Surface Displacements Field of the Chi-Chi Earthquake Inferred from SAR Image Matching
نویسندگان
چکیده
The Mw=7.6 Chi-Chi earthquake in Taiwan occurred in 1999 over the Chelungpu fault and caused a great surface rupture and severe damage. Differential Synthetic Aperture Radar Interferometry (DInSAR) has been applied previously to study the co-seismic ground displacements. There have however been significant limitations in the studies. First, only one-dimensional displacements along the Line-of-Sight (LOS) direction have been measured. The large horizontal displacements along the Chelungpu fault are largely missing from the measurements as the fault is nearly perpendicular to the LOS direction. Second, due to severe signal decorrelation on the hangling wall of the fault, the displacements in that area are un-measurable by differential InSAR method. We estimate the co-seismic displacements in both the azimuth and range directions with the method of SAR amplitude image matching. GPS observations at the 10 GPS stations are used to correct for the orbital ramp in the amplitude matching and to create the two-dimensional (2D) co-seismic surface displacements field using the descending ERS-2 SAR image pair. The results show that the co-seismic displacements range from about -2.0 m to 0.7 m in the azimuth direction (with the positive direction pointing to the flight direction), with the footwall side of the fault moving mainly southwards and the hanging wall side northwards. The displacements in the LOS direction range from about -0.5 m to 1.0 m, with the largest displacement occuring in the northeastern part of the hanging wall (the positive direction points to the satellite from ground). Comparing the results from amplitude matching with those from DInSAR, we can see that while only a very small fraction of the LOS displacement has been recovered by the DInSAR mehtod, the azimuth displacements cannot be well detected with the DInSAR measurements as they are almost perpendicular to the LOS. Therefore, the amplitude matching method is obviously more advantageous than the DInSAR in studying the Chi-Chi earthquake. Another advantage of the method is that the displacement in the hanging wall of the fault that is un-measurable with DInSAR due to severe signal decorrelation can almost completely retrieved in this research. This makes the whole co-seismic displacements field clearly visible and the location of the rupture identifiable. Using displacements measured at 15 independent GPS stations for validation, we found that the RMS values of the differences between the two types of results were 6.9 cm and 5.7 cm respectively in the azimuth and the range directions.
منابع مشابه
Horizontal coseismic deformation of the 1999 Chi-Chi earthquake measured from SPOT satellite images: Implications for the seismic cycle along the western foothills of central Taiwan
[1] The 1999 Chi-Chi earthquake, Mw = 7.6, broke a major thrust fault along the western foothills of the Central Range of Taiwan. We have measured the horizontal coseismic displacement field by correlating optical satellite images acquired before and after the earthquake. These data reveal the fault trace and a clockwise rotation of surface displacements toward the north with much larger displa...
متن کاملObservations of changes in waveform character induced by the 1999 Mw7.6 Chi-Chi earthquake
[1] We observe changes in the waveforms of repeating earthquakes in eastern Taiwan following the 1999 Mw7.6 Chi-Chi earthquake, while their recurrence intervals appear to be unaffected. There is a clear reduction in waveform similarity and velocity changes indicated by delayed phases at the time of the Chi-Chi event. These changes are limited to stations in and paths that cross the 70 × 100 km ...
متن کاملFinite fault inversion of the September 25, 1999 (Mw = 6.4) Taiwan earthquake: Implications for GPS displacements of Chi-Chi, Taiwan earthquake sequence
[1] The September 25, 1999 Chi-Chi Taiwan aftershock (Mw=6.4) occurred on a down dip extension of the fault ruptured in the mainshock. Strong motion data were used to invert for the finite-source process and test for the causative fault plane. We performed a grid-search over a range of focal mechanisms and found a preferred model (strike=5 , dip=30 , slip=100 ) different from teleseismic studie...
متن کاملEvidence of fluid - filled upper crust from observations of post - seismic deformation due to the 1992 M w 7 . 3 Landers earthquake
I investigate post-seismic deformation due to the 1992 Mw7.3 Landers, southern California, earthquake using the entire catalog of the ERS Synthetic Aperture Radar (SAR) data, and GPS measurements made between 1992 and 1999. The stacked interferometric SAR data spanning the time period of seven years between the Landers and the Hector Mine earthquakes reveal a transient post-seismic deformation ...
متن کاملMapping surface deformation related to the 2008 Wenchuan earthquake with ALOS InSAR and GPS observations
The Ms8.0 Wenchuan earthquake occurred on May 12, 2008 in Wenchuan County, Sichuan Province, China. The devastating event caused a significant surface rupture and deformation in a large geographical area. This study intends to investigate the co-seismic surface deformations due to the main shock by integrating observations from interferometric synthetic aperture radar (InSAR) and global positio...
متن کامل