| Summary: | 碩士 === 國立臺灣大學 === 地質科學研究所 === 94 === When an earthquake occurs close to an urban area, it is easy to cause the collapse of buildings and other damages following by the surface rupture. It also results in unpredictable disasters. In order to estimate the amount of damages following by an earthquake, it is important to understand how an earthquake causes the surface rupture. Furthermore, the surface rupture is closely related to the underground fault geometry and subsurface structure. Thus it is necessary to obtain detail and continuous inter-seismic or co-seismic ground slips to study surface rupture fault and fault geometry.
On Sep. 21, 1999, Mw 7.6 Chi-Chi earthquake occurred in Taiwan. It causes many damages at the area of surface rupture. At the Tsaotun area, the surface rupture always occured along the Chelungpu fault (CLPF). In addition, about 2km from the east of CLPF, there was an Ailiao fault (ALF) which also created some surface deformation, thus there should be changes in co-seismic ground displacement. In previous study, a more complete measurement of the co-seismic ground displacement was retrieved from sub-pixel correlation of SPOT satellite images. The displacement distribution was used to study the surface deformation and underground geometry of the CLPF structure. However, it cannot accurately locate the position of surface rupture of CLPF and there were no obvious changes in displacement on ALF due to the low resolution of SPOT images.
In this study, the high-resolution aerial photographs are used for analysis. This study also uses orthorectification to eliminate the distortion from the topography and sub-pixel correlation to compare and analyze orthor-images, and then obtain more accurate co-semic surface displacement. The result clearly shows the location of surface rupture of CLPF and the obvious change in horizontal displacement on ALF. By east-west profiles, the changes in horizontal displacement were 4.5~5.5 meters toward west and 3~4 meters toward north cross the CLPF, and the changes of the northern segment was greater than the southern one. The changes in horizontal displacement were only 1~2 meters toward west cross the ALF, the changes zone of the southern segment was shorter than the northern one, and the greatest change was appeared in the middle of the southern segment. Therefore, the dip of northern segment was bigger than the southern one on the CLPF plan at Tsaotun, and closed to the result from level elevation changes. Further, the angle of subsurface plane should be an obvious change in the middle of the southern segment.
This study applies sub-pixel correlation to the higher resolution aerial images and provides a more accurate result than the SPOT images can. In addition to the discussion of the relationship between the fault and its underground geometric structure, this method may be able to produce the surface displacement even in the area with smaller earthquakes.
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