| Summary: | 博士 === 國立中央大學 === 地球物理研究所 === 93 === A study on the estimation of earthquake ground deformation and its attenuation
Chien-Fu Wu
Abstract
Strong ground shaking caused by a major earthquake may induce great damage. However, large fault rupture and ground deformation and failure may also have big destructive power to structures. In order to realize the effects of rupture process of shallow fault to the distribution of ground deformation, the following works were done in this study. (1) Modify the existing finite element program and design some appropriate shallow crustal structures to calculate the ground deformation induced by different fault ruptures with various geometry, source mechanism, and slip distribution. The computed ground deformation data were then used to analyze the attenuation relations of ground deformation with respective to source distance for different magnitude. (2) Integrate the acceleration data of the Chi Chi earthquake, collected by TSMIP (Taiwan Strong Motion Instrumental Program conducted by Taiwan Central Weather Bureau), to the corresponding displacement records and then some analyses are made to their peak values.
Since 1990 digital strong-motion accelerographs and Globe Position System (GPS) instruments have been widely deployed in the Taiwan region (Shin et al., 2003; Yu et al., 2001). The 1999 Chi-Chi, Mw 7.6 earthquake and the 2003 Chengkung, Mw 6.8 earthquake were well recorded by both digital accelerographs and GPS instruments. These data offer a good opportunity to determine permanent displacements from the strong-motion records and to compare the results with those derived from the GPS measurements. As noted by Boore (2001), a double integration of the acceleration data often leads to ridiculous results, and baseline corrections are therefore required in most cases before the integration step. Based on the pioneering work of Iwan et al. (1985) and Boore (2001), this study developed an improved method for baseline correction and validated it using an extensive set of data from shaking table test of a known displacement on 249 accelerographs. Our baseline correction method recovered about 97% of the actual displacement from the shaking table data. We then applied this baseline correction method to compute permanent displacements from the strong-motion data of the Chi-Chi and Chengkung earthquakes. Our results agree favorably with the coseismic displacements determined by the GPS measurements at nearby sites. The ratio of seismic to geodetic displacement varies from 0.78 to 1.41, with an average ratio of about 1.05.
Near field peak ground displacement(or permanent displacement) attenuation relationships are deduced with data from improvement finite element method. They are
（1） strike slip fault
log（Y）= -1.393+ 2.216×log（sqrt(A)）–3.049×log（R+sqrt(A)）-0.003×R
（2） thrust fault （dip angle 30 degree）
Hanging wall
log（Y）= -1.479+ 1.665×log（sqrt(A)）–1.945×log（R+sqrt(A)）-0.004×R
Foot wall
log（Y）= -1.437+ 1.138×log（sqrt(A)）–0.872×log（R+sqrt(A)）-0.036×R
Where Y is the amplitude of displacement in meter, A is fault rupture area in square kilometers, R is rupture distance in km.
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