| dc.description.abstract | Efforts have been devoted to the study of tectonic activities at the foothill area in central Taiwan after Chi-Chi earthquake. Tectonic settings under central Taiwan is considered to be highly related to the orogenic processes, two methods, physical modeling and numerical modeling, are usually applied to study the structural evolution of the area by taking the geologic patterns of the decollement and boundary faults into consideration. Physical modeling tends to do the qualitative analysis while numerical modeling stresses the quantitative results. As a basis of finite element method, Adeli numerical modeling program has been used in this study in order to obtain a better understanding of the subsurface geologic structures in central Taiwan.
With reference to the available geological and geophysicals data, boundary conditions and material factors have been carefully selected in designing the initial structural model in the elasto-plastic half space. By stepwisely changing the main boundary fault conditions, three types of decollement design have been tested to establish a basic model for further analysis. Modeling results, such as surface horizontal velocity field and cumulated plastic deformation(CPD), are then used to correlate with the pre-921 earthquake GPS data and the earthquake distribution pattern in 1990-2002, and thus an interpretation on the characteristics of the tectonic movement is presented.
Following conclusions can be drawn from numerical modeling results:
(1) Coefficient of friction(CF) is highly significant. The model, with a CF=0.4 for the decollement as well as CF’s are in ascending order(0.1-0.5) or all equal to 0.3, shows better correlated results.
(2) Decollement should extend up to 80 km after crossing western foothill area, and then dips 40 degrees towards the east.
(3) When geologic boundary faults are arranged in imbricate pattern, modeling results are best fitted to earthquake distribution.
(4) High surface ground uplift appears at the place where decollement kinks at depth, and besides, the distribution patterns of the ground horizontal velocity and strains are also obviously influenced by the kinking of the decollement.
(5) The place between Chanhwa and Chelungpu faults will bear the highest horizontal velocity field in central Taiwan in the future. | en_US |