| Summary: | 碩士 === 國立臺灣大學 === 地質學研究所 === 87 === Geological modeling is a new way in geological studies. By the help of physical modeling and numerical modeling, we can understand the possible models of the development of the kinematics and dynamics evolution of structure. These studies try to estimate the possibility of sandbox simulation experiments in physical modeling; and try to analyze the effect of boundary conditions and main controlling factors in physical modeling. Furthermore, by using physical modeling and three-dimensional numerical modeling, we try to simulate the consequence of geological settings, oblique convergence and basement high in the inter-relationship between the development, evolution and structure in the western Taiwan. We hope that will help us understand more about the regional tectonics of Taiwan.
By the simulation of sandbox behavior, there are some conclusions: most models develop conjugate thrust faults and pup-up structures; in most cases, the same set of conjugate thrust faults developed earlier than the backthrust faults. The modeling result is highly affected by the friction coefficient of backstop; as the friction coefficient reduced, the strain would concentrate on the top part of the backstop and increase along the ramp of the backstop. The greater the angle of inclination of the backstop, the easier the forward propagation of the strain. Reduction in the angle of inclination results in the concentration of strain near the toe front of the backstop, and a set of pup-up structures could be found at the toe of the backstop. As the friction coefficient of the base reduced, the forward propagation of the strain becomes more easily. Thought the competence of materials would affect the displacement of the propagation, it is not as important as the others factors.
This research aimed to realize the effect of the basement high of western Taiwan during oblique convergence. Results: Backstop mainly affects the earlier stage of the oblique convergence; the shape of the basement and the early stage structures formed by the indent backstop controls the shape and development of later stage structures. As a consequence, forward propagation of the deformation front occurred in the central western Taiwan, because of the resistance at the front of the basement high, the deformation front propagated slowly at the front of the basement high. There is low resistance in the southern Taiwan and the sediments there are thickened, the deformation front moved forward. The above reasons may explain the S-shaped deformation front at the western Taiwan. Most thrust faults are forward-breaking sequence and it develops later in the western region. The formation of Tatu terrace, Bakua terrace, west Hengchun terrace may be the result of thrust faults; Pingtung valley, Taichung basin, Hengchun plain may be piggy-back basins. And these results are supported by the preliminary results of these experiments. Sandbox physical modeling is very useful in the research of the development and evolution of geological structures, and it showed great potential in this research. From the analysis of the parameters of the three-dimensional numerical modeling, we suggest that the interface friction angle of the basement high should be smaller than 15°. The existence of the basement high in the numerical modeling results in the change in the direction of stress field and strain field. Based on the nature of faults, we suggest that the faults near basement ramp tend to develop thrust faults and strike-slip faults would develop at later stage. Since the strain energy concentrated at the front of the West-Foothill near Chiayi and Tainan, these areas may affect by earthquakes.
|
|---|
