| Summary: | 博士 === 國立中央大學 === 地球物理研究所 === 97 === Due to the plate movement is considerably slow, human history record is too short to identify landscape change for such a long time scale. However, tectonic geomorphology indices can display the characteristics of tectonic movement in a long time. Therefore, the purpose of this study is to evaluate the difference of tectonic movement and characteristics of tectonic evolution between east and west sides of the orogeny in Central Taiwan, by applying a quantitative analysis of geomorphic indices coupled with mathematical fitting function, gradient index and slope vs area relationship from stream power model.
Both logarithmic and exponential function of mathematical fitting function were used to illustrate the characteristics of river longitudinal profile and the relationship with tectonic movement. Furthermore, normalized gradient index (SL/k) from the river longitudinal profile of main and tributary was used to plot the 2-D profile for illustrating the characteristics of landscape. Additionally, the concavity (θ: represented to the characteristic of landscape) and steepness ( : represented to the degree of rock lift) from the slope vs area relationship of the stream power model were further applied to examine the characteristics of tectonic movement.
The results of this study are listed as following:
1. Different results for the mathematical fitting function were found, in which most of logarithmic function were found on the west side, and most of exponential function were found on the east side. Concavity (θ) also showed the asymmetric landscape of the orogeny in Central Taiwan.
2. Normalized gradient index (SL/k) can response the behavior of rock, knickpoint, continuous-gorge, the active of rock movement, as well as the relationship between geometry of the flow path and the active trend of rock movement.
3. Average log(ksn) and the coefficient of determination (R2) of exponential and logarithmic function were similar for both sides of Central Range. Therefore, this study implied that the orogeny of Central Taiwan is in a steady state.
4. According to the quantitative analysis of geomorphic indices coupled with and SL/k, the degrees of tectonic movement trend are Western Foothills Belt > Hsuehshan Range Belt > Eastern Backbone Ridges Belt > Western Backbone Ridges Belt. Furthermore, the average precipitation in the past 50~60 years and the flow versus the normalized steepness (ksn) index exhibit no remarkable relationship. This study suggested that the control factor of stream evolution is tectonic movement, not the resistance of rock stratum nor climate.
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