Retreat rate and evolution of knickpoints caused by the 1999 Chi-Chi earthquake
Lu, Hung Yu
Liao, Jyh Jong
|關鍵字:||遷急點;軟岩;倒退機制;倒退速率;knickpoint;weak rock;retreat machanism;retreat rate|
本研究建立集集地震造成遷急點之歷年倒退資料目錄，利用交通大學(2012)、Hayakawa and Matsukura (2003)等遷急點倒退率經驗迴歸式進行迴歸測試，公式中考慮因子包含水流流量、遷急點的落差與坡降以及沖蝕指數Kh等因子，結果顯示有幾個遷急點實際倒退速率大於回歸出來的倒退速率，推測為倒退機制的差異造成。|
The Chi-Chi earthquake occurred on 21 September 1999. This earthquake produced surface ruptures of 100 km in length along the Chelongpu fault, which strikes in north-south direction. The knickpoints formed at the river channel owing to the uplift of the Chelungpu fault. The bedrock of the knickpoints belongs to the geological provinces of the Western Foothills. The Western Foothills are composed of the Late Cenozoic sedimentary rock which is usually weak and poorly cemented. Severe incision in the weak bedrock was activated after its armor layer was removed. The maximum annual rate of kninkpoint retreat reached hundreds of meters. Based on aerial photographs/orthophotographs, derived Digital Elevation Data, cross-section surveyed data, and field investigation, morphological changes and retreating processes of the kninkpoints were evaluated. The mechanisms of the knickpoint retreat were concluded into four types: 1) plane sliding; 2) overhang falling; 3) abrasive erosion; 4) block plucking. The conceptual models of the knickpoint retreat were also proposed in this study. Two empirical formulas of the knickpoint retreat rate were verified with the knickpoints data. The results suggest that the empirical formulas might be not suitable for cases of knickpoints caused by earthquake uplift, which could be improved by considering the mechanisms of knickpoint retreat.
|Appears in Collections:||Thesis|
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