以SPOT衛星影像探討1999集集地震後之崩塌行為

Analysis of Landslide Behavior after 1999 Chi-Chi Earthquake by SPOT Satellite Images

壽克堅(K. J. Shou) ； 吳秋靜(C. C. Wu) ； 許惠瑛(H. Y. Hsu)

《航測及遙測學刊》 15卷1期 (2010/03) Pp. 17-28

https://doi.org/10.6574/JPRS.2010.15(1).2

摘要

台灣地區受到1999年集集地震之衝擊，地質破碎坡地崩塌嚴重；加以近年來受氣候變遷影響造成颱風降雨強度增強，使得原本脆弱的坡地更易遭受侵襲並造成崩塌災害。本研究以多時期SPOT衛星影像探討1999集集地震後之崩塌行爲，爲了利用衛星快速對大範圍地區進行崩塌地調查，本研究採用常態化差異指標－坡度(NDVI-Slope)雙門檻值法來做崩塌地判釋。此一雙門檻值法首先利用NDVI值作爲分界門檻值找出裸露地，再搭配DTM坡度門檻值將崩塌地進一步判釋出來。但此一雙門檻值法之的判釋可能會受地區性的地形條件、地質條件、植生條件等影響判釋之準確度；因此，不同之流域選用不同之判釋門檻值有其必要。本研究以烏溪爲研究區域，考慮賀伯、桃芝、敏督利等三個颱風事件探討各種NDVI及坡度門檻值組合對崩塌地判釋之影響，並以全區域及地層年代分區探討崩塌地之行爲。本研究以接受器操作特性曲線(Receiver Operating Characteristic Curve)來分析比較出最佳的門檻值組合，以進行崩塌地有效快速判釋。本研究發現NDVI門檻值設爲0.1坡度門檻值設爲40%在烏溪以全區域及以地層年代分區的分析有一致性較佳之判釋結果。多時期崩塌判釋結果發現，2001年桃芝颱風時西側靠近車籠埔斷層地區有顯著崩塌地分布外，因桃芝颱風之降雨落在北港溪一帶，使得該區崩塌地比以往更爲嚴重。2004年的敏督利颱風，因強降雨造成烏溪流域西北側有顯著崩塌，強降雨未落於北港溪流域，相較桃芝颱風北港溪流域之崩塌有明顯減緩趨勢。集集地震引起的崩塌地在自然癒合但未達邊坡長期穩定狀態下，後續颱風事件仍會因降雨而產生坡地災害，但地震之衝擊效應將隨時間而衰減。

關鍵字

SPOT ； NDVI-Slope雙門檻值法 ； ROC曲線 ； 烏溪 ； 1999集集地震

並列摘要

Due to the impact of 1999 Chi-Chi Earthquake (MW=7.6), the geology in Taiwan area was more fractured and a tremendous amount of landslides were induced. After 1999, the unusual typhoon events cause the primary and secondary landslide hazard more severe. This study aims to study the landslide hazard by the SPOT satellite images, focusing on the behavior of the primary and secondary landslide hazards after 1999. In order to obtain the landslide distributions efficiently, this study adopted an NDVI-Slope criterion in the GIS image interpretation. Since this criterion could be affected by local topography ore geology, it could be necessary to adopt different criterion for different catchment or sub-catchment. In this study, the Wu His catchment in Central Taiwan was adopted as study area, the landslides induced by three typhoon events, i.e., Herb (1996), Toraji (2001) and Mindulle (2004), were analyzed. In order to obtain an optimal criterion, the analysis of Receiver Operating Characteristic Curve was used. The results showed good interpretation by using the criterion 0.1 of NDVI and 40% of slope in Wu His catchment, for the whole catchment and for its sub-catchments.
The landslides distributions showed that significantly more landslides were induced near the Chelungpu Fault by the 2001 Toraji Typhoon. In addition, more landslides were found in the upstream Peikang River sub-catchment, due to the distribution of heavy rainfall. However, less landslides were induced by 2004 Mindulle Typhoon in the Peikang River area, since the heavy rainfall is distributed in the northwestern side of the catchment. The results reveal that the self-healing effect is undergoing, but subsequent typhoon events could still cause above-normal landslides. However, the impact of landslide will decay away gradually.

並列關鍵字

SPOT ； NDVI-Slope Criterion ； ROC Curve ； Wu Hsi ； 1999 Chi-Chi earthquake