| 摘要: | 本研究收集接近集集地震發生前後的SPOT衛星影像以及航空照片來判釋山崩，並且利用地理資訊軟體MapInfo建置山崩圖層，探討集集地震所誘發山崩的特性，包括分布、數量及面積，並分析其與地震震央距離、岩性、區域地質構造、水系、道路、坡度及坡向等因子間的關連性，期能了解地震發生時，可能發生山崩之範圍及分布。並由震度衰減的比較，探討台灣地區地震誘發山崩的面積及數量與世界平均值之間的差別，及造成這些差別的原因。 經比對地震前後崩塌地圖層及野外調查檢核之後，集集地震一共誘發了9272個面積大於625平方公尺的山崩，總面積約為127.8平方公里。在烈震區地震加速度250gal以上區域所發生的山崩共有8843個，總面積為123.8平方公里，佔全部因地震所誘發之山崩的面積百分比為96.8%，山崩位置略呈橢圓狀分布，長軸方向大約是北北東的方向，與此區域之區域構造方向約略平行。由各項分析結果顯示：（1）山崩的分布大部分都在水平最大地動加速度250gal以上的區域，進一步分析則可以發現，崩壞比在300gal之後明顯的增加。（2）山崩大多發生於距斷層破裂面20公里以內的距離，而分布最遠的距離為60∼70公里的區間內。（3）山崩的分布與地層也有很大的相關性，山崩有明顯集中在頭嵙山層、錦水頁岩及達見砂岩的現象，尤其是頭嵙山層火炎山岩像更表現出相當高的崩壞比。（4）崩塌地大多分布在坡度大於100%的邊坡。（5）集集地震所誘發山崩分布的坡向在上盤處以S及SE兩個坡向崩壞比最大，在下盤處則以SE、S及SW三個坡向崩壞比較大，顯示此次集集地震主要是由東南向西北運動。 A large number of landslides were triggered by the Chi-Chi Earthquake (ML 7.3) on 21 September 1999. These landslides have been mapped from satellite images in this study. By using GIS (Geographic Information System) as a tool, we can construct a GIS table of landslides triggered by the earthquake and analyze their characteristics, including types, distribution, areas and numbers, …etc. The distribution and areas of landslides have been compared with the distance from the earthquake foci, rock types, faults, roads, rivers, hill slopes and slope directions. There were 9272 landslides occurred during earthquake shaking within the area greater than 625 square meters and total area of landslides is 127.8 square kilometers. There were 8843 landslides located within the area of PGA value 250gal and above. These landslides were distributed in an ellipse-shaped region with the major axis striking NNE, coinciding with the trend of regional faults. Statistics shows the following results: (1) Landslides almost located within the area that PGA greater than 250gal, especially within the area that PGA greater than 300gal. (2) A lot of landslides occurred within 20Km from the fault rupture plane. The longest distance from the rupture plane located at the interval of 60 to 70 Km. (3) the Toukoshan Formation, The Chinsui Shale and the Tachien Sandstone were more easily influenced by the earthquake shaking, especially at Huoyenshan Facies. (4) slopes with inclination larger than 100% involves more landslides. (5) At the hanging wall, most slopes collapsed at S and SE facing. At the foot wall, most slopes collapsed at S , SE and SW facing, whereas slopes facing to other directions were not so seriously damaged. It shows that the main movement of Chi-Chi earthquake is from SE to NW. |
