1999年9月21日集集大地震重創台灣，除造成草嶺與九份二山兩處大山崩外，同時也使中部山區發生數千處大小不一的山崩。李錦發等人以數值航測技術進行山崩立體判釋，圈繪紅菜坪地滑分佈位置及影響範圍，根據其圈繪結果，紅菜坪地滑地之滑動面積廣達100多公頃，此與滑動面積亦超過100公頃之九份二山只相距約2公里。然而，根據區域地質圖以及地形圖，得知九份二山與紅菜坪現地地質、地形條件類似，受集集地震之影響也相似，但紅菜坪之滑動相對於九份二山山崩卻較緩慢，造成兩大型山崩之運動特性差一之原因值得深入探究。本研究根據現地調查確認紅菜坪地滑之滑動區域面積約88.6公頃，滑動材料則為厚層崩積層，根據滑動體地表位移方向及地形特徵，研究將紅菜坪滑動塊體分為三塊（滑動塊體A、滑動塊體B、滑動塊體C），其中滑動塊體A主要為崩積層沿頁岩層面滑動。其次蒐集中央氣象局於紅菜坪地滑地以及九份二山地滑地附近之強震資料(12地震測站)，除分析強震資料之方向性外，並利用累積位移分析法計算強震引致邊坡位移之方向性。結果發現水平加速度、艾氏震度以及邊坡永久位移之最大值幾乎分佈於E ~W及WNW ~ ESE等方向。本研究定量計算集集地震對紅菜坪地滑地及九份二山地滑地運動特性之影響，逆分析結果顯示，九份二山之破壞摩擦角比紅菜坪大2.6°，根據引入速度相關摩擦率累積位移量計算結果，得知九份二山之地質材料對於滑動速度之影響比對紅菜坪影響敏感，由此可知，此二大型滑動之運動特性與震波方向、坡向、地質材料以及構造特性皆有相當大的關係。 The Chi-Chi Earthquake (Mw=7.6) of September 21, 1999 triggered many landslides in central Taiwan. Two of these landslides, Hungtsaiping and Jiufengershan were gigantic landslides. The distance between these two landslides is 2km. The kinematic of these two landslides is significant different. Jiufengershan landslide was a catastrophic rockslide-avalanche and the Hungtsaiping landslide was relatively slow-moving. This research explores the geological factors accounts for the differences. Factors such as the characteristics of strong-motion, geology and geomorphology were considered in the study. Based on the site investigation, the mechanism of Hungtsaiping landslide is studied. The sliding area is 88.6ha. Three slid masses(slid mass A, slid mass B, slid mass C) are identified. Thick colluvium sliding along bedding plane of shale are also identified. An analysis of 12 strong-motion records collected in the concern area showed that the distribution of horizontal pseudostatic coefficients and earthquake energy ratio were anisotropic. The principal direction of strong-motion is mostly in the E/W~ESE/WNW trending. The maximum permanent displacements computed using the strong-motion records and a modified sliding-block method were also direction-dependent and oriented in the trend of E/W~ESE/WNW. This direction is perpendicular to the trend of the main geological structures of the studied area. The back calculated friction angle that corresponds to a critical land mass displacement for the Jiufengershan landslide is about 2.6º larger than that of Hungtsaiping landslide. The material on the sliding surface in Jiufengershan should be more velocity-dependent than that of the Hungtsaiping landslide according to the back calculations. The difference of the friction angles of the sliding surface of two study landslides. The difference of the friction angles of the sliding surface of two study landslides is oriented from the different slid materials. The importance of direction-dependent strong-motion, slope aspect, and mechanical properties of sliding surface on the kinematics of two nearby deep-seated landslides is demonstrated.
