汶川震区北川县城泥石流源地特征的遥感动态分析

REMOTE SENSING IMAGES BASED OBSERVATIONAL ANALYSIS ON CHARACTERS OF DEBRIS FLOW SOURCE AREAS IN BEICHUAN COUNTY OF WENCHUAN EARTHQUAKE EPICENTER REGION

汶川地震导致山地斜坡积累了大量碎屑物质,在降雨作用下极易成为泥石流源地。震后的2008年9月24日一场暴雨导致北川县境内72条沟同时暴发泥石流。本文选择了汶川地震高烈度区的北川县城8条泥石流沟流域为研究区,基于遥感手段开展了震后和相继暴雨后的泥石流源地变化特征。强震后泥石流流域的重要变化是在沟谷内诱发了大量滑坡。通过开展遥感解译和野外调查,重点分析了研究区泥石流源地的滑坡活动。将5.12汶川地震后的2008年5月18日获取的航空图像与9.24暴雨后获取的2008年10月14日SPOT图像相比较,发现泥石流源地的地震滑坡面积由153.7×104m2增加到暴雨后的191.2×104m2,即汶川高烈度区一场暴雨过程新增滑坡面积达24.4%。根据SPOT图像解译,暴雨后泥石流沟床中的松散堆积物增大到9.7×104m2。上述研究结果表明汶川震区在强降雨条件下发生泥石流的敏感性特别高。

Wenchuan Earthquake produced abundant debris left behind on the hillside slopes.The debris would later serve as the source materials for rainfall-induced debris flow hazard.On 24th September 2008,a total of 72 debris flows were triggered by heavy rainfall in the central part of the epicenter region affected by the Wenchuan Earthquake.The Beichuan County in the central epicenter region is chosen for analyzing the change of debris flow source area after the earthquake and also following a rainstorm.Significant differences after the earthquake are noticed in producing a large amount of landslides for debris flow occurrence.Interpretations of aerial photographs and SPOT images as well as field investigations are used to identify landslide occurrences in the debris flow watershed for exploring the initial conditions triggering debris flows.Comparison of the aerial photographs taken on 18th May 2008（after the 5.12 Wenchuan earthquake） with the SPOT 5 images taken on 14th October 2008（after the rainstorm event on 24th September 2008）indicates that the landslide area in eight debris flow watersheds increased from 153.7×10^4 m^2 to 191.2×10^4 m^2 during that period of time.Measurement of the SPOT images reveals that the loose sediment areas on the channel beds had further expanded to 9.7×10^4 m^2 after the rainstorm.The present results show the Wenchuan Earthquake affected area is particularly susceptible to debris flow occurrence after heavy rainfall events.