汶川地震前后滑坡分布变化规律——以川北山区为例

Change law of landslide distribution before and after Wenchuan earthquake:a case study of mountainous area in northern Sichuan

为获取汶川地震效应下滑坡空间分布的变化规律,针对川北山区2002-2010年的滑坡案例数据,构建了4个表征不同时间尺度的滑坡子集,对比分析了汶川地震同震滑坡、地震前后降雨型滑坡的个数、比例、密度以及与滑坡发生密切相关的5个因子(坡度、岩性、高程、距断裂带距离和降雨)的敏感性。结果显示,汶川地震震后3年中,中型滑坡的比例由震前的2.29%增大至16.86%;滑坡的坡度优势区间由10°~15°推高至30°~45°,高程优势区间由400~600 m推高至800~1200 m,距断裂带距离的优势区间由震前0~15 km缩短至0~10 km;松散堆积层上滑坡分布密度迅速扩大;滑坡对降雨的反应时间较震前明显缩短,且震后滑坡的临界降雨量值较震前降低。这些结果表明,汶川地震的发生改变了川北山区的滑坡发育条件。

The purpose of this study is to analyze change law of spatial distribution pattern of landslides before,during and after the Wenchuan earthquake. The landslide data,recorded in mountainous region of northern Sichuan between 2002 and 2010,was split into 4 subsets according to the landslides ' occurrence time. The landslides number,proportion,density and susceptibility were comparatively analyzed to determine how the occurrence of landslides correlates with slop,lithology,elevation,distance from fault and precipitation. Results show that during the three years after earthquake,( 1) the proportion of medium-scale landslides increases from 2. 29% to 16. 86%;( 2) dominant interval of the landslides increases from 10°- 15° to 30°- 45° in slope,from 400- 600 m to 800-1200 m in elevation,whereas decreases from 0- 15 km to 0- 10 km in distance from fault;( 3) the density of landslides initiated in the loose sediments increases;( 4) the responding time of landslides to rainfall reduces obviously and the rainfall threshold of landslides lowers. Hence,these results confirm that the occurrence condition of landslides in the study area changes after the Wenchuan earthquake.