云南省丽江大地震及其诱发的崩塌滑坡灾害特征

LIJIANG EARTHQUAKE AND THE INDUCED ROCKFALLS AND SLUMPS IN YUNAN

１９９６年２月３日，云南省丽江县城以北４０ｋｍ发生７级强烈地震，这次地震在约１２０００ｋｍ２范围内诱发了至少４２０处中小型崩塌和３０处大中型滑坡，造成房屋倒塌、桥梁毁坏和公路堵塞。调查研究得出以下结论：（１）地震触发的崩塌滑坡分布在Ⅵ度区内，主要集中在主震震中东南部，接近表层构造断裂带和余震活动范围内；（２）崩塌主要发生在高陡斜坡的峡谷地带，滑坡多为复活型，部分为同发型和滞后型滑坡；（３）地形是控制崩塌滑坡分布位置的主导因素，崩塌多发生于大于６０度斜坡中上部，滑坡发育于中缓斜坡（２５°～４５°）；（４）滑坡影响区如遇充足的降雨可能进一步变形破坏，大量地裂隙孕育着新的崩塌滑坡，潜在危险性大。

A strong earthquake occurred in Lijiang area in Yunnan Province,southwestern China on February 3,1996.The magnitude of 7 0 on the Richter scale placed this earthquake among the strongest events in China during the 1990's.The epicenter was determined to be at 27 18N and 100 13E,where is located in the seismically active region of the Hengduan Mountains,which belong to the Alpine Himalaya seismic belt.The earthquake triggered more than 420 small to moderate scale rockfalls and 30 moderate to large scale slumps throughout an area of 12,000 km 2 based on the field investigation after the earthquake.Because of the widespread landslides,the earthquake has provided a great deal of information and insight regarding seismically induced landslides.This study leads us to the following generalizations: (1)The earthquake triggered landslides were concentrated in south southeast of the epicenter of the main shock,adjacent to the area of tectonic ruptures at the surface and within the area of principal aftershocks.The landslides distributed mostly within the area with modified Mercalli intensity Ⅵ. (2)The predominant types of landslides induced by this earthquake were rockfalls,debris slides and slumps.Rockfalls were on steep walled canyon faces cut in well fractured basement rock,easpecially along the Baishui dainages and Hutiao Canyons.Slumping was found largely on reactivated,preexisting landslides,and some is incipient. (3)Topography was a key factor in controlling the location and extent of landslides in all affected areas.Rockfalls occurred on very steep(steeper than 60°) canyon slopes and ridges,and largely initiated in the upper parts of slopes.Slumps occurred on gentle(approximately 25°～45°) slopes. (4)The presence of preearthquake landslides also contribute to slope instability during the earthquake,which showed obviously reactivation,in the sence that they were generally characterized by many new open cracks of fissures. (5)Most incipient and reactivated landslides have the potential of further failure if they receive sufficient rainfall in the affected areas.Widespread ground fractures in broad area are closely related to landslides.