云南鲁甸6.5级地震次生特大地质灾害的特征及原因

Characteristics and Causes of Super-huge Secondary Geological Hazards Induced by M6.5 Ludian Earthquake in Yunnan

鲁甸6.5级地震造成特别重大灾害,所产生的次生地质灾害也达到了特大型。经过全面排查分析,地震次生地质灾害表现出6项特征:低震级大灾害、沿发震断裂密集分布、顺峡谷带状延展、近场地灾严重、散裂岩土体地灾高发、工程边坡崩滑多。形成这些特征的原因主要有以下几点:高原斜坡地带,活动断裂密集发育,地震能量沿断裂释放顺走向延伸远、垂直影响窄;峡谷纵横,谷坡陡峻,散裂岩体厚大,地质灾害易发,崩滑规模巨大;近场地震地面运动加速度大,震害强烈,向外延伸加速度值衰减较快,远场震害轻微;人类工程切坡、毁坏森林对地震次生地质灾害的产生有明显的影响。地震次生地质灾害应急排查主要应在近场区逐村排查,远场区采取有报再查的方式。

During the Ms6. 5 earthquake in Ludian,major disasters had been caused and secondary geological hazards had also reached Extra-large level. Investigation and analysis indicate that there are six characteristics of secondary geological hazards in the earthquake： the small earthquake magnitude with large disasters,the intensive distribution along the seismogenic fault,the banded extension along the canyon,serious near-filed geological hazards,the high incidence of geological hazards in areas with cataclastic rock and loose soil,more avalanche and landslide hazards on the engineering slopes. The main reasons for the formation of these characteristics include the following four aspects. Firstly,in the plateau slope zone,active faults develop intensively. The seismic energy releases and extends far along faults strikes,which causes narrow vertical influence. Secondly,in these canyon areas and steep valley slopes,there is large volume of cataclastic rock and loose soil. They are geological hazard incidental zones,and the scale of avalanche and landslide is usually very huge. Thirdly,in earthquake near-field areas,the ground motion acceleration is large and earthquake shocks are strong. However,the acceleration decays rapidly when extending outward,and earthquake shocks are weak in far-field areas. Fourthly,engineering slope excavation and deforestation have a significant impact on the generation of seismic secondary geological hazards. The emergency investigation of secondary geological hazards is conducted mainly in the villages of near-field areas. In far-field areas,it is better to investigate only if the administrator has received the message of geological hazard hidden danger.