从水井岩大型滑坡表面高温降解喷出物特征到汶川地震天然气体溢出爆炸模型  

Features of Craters and Test Results of Ejecta Distributed Above Shuijingyan Rock Avalanche in the Wenchuan Earthquake

作　　者：尚彦军[1] 刘嘉麒[1] 夏燕青[2] 刘大安[1] 雷天柱[2] 张路青[1] 

机构地区：[1]中国科学院地质与地球物理研究所工程地质力学重点实验室,北京100029 [2]中国科学院地质与地球物理研究所兰州油气资源研究中心,兰州730000

出　　处：《吉林大学学报（地球科学版）》2014年第1期230-248,共19页Journal of Jilin University：Earth Science Edition

基　　金：国家"973"计划项目(2010CB732001);中国科学院重点部署项目(KZZD-EW-05-02);国家自然科学基金面上项目(41372324)

摘　　要：汶川大地震中XI级烈度区内水井岩滑坡现场等地爆炸声、特大型滑坡现场巨大环形坑和远距离抛射碎石等记录和现象,需给出科学解释。在地震发生后多次现场地质调查和走访、样品采集和多项分析测试及其结果比较等基础上,对主中央断裂F2控制的下盘陈家坝水井岩大型滑坡体上环形坑周边不同距离范围内散落烧焦残留的硅酸盐和碳酸岩等采样后,开展了物质成分和微观结构分析。结果发现:与原生溶蚀灰岩、薄层煤岩结构和有机质成分不同,这些抛散在滑体表面的样品中富含经强烈高温作用的块石,一些成分以锰碳酸盐岩等为主的暗棕色样品中稠环芳烃是其经历过强烈热作用过程而使有机质发生环化芳构化反应的结果,即样品经过了强烈热降解作用,显示其形成时出现强烈热作用过程和高温裂解现象。结合本区地质构造特征和煤层气分布情况、地震后实施的汶川地震带深钻在穿越主中央断裂带F2深度处监测到余震过程中甲烷含量异常增高、东河口地震遗址公园发现温泉及天然气溢出等资料和研究结果,讨论了地震诱发的富含甲烷的天然气爆炸,其加剧或伴生着地震次生地质灾害。由此推测:与碳质岩或煤系共存的喀斯特溶洞中封闭煤层气在地震过程中突溢和爆炸燃烧,叠加或放大了地震作用,结果在滑坡堆积体表面残留了多处环形爆炸坑,引发了一些岩块大规模长距离水平抛撒等。研究结果对监测和认识发震断层带在地震过程中天然气爆炸诱发和加剧滑坡灾害有重要意义。Scientific interpretations are required for some abnormal phenomena at the XI intensity region of the Wenchuan earthquake ：explosion bangs ,large size circular pits and far distance flying rock avalanches .During field surveys we found circular pits and ejecta distributed above the Shuijingyan rock＆amp;nbsp;avalanche at Beichuan County in June 20 ,2008 ,about one month after the main shock .According to field investigation and lab test results ,the fired ejecta around craters are mainly carbonate manganese mixed of corrosion limestone and manganese underground surface .The brown porous ejecta are featured by intensive thermophilic degradation because they had high content of polycyclic aromatic hydrocarbons .If the regional geological conditions and coalbed gas distribution are considered ,together with some updated findings of abnormal high content of methane monitored at the depth of central active fault F2 during aftershocks ,it is inferred that the main shock induced gas explosion ,the latter triggered and enhanced some huge scale rock avalanches . The methane is stored within corrosion caves in limestone which interbedded with carbonaceous rocks ,and closed fissures near the F2 .At the lower wall the local explosions left circular pits and fired eject around the pits ,triggered and enhanced the following rock avalanches to fly far distances .The result presented is significant for monitoring the natural gas explosions in great shock and understanding its functions to large scale rock avalanches .

关 键 词：汶川地震 环形坑 碳酸盐锰质岩 煤层气 高温降解 

分 类 号：P642.22[天文地球—工程地质学]