巴颜喀拉地块周缘断裂大震序列的触发机制

Bayankala block bounded by three sets of faults including East Kunlun fault and Xianshuihe fault and Longmenshan fault, which controls a series of strong earthquakes, is a seismically active area in China. There were several strong earthquakes continuously occurred in the region in recent years to promote the recognition of movement characteristics of the faults and seismic activity and further research on earthquake triggering mechanism. In the application, the changes of stress and strain caused by the four strong earthquakes with M≥7 recently occurred in the system constituted with faults and active blocks are researched on and triggering mechanism of strong earthquake is discussed based on characteristics of fault activity and the data of seismic and geologic and the data of GPS observation data and tectonic stress field. The study will provide a theoretical basis and foundation for seismic risk evaluation and mid-short term earthquake prediction. The main contents include are as follows.① The three-dimensional geometric model and segmentation model of the major active faults are established based on existing geological data. ② The model boundary constraints are determined based on data of GPS and tectonic stress field. ③The parameters of the model are determined and the appropriate geotechnical constitutive law is chosen for fault interface combining geological data and historical seismic data of the faults. ④The mechanics and motion state of studied system before and after the destructive earthquakes is simulated.

巴颜喀拉地块由东昆仑断裂带、龙门山断裂带和鲜水河断裂带三条巨型活断层围限，其控制着一系列强震的发生，是我国地震活动最强烈的地区之一。该区域上近年来强震的连续发生加深了对块体周缘断裂的运动特征和地震活动性的认识，促进了对强震之间的触发机制的进一步研究。本申请基于断层的活动特征、地震地质资料、GPS观测数据及构造应力场等资料，研究断层-活动地块系统内近期发生的４次Ｍ≥７级的强震序列引起的应力、应变状态的变化，探讨强震之间的触发机制，为地震危险性评价、地震中短期预测提供理论基础和依据。研究内容包括：①收集已有的野外地质调查资料，建立主要活动断裂的三维几何模型和分段模型；②依据GPS监测数据及构造应力场资料确定模型边界输入；③结合地震、地质资料，确定模型参数，选择合适的岩土本构关系运用于断层界面；④对系统内4次大震发生前后的力学和运动状态进行数值模拟，研究先发大地震对后发大地震的应力触发作用。

巴颜喀拉地块由东昆仑断裂带、龙门山断裂带和鲜水河断裂带三条巨型活断层围限，其控制着一系列强震的发生，是我国地震活动最强烈的地区之一。该区域上近年来强震的连续发生 加深了对块体周缘断裂的运动特征和地震活动性的认识，促进了对强震之间触发机制的进一步研究。本项目归纳总结了强震触发机制的研究现状，指出现有研究存在的不足；收集整理了巴颜喀拉地块的构造环境与动力学背景资料，以及其周边的三条大断裂-东昆仑断裂带、龙门山断裂带和鲜水河断裂带的地震地质资料，分析了其活动特征；收集了区域范围内历史地震和现代仪器记录资料并进行编目，分析了研究区域内主要发震断层上的历史强震及现代小震活动状况和特点；建立了巴颜喀拉地块和周边三条断裂带的几何模型；从数学、力学角度描述了地震发生的过程，在此理论基础上，选择与率和状态相关的摩擦本构关系运用于断层界面；收集整理了研究区域的构造应力场资料及GPS监测数据，以此为参考确定模型的初始约束条件；以断层-活动地块体系为研究对象，对昆仑山口地震、汶川地震、玉树地震和芦山地震发生前后研究区域的力学和运动状态进行了数值模拟。结果表明，前次大震发生后的应力、应变和位移状态与下次大震的发生存在一定的联系，每次大震发生后，其震中附近地段的应力、应变会有所释放，分布也变得相对均匀，而应力、应变较大且分布有突变的区域往往是下次大震发生的地段。依据上述规律，初步推断巴颜喀拉活动地块及周边区域未来可能发生强震的地段为鲜水河断裂带的甘孜-道孚段、龙门山断裂带的西南段和东北段。本项目的研究成果为研究区域内的活断层地震危险性评价及震后趋势预测提供了理论基础和科学依据，为其它地震频发区在该方面的研究提供了参考方法。