2013年芦山7.0级地震前后变形机制及断层力学特性模拟研究

Research about crustal deformation and mechanical properties of faults before and after Lushan M7.0 earthquake is very important to understand the earthquake preparation, occurrence and postseismic effects. Firstly, the dynamic deformation characteristics and mechanisms before and after the Lushan earthquake will be identified, and then the principal component, such as poroelastic effect, afterslip or postseismic relaxation, will be recognized from postseismic effects based on the deformation background of the Middle-Southern Section of the Longmenshan Fault (MSSLF) and the continuous GPS surveying and leveling extension measurement after the Lushan earthquake in the research area. Secondly, we will construct a dynamic viscoelastic model with multi-faults through three-dimensional Numerical Manifold Method (NMM), and simulate the differences of mechanical properties among rupture segment, locked segment and the fault segment under the inadequate strain release status of the SSLF after the Lushan earthquake constrained by the deformation data before and after the Lushan earthquake. Furthermore, the dynamic characteristics of stress/strain evolution for these different fault segments will be summarized. Lastly, the estimated results of the seismogenic stage for the locked segment based on analyzing the dynamic deformation features and simulated mechanical properties of faults will be presented.

芦山地震前后地壳变形特征和断层力学特性的研究对认识此次地震孕育、发生和震后影响十分重要。首先，本申请基于龙门山断裂带中南段背景变形资料，开展该区GPS连续站持续观测和水准测线加密测量，研究给出芦山地震前后变形动态特征描述和机制解释，识别出震后变形可能包含的主要成分（孔隙压力反弹、震后余滑或粘弹性松弛）。随后，通过三维数值流形方法（NMM）建立多断层系统的粘弹性动力学模型，以芦山地震前后地壳形变资料为约束模拟给出龙门山断裂带中南段断层破裂段、断层闭锁段和芦山地震应变释放不充分断层段的力学特性差异，总结上述不同类型断层段的应力、应变动态变化特征。最后，综合分析研究区域地壳变形动态特征和断层力学特性模拟结果，给出龙门山断裂带中南段非破裂断层段可能处于的孕震阶段估计。

基于GPS等大地测量资料，对比研究了4种数据网格化方法，识别了芦山地震前后地壳变形特征及机理。具体研究结果包括：①基于模拟和实测GPS数据，从抗差性、边缘效应、误差分布、稳定性等角度研究了4种网格化方法，显示最小二乘配置方法表现最佳；②GPS应变率结果显示，汶川、芦山地震处于东西向挤压应变率积累高值区边缘，芦山地震后龙门山断裂带南段的应变率存在集中-弱化过程；③基于GPS剖面和时间序列结果估算了汶川地震对龙门山断裂带的加载效应，量值相当于震间期约69年的总和；④芦山震后水准资料显示，龙门山断裂带南段存在垂直隆升现象、巴颜喀拉地块内部量值大于断裂带、呈现连续变形特征；⑤芦山地震的震后变形以余滑和粘弹性松弛为主，震后短期以余滑为主（近场量值约相当于粘弹性松弛的25倍）、长期远场以粘弹性松弛为主；⑥汶川震前龙门山断裂带全线强闭锁，2009–2011年龙门山断裂带南段呈强闭锁状态、2011–2013，2013–2015和2015–2018时段芦山地震震源位置西南方断层处于强闭锁状态、汶川至芦山破裂空段的闭锁程度也较强但空间范围小于前者；⑦基于1999–2018多期GPS为约束的数值模拟结果显示，汶川-芦山地震破裂空段的库仑应力增长速率在2009-2018期间显著增加；⑧识别了中国大陆及周边8次7级以上大地震发生地点与应变率分布的关系，发现强震均发生在与其构造背景一致的应变率积累高值区边缘。总体上，GPS网格化方法的研究，为变形场描述、数值模拟边界约束、监测台网布局等提供了方法基础；强震变形及机理研究，对于认识区域强震活动、大陆内部7级强震的震后变形机理、中国大陆7级以上强震发生地点判定均具有重要科学意义，整个项目研究对于探索强震物理预测具有促进作用。