基于地壳浅部实测地应力数据与数值模拟相结合的断层稳定性研究——以郯庐断裂带中段为例

Fault stability is closely related with stress state. In situ stress measurement data is the most direct reflect to stress field. Exploring fault stability with in situ stress measurements has practical utility and scientific significance. Some scholars use μ_m the radio of maximum shear stress and mean stress calculated by 2D stress measurement data to evaluate stress accumulation level. Based on Coulomb fracture criterion, Bayley's friction law and Anderson fracture theory, the researches on fault stability were carried out. But there are limits on comprehensive utilization of deep and shallow data and on quantitative analysis of deep data. Also the boundedness caused misjudge to fault stability. The research object of this topic is the middle section of Tanlu Fault Zone. Based on “Database of Crustal Stress in China and Adjacent Area”, statistical characteristics analysis on in situ stress measurements of shallow crustal in study area will be carried out. Then With multifarious data between the shallow and deep crust as a constraint, considering research achievements on active tectonics, geophysics and rock mechanics, the influences of gravity, tectonism and the mantle drag to current stress field will be simulated. Thus Deep stress quantitative analysis can be carried out. Then the fault stability of the middle section of Tanlu Fault Zone can be analyzed by calculating absolute coulomb stress. New results should deepen seismic activity understanding on the study area in future.

断层的稳定性与地应力状态密切相关，地应力测量结果是对应力场最直接的反映，探索用实测地应力数据研究断层稳定性的方法具有实用价值和科学意义。一些学者用二维实测地应力数据计算最大剪应力与平均应力的比值μ_m来评估应力积累水平，并以库伦破裂准则、拜尔利摩擦定律和安德森断裂理论为基础开展了原地应力对断层稳定性的影响分析，但在深浅部数据的综合利用与深部应力量化分析方面存在局限性，并且会导致对断层稳定性的研判出现偏差。本课题以郯庐断裂带中段为研究对象，基于“中国大陆地壳应力环境基础数据库”，开展研究区地壳浅部实测应力的统计特征分析，以地壳深、浅部多种数据作为约束，综合考虑活动构造、地球物理和岩石力学等各方面研究成果建立有限元模型，模拟分析重力、构造作用和地幔拖曳作用对应力场的影响，开展深部应力量化分析，计算郯庐断裂带中段断层的现今绝对库伦应力，分析该断层稳定性。研究成果可加深对该区未来地震活动性的认识。

郯庐断裂带是中国东部规模最大且最重要的一条断裂带，前人的研究表明郯庐断裂带的危险性正在加强，尤其是中段。前人在用实测地应力数据得到的应力积累水平μ_m值研判断裂带稳定性方面做了许多有益的探索，但研究中大多是在Anderson断层模式下，即由最大、最小水平应力和估算的垂直应力得出μ_m，且忽略了地壳深浅部应力状态可能解耦的事实，加之所用实测地应力数据少、浅、分散，可能导致断层是否稳定的判断结果不准确。.本研究以郯庐断裂带中段为研究对象，首先研究了郯庐断裂带中段现今地应力特征；然后研究了Anderson断层模式下求取μ_m的误差规律，进而校正了利用二维实测原地应力测量数据研判断层稳定性的结果；最后研究了利用三维地应力数据研判断层稳定性的方法，并利用数值模拟计算得到的断层附近深部应力量值计算结果研判断层稳定性。综合评判认为郯庐断裂带中段断层较稳定。.本项研究可提高实测地应力的应用价值和水平；有力推进用实测地应力数据研判断裂带稳定性工作的进展，为重点防范区的地震监测预报提供参考。