中国大陆近年若干强震同震震间和震后应力转移及地震危险性研究

The study of stress transfer focuses on physical mechanism of seismogenic fault. By thoroughly investigating the coseismic,postseismic and interseismic stress transfers in earthquake cycle, we devise novel algorithms for extracting spatiotemporal characteristics of crustal stress signal and seperating this signal into different portions such as coseismic jumping, postseismic transient decaying and interseismic long-term loading ones in order to figure out which signal is the most dominant to control the behavior of earthquake faulting. We next develop a crustal stress model which is useful for analyzing postseismic signal of crustal deformation with the consideration of time-dependent poro-elastic pressure and earth's spherical layering effect. We further build an error estimator of Coulomb stress by introducing a random parameter space of stress tensor, receiver fault and friction coefficient in the light of their uncertainties in practice, which is extremely significant to quantitatively assess the robustness of the results of any Coulomb stress analysis. We finally construct a physical-based model for earthquake prediction with the combination of Coulomb stress model and its error estimator as well as the modifed rate- and state-dependent friction law. Accordingly, a self-consistent theoretical framework incorporating those algorithms and various models as mentioned above is indeed ideally suited to describe crustal stress signal in different phases of earthquake cycle and thereby is powerful to perform Coulomb stress analysis..Furthermore, in the context of this mathematical framework we explore the coupling mechanism between earthquake stress triggering and crustal stress field in the whole earthquake cycle with case studies of some recent strong earthquakes as the 2008 Mw7.9 Wenchuan earthquake, the 2008 Mw7.1 Yutian earthquake and the 2010 Mw6.9 Yushu earthquake that occurred in the Chinese Mainland. By doing so, We can make a clearer picture of the stress triggering process among earthquakes, the refined spatiotemporal evolution of crustal stress field and the communication among seismogenic fault networks during different phases of earthquake cycle. Moreover, We can quantitatively track the spatiotemporal pattern of the likelihoods of earthquake hazards in those regions around strong earthquakes, and further delineate those places with high potential earthquake hazards. Besides, Our results would be also beneficial to the near real-time assessment of aftershocks evolution and to the government's scientific decision on prevention and mitigation of potential seismic risk in the future. .Above all,performing this study is undoubtedly essential to not only deepen our understanding of nucleating and rupturing of earthquake but also to help improve government's performance of the management of earthquake disaster prevention and mitigation in practice.

应力转移主要研究地震断层的力学驱动机制。本课题旨在通过对应力转移的研究，发展地壳应力场时空特征分离算法，建立顾及岩石孔隙压力时变特性和地球球体分层的地壳应力场模型、库仑应力误差估计随机模型及地震概率预测库仑应力物理模型，以构建适于整个地震周期的同震、震间及震后应力转移的理论框架。并以2008年Mw7.9汶川地震、2008年Mw7.1于田地震及2010年Mw6.9玉树地震为例，在此理论框架下具体研究地震周期中的地壳应力场与地震间的应力触发响应机制，以明确地震间的相继触发过程、地壳应力场的时空演化特征及地震断层网络的相互作用机理，定量追踪强震周边区域地震危险性时空分布，定位未来潜在地震发生段，同时也为我国未来其他大陆强震震后灾害趋势的快速评估和防灾减灾提供重要的定量科学决策方法支撑。本课题的研究对地震孕育、发生和致灾机理具有重要的科学意义，同时也对地震防灾减灾具有重要的现实意义。

本项目旨在利用库仑应力技术研究地震激发的库仑应力变化，分析强震序列同震震间和震后应力转移过程。其主要研究内容包括库仑应力误差估计模型的建立、高精度时变地壳形变场建模和强震序列应力转移分析。在库仑应力误差估计模型方面建立了一整套用于库仑应力精度分析公式，以2008年汶川地震为例定量研究了发震断层滑动分布、接收断层走向、倾角、滑动角、摩擦系数和Skempton系数误差对库仑应力的影响，发现接收断层倾角误差对库仑应力的影响甚大，而其他库仑应力模型参数误差也不可忽略，库仑应力分析应顾及这些模型参数的影响。在高精度时变地壳形变场建模方面采用张量分析工具发展了球面最小二乘配置理论，并将其应用到青藏高原主要活动断层震间构造应力加载和巴颜喀拉块体周缘强震序列的震间构造应力累积评估方面，发现鲜水河断裂震间构造应力加载率达~ 0.07 bar/yr，~40%的主要活动断层最大构造应力加载率为0.02 bar/yr，巴颜喀拉块体周缘强震的发生主要受控于块体运动所致的震间构造应力积累。本项目也研究了球体位错和弹性半空间位错理论对库仑应力的影响，发现在断层周围200 km内库仑应力空间分布大致相同，但相对量有所不同，且采用球体位错理论计算的库仑应力空间分布与展开的球谐函数阶数相关。因此采用球体位错理论进行同震库仑应力计算需顾及其数值计算精度和球谐阶数对库仑应力的影响，同时也表明区域库仑应力分析忽略地球曲率的影响是合理的。本项目提出了采用三角位错单元构建可弯曲的断层几何模型并以2010年玉树地震为例进行了断层滑动分布反演，发现震源东南侧洛荣达附件近地表滑动量最大达1.6 m。