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使用离散刚性块体模型为单个滑动事件和多个滑动事件的平均值定义了非对称矩张量,用来说明颗粒介质的脆性变形。对于脆性地壳,颗粒被视为断层边界的块体。经过数次滑动事件,永久变形在块体的边界上积累。用两个独立运动来描述变形:块体矩心的局部相对运动和块体围绕自身矩心的局部刚性旋转。取一个体积内多个滑动事件的每个局部运动的平均值,将其定义为宏观变形和微旋转,其中宏观变形包括宏观应变和宏观旋转。分别由局部和平均运动定义不对称局部微极矩张量和不对称微极矩密度张量。本文提出的模型说明:(1)微极矩张量的对称部分取决于块体矩心的定容局部剪切应变或其平均当量——宏观应变;(2)反对称部分取决于被定义的客观量,像与矩心变形有关的旋转分量和局部块体旋转之间的差分,或者它们的平均当量宏观旋转和微旋转;(3)使用标准地震震源机制的微极反演,可以推断出微极矩密度张量的对称和反对称部分的标量幅度。3个区域的检验结果说明了与理论的一致性,但是确定性的检验仍然受到定量信息不充分或数据的分辨率不足等因素的限制。
An asymmetric moment tensor is defined for a single sliding event and an average of multiple sliding events using a discrete rigid block model to account for the brittle deformation of the granular media. For brittle crust, the particles are considered as blocks of fault boundaries. After several sliding events, permanent deformation accumulates on the boundary of the block. Two independent movements are used to describe the deformation: the local relative motion of the centroid of the block and the local rigid rotation of the block around its own centroid. The average of each local motion of multiple slip events within a volume is defined as macro-deformation and micro-rotation, where macro-deformation includes macro-strain and macro-rotation. The local and average motions are used to define the asymmetric local micropolar moment tensor and the asymmetric micropolar moment density tensor, respectively. The model presented in this paper shows that: (1) the symmetry of the microtext moment tensor depends on the constant volume local shear strain of the centroid of the mass or its average equivalent-macroscopic strain; (2) the antisymmetry depends partly on the defined Objectives, such as the difference between the rotation component associated with the centroid deformation and the rotation of the local mass, or their average equivalent macro-rotation and micro-rotation; (3) Using the micropolar inversion of a standard seismic focal mechanism, one can deduce Scalar Magnitude of the Symmetric and Antisymmetric Parts of the Minimal Moment Density. The test results in the three regions illustrate the consistency with the theory, but deterministic tests are still limited by insufficient quantitative information or inadequate resolution of the data.