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历史上多数定量地震学的分析是以地震由剪切断裂引起这一假设为根据的,这样其各向同性介质中的等效力系是一对无扭矩的力偶(“双力偶”即 DC)。然而,现在高质量和高覆盖的观测资料使人们能分辨出许多地震与双力偶模型有偏离,发现一些地震,特别是在火山地区和地热区域的地震,有很强的非双力偶机制。了解非双力偶地震对于仔细研究断裂过程和辨别在某些地震中明显发生的非剪切断裂过程都是重要的。本文总结了等效力系的“矩张量”展开理论,并分析了多个非双力偶地震可能的物理过程。与长期存在的假设相反,地球中的源有时候具有有效力和扭矩分量(用一阶和不对称二阶矩张量描述),在滑坡和某些火山现象分析中必须包含这些分量。这样就导致常规(对称二阶)矩张量的非双力偶过程包括几何上复杂的剪切断裂、张性断裂、各向异性介质中的剪切断裂、非均匀区域(例如界面附近)的剪切断裂和多型相交。无疑,许多非双力偶地震过程仍有待发现。避开像无体积变化或不同矩张量分量的时间相似性这样的任意假设,利用波振幅、振幅比、全波分析等除波的极性以外的实验研究,将有利于研究的进展。
Historically, most quantitative seismological analyzes have been based on the assumption that earthquakes are caused by shear fractures so that the equivalent force in their isotropic medium is a pair of torque-free couplers (“dual couple” or DC). Now, however, high-quality and high-coverage observations make it possible to discern many earthquakes from deviating from the dual couple model and find that some earthquakes, especially those in volcanic and geothermal regions, have strong non-duality mechanisms. Understanding non-dual-couple earthquakes is important for a careful study of the fracture process and for identifying non-shear fracture processes that are evident in some earthquakes. This paper summarizes the “moment tensor” expansion theory of the equivalent force system and analyzes the possible physical processes of several non-dual-force earthquakes. Contrary to long-standing assumptions, sources in Earth sometimes have effective and torque components (described by first-order and asymmetric second-moment tensors) that must be included in landslides and some volcanic phenomena. This leads to non-dual processes of conventional (symmetric second-order) moment tensors including geometrically complex shear fractures, tensile fractures, shear fractures in anisotropic media, shear in non-uniform regions (eg near the interface) Cut fractures and polygamy intersect. Undoubtedly, many non-dual-force earthquakes still to be discovered. Avoiding any assumption such as the temporal similarity of no-volume change or different moment tensor components, the experimental study using wave amplitude, amplitude ratio, full wave analysis other than the polarity of the wave will be beneficial to the research progress.