Fluids on faults facilitate triggering of earthquakes and affect seismic energy release. Their detection in the focal zone is, however, difficult. Here, we present mapping of stress changes and fluid flow based on determining seismic moment tensors (MTs), which describe focal mechanisms and shear/tensile/compressive fracturing modes of earthquake sources. We calculate highly accurate MTs of 4,500 microearthquakes that occurred in the West Bohemia swarm region in the period of 2008–2018. The extent and quality of the moment tensor data are unique and allow us to study detailed behavior of the nondouble‐couple (nonDC) components of MTs along the fault. The nonDC components were mostly zero or negative and indicated shear/compressive fracturing. However, also a patch with positive nonDC components, indicating tensile fracturing, was revealed. The inversion for stress and modeling of the Coulomb stress change confirmed that this patch is under anomalous stress conditions. Tensile fractures in the patch were opened due to interaction of tensile fault steps and filled by overpressurized fluids. Hence, evaluating nonDC components of earthquakes might help for tracing stress variations and fault interactions, identifying pathways of fluids and locating areas with overpressure prone to being activated.

中文翻译：

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通过非剪切地震将应力和流体映射到断层上

断层上的流体有助于触发地震并影响地震能量释放。但是，很难在焦点区域对其进行检测。在这里，我们根据确定的地震矩张量（MT）提出应力变化和流体流动的映射，该矩量张量描述了震源的震源机理和剪切/拉伸/压缩断裂模式。我们计算出在2008-2018年期间发生在西波西米亚群地区的4,500场微地震的高精度MT。矩张量数据的范围和质量是独一无二的，这使我们能够研究沿断层MT的非双耦合（nonDC）分量的详细行为。非DC成分大部分为零或负，表示剪切/压缩断裂。但是，还发现了带有正性非DC成分的贴剂，表明拉伸断裂。应力的反演和库仑应力变化的模型证实了该斑块处于异常应力条件下。由于拉伸断层阶跃的相互作用，补片中的拉伸裂缝被打开，并被超压流体填充。因此，评估地震的非直流分量可能有助于追踪应力变化和断层相互作用，识别流体路径并定位容易被激活的超压区域。