We have developed an approach to determine the time-dependent moment tensor and the origin time in addition to commonly derived locations of seismic events using time reverse imaging (TRI). It is crucial to locate and characterize the occurring microseismicity without making a priori assumptions about the sources to fully understand the subsurface processes inducing seismicity. Low signal-to-noise ratios (S/Ns) often force standard methods to make assumptions about sources or only characterize selected larger magnitude events. In TRI, microearthquakes are located by back propagating the full-recorded time-reversed wavefield through a velocity model until it ideally convergences on the source location. Therefore, it is less affected by low S/Ns and potentially locates and characterizes most of the events. After distinguishing artificial convergence locations from source locations, the quality of the source location and the moment tensors are derived by recording the stress at the determined source locations during the back propagation of the time-reversed wavefield. A robust workflow is derived using synthetic test cases in a realistic scenario with velocity models that only approximate the true velocity model and/or noisy displacement traces. The influence of a rudimentary velocity model on the source-location accuracy and characterization is significant. Our workflow handles these less-than-optimal station distributions and velocity models. Finally, the derived workflow is successfully applied to field data recorded at the geothermal field of Los Humeros, Mexico. Although only a 1D velocity model is currently available, source locations and (time-dependent) moment tensors could be determined for selected events.

中文翻译：

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使用时间反向成像确定时间相关的矩张量

除了使用时间倒置成像（TRI）共同确定地震事件的位置以外，我们还开发了一种确定时间相关矩张量和起始时间的方法。在不事先对震源进行先验假设的情况下，对发生的微地震进行定位和特征化至关重要，以充分理解引起地震活动的地下过程。低信噪比（S / Ns）通常迫使标准方法对源进行假设或仅表征选定的较大幅度事件。在TRI中，通过将整个记录的时间反转波场通过速度模型反向传播，直到其在源位置理想地收敛，从而定位微地震。因此，它受低S / N的影响较小，并且有可能定位并表征大多数事件。在将人工收敛位置与源位置区分开后，通过记录时间反向波场的反向传播期间确定的源位置处的应力，可以得出源位置和矩张量的质量。在逼真的场景中使用合成测试用例，通过仅近似真实速度模型和/或嘈杂的位移轨迹的速度模型，可以得出强大的工作流程。原始速度模型对震源位置精度和特征的影响是很大的。我们的工作流处理这些次优站分布和速度模型。最后，导出的工作流程已成功应用于墨西哥Los Humeros地热场记录的现场数据。尽管目前只有一维速度模型，