One of the key goals of microseismic processing is accurate estimation of the source location. Using full-waveform information in passive-source data sets can potentially delineate microseismic sources. The accuracy of the compressional-wave and shear-wave velocities has a strong influence on the estimation of source locations and hence the reliability of the fracture detection. We have adopted a methodology for passive source and velocity inversion, in which the conventional source term of the elastic wave equation is represented by an equivalent source. The equivalent source term is composed of source images and source functions because it is inspired by elastic reflection waveform inversion. Thus, we update the source locations, source functions, and velocities simultaneously by using a waveform inversion scheme. In the 2D isotropic case, the source terms are defined by two source image components and three source function components. They provide an alternative representation of the source mechanism, usually defined by the moment tensor. Waveform inversion of passive events has severe nonlinearity due to the unknown source locations in space and their functions in time. We have thus used a source-independent objective function, based on convolving reference traces with modeled and observed data, to avoid cycle skipping caused by the unknown sources. We first synthetically examined our method on a modified Marmousi model. Then, by applying a nested inversion for these variables, our method also produces good estimation of the source and background velocity for real microseismic monitoring data. We use a ball-drop event to test the accuracy because the inverted source location should match the ball-seat location. For the uncontrolled events, the estimated source distribution using waveform inversion agrees with the local stress potential information. Although our method has a higher computational cost than traveltime- or migration-based methods, the estimated event locations have significantly improved accuracy.

中文翻译：

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具有全波形反演的正则弹性无源等效源反演：在现场监测微地震数据集中的应用

微震处理的主要目标之一是精确估算震源位置。在被动源数据集中使用全波形信息可能会勾勒出微震源。压缩波和剪切波速度的准确性对震源位置的估计有很大的影响，因此对裂缝检测的可靠性也有很大的影响。我们采用了一种用于被动源和速度反演的方法，其中，弹性波方程的常规源项由等效源表示。等效源项由源图像和源函数组成，因为它受弹性反射波形反演的启发。因此，我们通过使用波形反转方案同时更新了源位置，源函数和速度。在二维各向同性的情况下，源术语由两个源图像组件和三个源功能组件定义。它们提供了通常由力矩张量定义的源机制的替代表示。由于未知的空间源位置及其时间功能，被动事件的波形反转具有严重的非线性。因此，我们基于与模型和观测数据卷积的参考迹线使用了与源无关的目标函数，以避免由未知源引起的周期跳跃。我们首先在改进的Marmousi模型上综合检查了我们的方法。然后，通过对这些变量应用嵌套反演，我们的方法还可以对真实的微震监测数据的源速度和背景速度进行良好的估计。我们使用落球事件来测试准确性，因为倒置的源位置应该与球座位置匹配。对于不受控制的事件，使用波形反演的估计震源分布与局部应力势信息一致。尽管我们的方法比基于旅行时间或迁移的方法具有更高的计算成本，但是估计的事件位置具有显着提高的准确性。