Characterizing geologic formations near geothermal wells is crucial for efficient extraction of subsurface geothermal energy resources. To monitor effective fracture stimulation of enhanced geothermal systems (EGS), we analyze a catalog of induced microearthquakes to characterize seismicity induced by Phase 2C fracture stimulations of the Utah FORGE project and derive the b-values for 424 induced microearthquakes in three stages of fracture stimulation. We find the time-lapse variations of these b-values. We apply eigenvector rotation and waveform correlation to 3C geophone data to separate fast S and slow S waves, determine their directions, measure their lag time, and calculate the S-wave splitting rate (SSR) for six induced microearthquakes in Stage 1 and 21 in Stage 3. Both SSR values and b-values increase with time. The increase in these values may be related to heavily fractured zones created by fracture stimulations during Stage 2 injections. Large and highly variable SSR values in Stage 3 may reflect heterogeneities in the fracture zones. Time-lapse variations of SSR values and b-values may be one of the most useful approaches to monitoring and characterizing the effectiveness and efficiency of various types of fracture stimulations.

中文翻译：

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犹他州 FORGE 的 EGS 裂缝刺激地震监测（第 1 部分）：诱发微地震的 b 值和剪切波分裂率的时移变化

表征地热井附近的地质构造对于有效开采地下地热能源至关重要。为了监测增强型地热系统 (EGS) 的有效裂缝刺激，我们分析了诱发微地震的目录，以表征犹他州 FORGE 项目 2C 阶段裂缝刺激诱发的地震活动，并推导出裂缝刺激三个阶段中 424 次诱发微地震的 b 值。我们发现这些 b 值随时间推移的变化。我们将特征向量旋转和波形相关应用于 3C 地震检波器数据，以分离快 S 波和慢 S 波，确定它们的方向，测量它们的滞后时间，并计算第 1 阶段和第 21 阶段的 6 次诱发微地震的 S 波分裂率 (SSR)。第 3 阶段。SSR 值和 b 值均随时间增加。这些值的增加可能与第二阶段注入期间裂缝增产所产生的严重裂缝区域有关。第 3 阶段中较大且高度可变的 SSR 值可能反映了断裂带的非均质性。 SSR 值和 b 值的时移变化可能是监测和表征各种类型裂缝刺激的有效性和效率的最有用的方法之一。