The development of the Rittershoffen deep geothermal field (Alsace, Upper Rhine Graben) between 2012 and 2014 induced unfelt seismicity with a local magnitude of less than 1.6. This seismicity occurred during two types of operations: (1) mud losses in the Muschelkalk formation during the drilling of both wells of the doublet and (2) thermal and hydraulic stimulations of the GRT-1 well. Seismicity was also observed 4 days after the main hydraulic stimulation, although no specific operation was performed. During chemical stimulation, however, no induced seismicity was detected. In the context of all field development operations and their injection parameters (flow rates, overpressures, volumes), we detail the occurrence or lack of seismicity, its magnitude distribution and its spatial distribution. The observations suggest the presence of the rock stress memory effect (Kaiser effect) of the geothermal reservoir as well as uncritically stressed zones connected to the GRT-1 well and/or rock cohesion. A reduction of the seismic rate concurrent with an increase of injectivity was noticed as well as the reactivation of a couple of faults, including the Rittershoffen fault, which was targeted by the wells. These results are derived from the homogeneous and consistent catalogue of more than 1300 local earthquakes that is provided. This reference catalogue is based on a standard detection method, whose output was manually verified and improved. The given absolute locations have been computed in a calibrated, geologically realistic 3D velocity model. Our work builds on previous analyses addressing the seismicity induced by the GRT-1 hydraulic stimulation and places the results into a historical context, thus considering the full dynamics of the observed phenomena. This paper also complements existing descriptions of the hydrothermal characteristics of the deep reservoir by providing insights separate from the wells.

中文翻译：

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法国Rittershoffen地热田开发过程中引起的地震作用

2012年至2014年期间，Rittershoffen深层地热田（阿尔萨斯，上莱茵大学格拉本）的发展引起了毛毡地震，局部震级小于1.6。这种地震活动发生在两种类型的作业中：（1）在双重井的两个井的钻探过程中，Muschelkalk地层中的泥浆流失；（2）GRT-1井的热力和水力增产。主液压刺激后第4天也观察到了地震，尽管没有进行任何特定的操作。但是，在化学刺激过程中，未检测到诱发地震。在所有现场开发作业及其注入参数（流速，超压，体积）的背景下，我们详细介绍了地震活动的发生与否，震级分布及其空间分布。观测结果表明，存在地热储层的岩石应力记忆效应（Kaiser效应）以及与GRT-1井和/或岩石凝聚力相关的非临界应力带。注意到地震速率的降低和注入量的增加，以及几个断层的重新激活，包括Rittershoffen断层，这些断层是井的目标。这些结果来自提供的1300多次本地地震的一致且一致的目录。此参考目录基于标准检测方法，其输出已手动验证和改进。给定的绝对位置已在经过校准的，地质上逼真的3D速度模型中进行了计算。我们的工作建立在先前针对GRT-1水力刺激引起的地震活动的分析基础上，并将结果置于历史背景下，从而考虑了所观察到的现象的全部动态。本文还通过提供与井分开的见解来补充对深层储层热液特征的现有描述。