Gravity measurements in the Upper Rhine Graben evidence spatial variations at the regional scale and close to the geothermal sites. They are classically interpreted as linked to the geology. We aim to bring new insights on another potential origin of these gravity changes. Our approach is to quantify gravity anomalies related to the deep hydrothermal circulation. A thermo-hydro-mechanical model is developed at the reservoir scale for the Soultz-sous-Forêts site (Soultz), France. A finite element method is used in 2D and 3D. The size of the representative elementary volume is assumed to be 100 m with no regional fault in the reservoir. Surface gravity profiles and maps associated to the large-scale hydrothermal circulation are computed from the variations of the effective density through the model. Synthetic spatial gravity variations in 2D and 3D models are shown to have an amplitude of 0.02 mGal. They are shown to be mostly linked to the convective system. Their wavelength is about 7.5 km, consistent with the width of the hydrothermal convection cells. The anomaly maximum is located at the top of the maximum surface heat flux. However, gravity anomaly observations show much higher amplitude and heterogeneity. Spatial gravity variations linked to the hydrothermal circulation are shown to be smaller than the observed gravity spatial variations, but still measurable with very sensitive instruments (absolute gravimeters).

中文翻译：

---

与Soultz-sous-Forêts（法国）的深部热液循环有关的重力异常的THM建模

上莱茵河格拉本上的重力测量结果表明，该区域在区域范围内且靠近地热站都有空间变化。传统上将它们解释为与地质联系在一起。我们旨在为这些引力变化的另一个潜在来源带来新的见解。我们的方法是量化与深部热液循环有关的重力异常。在法国Soultz-sous-Forêts站点（Soultz）的储层范围内开发了热-水力-力学模型。在2D和3D中使用有限元方法。假设基本储集层的大小为100 m，储层中无区域性断层。通过模型从有效密度的变化中计算出与大规模水热循环有关的表面重力剖面和图。2D和3D模型中的合成空间重力变化显示为0.02 mGal。它们显示出主要与对流系统有关。它们的波长约为7.5 km，与水热对流池的宽度一致。异常最大值位于最大表面热通量的顶部。但是，重力异常观测结果显示出更高的幅度和非均质性。与水热循环有关的空间重力变化显示为小于观测到的重力空间变化，但仍可以使用非常灵敏的仪器（绝对重力仪）进行测量。异常最大值位于最大表面热通量的顶部。但是，重力异常观测结果显示出更高的幅度和非均质性。与水热循环有关的空间重力变化显示为小于观测到的重力空间变化，但仍可以使用非常灵敏的仪器（绝对重力仪）进行测量。异常最大值位于最大表面热通量的顶部。但是，重力异常观测结果显示出更高的幅度和非均质性。与水热循环有关的空间重力变化显示为小于观测到的重力空间变化，但仍可以使用非常灵敏的仪器（绝对重力仪）进行测量。