Improving our understanding of the relation between the water content and the seismic signatures of unconsolidated superficial soils is an important objective in the overall field of hydrogeophysics. Current approaches to constrain the water content in the vadose zone from seismic data are based on computing the ratio between compressional and shear wave velocities V_p/V_s. While this allows for the detection of pronounced changes in saturation, such as the groundwater table, it is essentially insensitive to variations in the saturation-depth profile. Conversely, evidence shows that surface waves are sensitive to both the location of the water table and the saturation-depth profile. Classic rock physics models are unable to explain the corresponding observations. We propose to estimate surface-wave signatures accounting for capillary suction effects. We extend the Hertz-Mindlin model using Bishop's effective stress definition, thus accounting for stiffness changes associated with capillary stresses acting on the soil's frame. We then compute the elastic properties of the partially saturated medium using the Biot-Gassmann-Wood model. Considering a 1D unconsolidated porous medium under steady-state saturation conditions, as given by Richards' equation, we simulate body-wave travel times and surface-wave dispersion characteristics for different water table depths and overlying soil textures. Our results illustrate that surface-wave phase velocity dispersion curves are remarkably sensitive to capillary effects in partially saturated soils, exhibiting velocity changes of up to 20% in the 10–100 Hz frequency range. These effects, which are particularly important in medium-to fine-grained soils, are virtually nonexistent in the corresponding V_p/V_s profiles.

中文翻译：

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部分饱和土壤中的表面波色散：毛细管力的作用

提高我们对松散表层土壤含水量与地震特征之间关系的理解是整个水文地球物理学领域的一个重要目标。当前根据地震数据限制包气带中的水含量的方法是基于计算纵波速度和横波速度V _p / V _s之间的比率. 虽然这允许检测饱和度的显着变化，例如地下水位，但它基本上对饱和度-深度剖面的变化不敏感。相反，有证据表明表面波对地下水位的位置和饱和深度剖面都很敏感。经典的岩石物理模型无法解释相应的观察结果。我们建议估计考虑到毛细管吸力效应的表面波特征。我们使用 Bishop 的有效应力定义扩展了 Hertz-Mindlin 模型，从而解释了与作用在土壤框架上的毛细应力相关的刚度变化。然后我们使用 Biot-Gassmann-Wood 模型计算部分饱和介质的弹性特性。考虑在稳态饱和条件下的一维松散多孔介质，如理查兹方程给出的那样，我们模拟了不同地下水位深度和上覆土壤质地的体波传播时间和表面波色散特性。我们的结果表明，表面波相速度频散曲线对部分饱和土壤中的毛细管效应非常敏感，在 10-100 Hz 频率范围内表现出高达 20% 的速度变化。这些影响在中到细粒土壤中尤为重要，但在相应的土壤中几乎不存在。我们的结果表明，表面波相速度频散曲线对部分饱和土壤中的毛细管效应非常敏感，在 10-100 Hz 频率范围内表现出高达 20% 的速度变化。这些影响在中到细粒土壤中尤为重要，但在相应的土壤中几乎不存在。我们的结果表明，表面波相速度频散曲线对部分饱和土壤中的毛细管效应非常敏感，在 10-100 Hz 频率范围内表现出高达 20% 的速度变化。这些影响在中到细粒土壤中尤为重要，但在相应的土壤中几乎不存在。V _p / V _s配置文件。