The evaluation of groundwater presence by means of seismic wave velocities is of great concern for many hydrological related engineering applications. This work introduces a simple basic procedure to accurately and systematically identify groundwater levels using P-wave and S-wave velocities. This procedure is defined as a seismic reflectivity parameter and based on the seismic reflection coefficients of P-wave and S-wave at the unsaturated/saturated interfaces (i.e., groundwater level). The present procedure is applied to 1045 K-NET sites in Japan. Observed velocity structures, accompanied by their bulk densities and detailed lithology, for the upper 20 m depth are obtained from the National Research Institute for Earth Science and Disaster Prevention, Japan. Calculations are carried out considering three distinct lithological conditions – gravel, sand and clay–silt sediments – in order to evaluate the ability of this approach (seismic reflectivity parameter) to detect the groundwater level and assess its practical limitations. The increase of the seismic reflectivity parameter value varies substantially with Poisson's ratio, resembling the relationship between $V_P/V_S$ and Poisson's ratio in gravel, sand and clay–silt sediments. However, positive seismic reflectivity parameter values indicate groundwater presence, whereas negative seismic reflectivity parameter values indicate lithological variation. The seismic reflectivity parameter can also be used as a relative indicator for groundwater saturation levels. Fair comparisons are established between the seismic reflectivity parameter and the water seismic index technique. However, the seismic reflectivity parameter approach shows consistency with previous theoretical and experimental studies related to variations of $V_P$ and $V_S$ in saturated conditions, whereas the water seismic index shows inconsistency with these previous theoretical and experimental studies and an inability in determining saturation levels and detecting groundwater levels.

中文翻译：

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日本 K-NET 建议的地下水位确定方法的适用性

通过地震波速度评估地下水的存在是许多水文相关工程应用非常关注的问题。这项工作介绍了一个简单的基本程序，可以使用P波和S波速度准确和系统地识别地下水位。该程序被定义为地震反射率参数，并基于P波和S波的地震反射系数- 非饱和/饱和界面（即地下水位）的波。本程序适用于日本的 1045 个 K-NET 站点。观测到的速度结构，连同它们的体积密度和详细的岩性，从日本国家地球科学和防灾研究所获得，在上面 20 m 深度。计算考虑了三种不同的岩性条件——砾石、沙子和粘土-粉砂沉积物——以评估这种方法（地震反射率参数）检测地下水位的能力并评估其实际局限性。地震反射率参数值的增加随泊松比变化很大，类似于${伏}_{磷}/{伏}_{秒}$砾石、沙子和粘土-粉砂沉积物中的泊松比。然而，正地震反射率参数值表示存在地下水，而负地震反射率参数值表示岩性变化。地震反射率参数也可用作地下水饱和度的相对指标。在地震反射率参数和水地震指数技术之间建立了公平的比较。然而，地震反射率参数方法显示出与先前有关变化的理论和实验研究的一致性。${伏}_{磷}$ 和 ${伏}_{秒}$ 在饱和条件下，而水地震指数显示与这些先前的理论和实验研究不一致，并且无法确定饱和度和检测地下水位。