Seismic wave speed is controlled by a number of factors, including temperature and chemical composition, as well as the presence of volatiles and partial melt. Tomography provides a powerful constraint on wave speed variations, but if only V_P or V_S variations are imaged, it is challenging to separate the competing effects of these factors and make a full interpretation of seismic anomalies. In this study, we generate models of variations in the V_P/V_S ratio, which introduce new constraints on geologic structures, compositions, and processes. We invert P and S wave arrival times, as well as Rayleigh wave phase velocities, utilizing the sensitivity of Rayleigh waves to both V_P and V_S to form mutually constrained but independent models of V_P and V_S structure at lithospheric depths below the continental United States and Southeastern Canada. From this we can examine variations in V_P/V_S, highlighting a distinct pattern of anomalies which are less readily observed in V_P or V_S alone. A clustering analysis is performed to relate 1‐D profiles of wave speed as a function of depth to tectonic provinces. While the first‐order structure of V_P and V_S appears to be dominated by the thermal contrast between the Eastern and Western United States, the strongest control over V_P/V_S ratio perturbations within the mantle lithosphere appears to be the presence of melt. Certain higher‐V_P/V_S anomalies within the cratonic interior may reflect compositional anomalies and variations in Moho structure. This work provides a continental‐scale framework for future quantitative analyses of thermal and compositional heterogeneity, and for targeted geologic interpretation.

中文翻译：

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北美岩石圈地震波速度和VP / VS比的变化

地震波速度受许多因素控制，包括温度和化学成分，以及挥发物和部分熔体的存在。层析成像技术对波速变化提供了强大的约束条件，但是如果仅对V _P或V _S变化成像，则将这些因素的竞争效应分开并完整解释地震异常将是一项挑战。在这项研究中，我们生成了V _P / V _S比变化的模型，这些模型引入了对地质结构，组成和过程的新约束。我们反转P和S波的到达时间以及瑞利波的相位速度，利用瑞利波对V _P和V _S的敏感度，在美国大陆和加拿大东南部以下的岩石圈深度处形成相互约束但独立的V _P和V _S结构模型。由此，我们可以检查V _P / V _S的变化，突出显示出异常模式，这种异常模式在V _P或V _S中不易观察到。单独。进行聚类分析以将一维波速剖面作为深度函数与构造省份相关联。尽管V _P和V _S的一阶结构似乎受美国东部和西部之间的热对比所支配，但对地幔岩石圈内V _P / V _S比扰动的最强控制似乎是存在熔体。某些较高的V _P / V _S克拉通内部的异常可能反映了莫霍面的成分异常和变化。这项工作为未来的热和成分非均质性定量分析以及有针对性的地质解释提供了一个大陆尺度的框架。