The eastern North American margin has experienced a wide array of plate-scale tectonic deformational events, including the breakup of Pangaea. The margin may also host complex patterns of active asthenospheric mantle dynamics. Several studies have observed a strong change in anisotropy across the margin that have been interpreted variously as active asthenospheric flow or past lithospheric deformation. Separating these candidate processes has proven difficult. To constrain the likely source of the change in anisotropy across the margin, we examine scattered quasi-Love waves over three frequency ranges with peak sensitivities in the lithosphere (∼75 km), the uppermost mantle (∼150 km), and the asthenosphere (∼250 km). We observe strong quasi-Love wave scattering along the margin in the lowest two frequency bands but far fewer scatterers in the lithosphere-dominated highest frequency band. The clear frequency dependence suggests a change in anisotropy across the margin is likely located in the asthenosphere and related to active mantle dynamics.

中文翻译：

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沿北美东部边缘的岩石圈和软流圈各向异性梯度由频率相关的准洛夫波散射成像


北美东部边缘经历了一系列板块规模的构造变形事件，包括盘古大陆的分裂。该边缘还可能存在活跃的软流圈地幔动力学的复杂模式。一些研究观察到边缘各向异性的强烈变化，这些变化被不同地解释为活跃的软流圈流动或过去的岩石圈变形。事实证明，分离这些候选进程很困难。为了限制边缘各向异性变化的可能来源，我们检查了三个频率范围内的散射准洛夫波，其峰值灵敏度位于岩石圈（~75 km）、最上地幔（~150 km）和软流圈（~150 km）。 ∼250 公里）。我们在最低两个频段沿边缘观察到强烈的准洛夫波散射，但在岩石圈主导的最高频段中散射体要少得多。明显的频率依赖性表明边缘各向异性的变化可能位于软流圈中，并且与活跃的地幔动力学有关。