Collaborative Research: Investigating Temperature, Melting, and Mantle Flow in the North American Upper Mantle with 3-D Models of Shear Velocity, Radial Anisotropy, and Attenuation

北美大陆在地质和构造上是多样化的。大陆的西半部包括一个主要的板块边界，在最近的地质历史中曾发生过造山事件、火山活动和扩张。北美东部远离任何板块边界，数亿年来没有经历过重大的构造活动。了解地球内部发生的动态过程如何形成这种复杂的地形，对于了解整个大陆，特别是北美的增长和演变是至关重要的。对穿过地壳和地幔的地震波传播速度的变化进行成像，对这些地区的温度和成分以及部分熔岩的存在提供了重要的限制。然而，由于这些因素中的每一个以及它们的任何组合都会影响速度，因此需要更多的数据集来实现稳健的解释。地震波能量的吸收也受温度、成分和熔体含量的控制，因此联合解释地震波速度和衰减的变化可以改善对地球内部性质的约束。到目前为止，关于北美以下地震衰减的研究很少，这主要是因为测量和分析地震波的幅度涉及到困难。PI将利用USArray记录的面波建立北美上地幔剪切衰减和径向各向异性剪切速度的三维模型。面波的相位和幅度是用一种新的台间互相关法测量的，这种方法利用了附近台站的波形相似性，并将相位和幅度数据一起利用，以利用两个数据集对地震速度和衰减的依赖性。通过这些模型，将估计整个大陆的温度、成分和部分熔融的变化，并将出现科罗拉多高原、盆地和山脉、中大陆裂谷和北美克拉通等结构如何受下伏地幔的过程和性质控制的更完整的图景。

The continent of North America is geologically and tectonically diverse. The western half of the continent includes a major plate boundary and has been host to mountain-building events, volcanism, and extension within the recent geological past. The eastern portion of North America is located far from any plate boundary and has not experienced significant tectonic activity in hundreds of millions of years. Understanding how the dynamic processes occurring in Earth's interior have given rise to this complex terrain is fundamental to understanding the growth and evolution of continents in general and North America in particular. Imaging variations in the speed of seismic waves traveling through the crust and mantle provides important constraints on the temperature and composition of those regions as well as the presence of partially molten rock. However, since each of these factors, and any combination of them, can affect velocity, additional data sets are needed to achieve a robust interpretation. The absorption of seismic-wave energy is also controlled by temperature, composition, and melt content, and thus jointly interpreting variations in seismic-wave velocity and attenuation allows for improved constraints on the properties of Earth's interior. To date, there have been very few studies of seismic attenuation beneath North America, largely because of the difficulties involved with measuring and analyzing the amplitudes of seismic waves. The PIs will develop 3-D models of shear attenuation and radially anisotropic shear velocity for the North American upper mantle using surface waves recorded by USArray. Surface-wave phase and amplitude are measured using a new interstation cross-correlation approach that exploits waveform similarity at nearby stations, and the phase and amplitude data will be utilized together to take advantage of the dependence of both data sets on seismic velocity and attenuation. From these models, variations in temperature, composition, and partial melt across the continent will be estimated, and a more complete picture of how structures like the Colorado Plateau, the Basin and Range, the Mid-Continent Rift, and the North American craton are controlled by the processes in and properties of the underlying mantle will emerge.