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的。该大陆的西半部包括一个主要的板块边界，并在最近的地质历史中经历了造山活动，火山活动和延伸。北美洲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产生这种复杂的地形，对于了解大陆的生长和演变，特别是北美大陆的生长和演变至关重要。通过地壳和地幔传播的地震波速度的成像变化提供了对这些地区的温度和成分以及部分熔融岩石存在的重要限制。然而，由于这些因素中的每一个以及它们的任何组合都可能影响速度，因此需要额外的数据集来实现可靠的解释。 地震波能量的吸收也受到温度、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，对北美地下地震衰减的研究很少，主要是因为测量和分析地震波振幅的困难。研究员将利用USAray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。面波相位和振幅的测量采用了新的台站间互相关方法，该方法利用了附近台站的波形相似性，相位和振幅数据将一起使用，以利用两个数据集对地震速度和衰减的依赖性。从这些模型中，可以估计整个大陆的温度、成分和部分熔融的变化，并可以更完整地了解科罗拉多高原、盆地和山脉、中大陆裂谷和北美克拉通等结构是如何受到下伏地幔的过程和性质的控制的。

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.