Using ocean tidal load response to explore upper mantle density and elastic structure

地震学已经彻底改变了我们对地球内部的理解，但它在区分地球内部不同基本特性的变化方面的能力也有限，例如弹性特性和密度之间的变化。 限制这些性质对于从根本上理解地球的演化、大陆的结构和驱动板块构造的过程至关重要。 这个项目探索使用一种新的可观测的，可以补充地震学作为地球探测器？的内部。 利用全球定位系统对地面运动的估计，人们现在可以探测到与每日潮汐有关的水团周期性运动的影响，因为它们由于移动海洋的巨大重量而弯曲地球表面。 由于弯曲的量直接由固体地球的内部属性控制，我们可以使用这些观测结果与海洋潮汐模型相结合，以限制内部属性的空间变化。 该项目的重点是开发这些新的观测类型，并将其用于地球上地幔结构的模型中，特别侧重于了解南美洲大陆地球最外500公里的地球。地球的海洋潮汐负荷（OTL）响应表现为水平和垂直空间位移，最大可达5- 1000米。振幅为10厘米，由全球定位系统接收器定期测量，精度为1毫米。 对OTL响应的调查提供了一种直接的方法来检验地震学中普遍采用的标度律和假设，以将地震速度与基本岩石性质联系起来，同时也提供了一种方法来拒绝现有的与大地测量观测不一致的地球模型。此外，推断的密度和弹性模型可以用来解决地球物理学中的突出问题，如大陆板块的长期稳定性对构造变形。这一努力的副产品将是计算基础设施的发展，在贝叶斯框架内反演潮汐观测。

Seismology has revolutionized our understanding of the Earth's interior, but is also limited in its ability to distinguish between variations in different basic characteristics inside the Earth such between elastic properties and density. Constraining such properties is essential to the fundamental understanding of the evolution of the earth, the structure of continents and the processes driving plate tectonics. This project explores the use of a new observable that can complement seismology as a probe of the earth?s interior. Using global position system (GPS) estimates of ground movement, one can now detect the impact of the periodic movement of water mass associated with daily tides as they flex the surface of the earth due to the enormous weight of the moving oceans. Since the amount of flexing is directly controlled by interior properties of the solid earth, we can use these observations coupled with models of the ocean tides to constrain spatial variations in interior properties. This project focuses on both developing these new observation types and using them in models of the structure of the Earth's upper mantle with a particular focus on understanding the outermost 500 km of the Earth in the South American continent.Earth's ocean tidal load (OTL) response is manifest as horizontal and vertical spatial displacements up to 5-10 cm in amplitude and are regularly measured by GPS receivers with 1 mm accuracy at sub-daily tidal periods. Investigations into OTL response provide a direct means of testing scaling laws and assumptions commonly adopted in seismology to relate seismic velocities to fundamental rock properties, as well as a means of rejecting existing proposed models of the Earth that are inconsistent with the geodetic observations. Furthermore, inferred density and elasticity models can be used to address outstanding questions in geophysics, such as the long-term stability of continental cratons against tectonic deformation. A byproduct of this effort will be the development of computational infrastructure to invert tidal observations in a Bayesian framework.