Seismological studies of cratonic lithosphere: investigating lithospheric rheology, heat flow beneath ice sheets, and the origin of mid-lithospheric discontinuities

构成海底的海洋地壳与人类赖以生存的大陆地壳有着根本的区别。大陆地壳比海洋地壳厚而轻。它的平均年龄也要大得多：最古老的海洋地壳有2亿年的历史，而最古老的大陆地壳有43亿年的历史。所有这些差异——厚度、浮力和年龄——都可以归因于地幔的性质和地幔内部发生的过程。这项研究将利用地震产生的地震波对大陆下的地幔进行成像，采用类似于对人体进行CT扫描的方法。这项研究将试图回答有关形成并随后改变大陆的事件如何赋予它们浮力和寿命的问题，这对它们的宜居性至关重要。就更广泛的影响而言，该项目将支持一名研究生和几名本科生，其中至少有一名来自STEM中代表性不足的群体。本研究将通过建立全球几个克拉通的地震衰减、速度和各向异性结构的新模型，促进对克拉通形成和改造过程的理解。为此，研究将：(1)对瑞利波衰减和各向异性相速度、Ps和Sp接收函数以及横波分裂进行同位分析；(2)利用正演和反演方法从体波和面波数据中确定剪切速度、剪切衰减和方位各向异性的深度相关模型；(3)结合地震模型、橄榄岩和含水相的弹性性质以及非弹性实验，验证岩石圈中部不连续成因的假设；(4)结合地幔-捕虏体和热流数据，建立了一种适用于冰盖地区的岩石圈热化学结构估算方法。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

There are fundamental differences between the oceanic crust that comprises the seafloor and the continental crust on which humans live. Continental crust is thicker and lighter than oceanic crust. It is also, on average, much older: the oldest oceanic crust is 200 million years whereas the oldest continental crust is 4300 million years. All of these differences—thickness, buoyancy, and age—can be attributed to the properties of and the processes occurring within the Earth’s mantle. This study will use seismic waves generated by earthquakes to image the mantle beneath continents, employing methods similar to those used to perform CT scans on the human body. The study will seek to answer questions about how the events that formed and subsequently modified the continents imbued them with their buoyancy and longevity, which are crucial to their habitability. In terms of broader impacts, the project will support one graduate student and several undergraduates, including at least one from an under-represented group in STEM. This study will advance understanding of the processes that form and modify cratons by developing new models of the seismic attenuation, velocity, and anisotropy structure at several cratons around the globe. To accomplish this, the study will: (1) perform co-located analyses of Rayleigh wave attenuation and anisotropic phase velocity, Ps and Sp receiver functions, and shear-wave splitting; (2) determine depth-dependent models of shear velocity, shear attenuation, and azimuthal anisotropy from the body- and surface-wave data using both forward and inverse approaches; (3) test hypotheses for the origin of midlithospheric discontinuities by interpreting the seismic models together with the elastic properties of peridotite and hydrous phases and with anelasticity experiments; (4) through incorporation of mantle-xenolith and heat-flow data, develop a method for estimating lithospheric thermal and chemical structure that can be applied in ice-covered regions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.