Probing the Western Antarctic Lithosphere and Asthenosphere with New Approaches to Imaging Seismic Wave Attenuation and Velocity

南极大陆的西部板块构造过程非常活跃，可以产生地球地幔温度的显着变化以及地幔的部分熔融。 除了这些内部过程外，南极洲西部的冰盖正在融化，这是由于地球气候变暖和海洋增加了水。 这些冰量的变化导致地壳内岩石的调整，使地表在某些地方反弹，在另一些地方下降，改变了海平面变化的地理模式。 然而，固体地球的反应强烈地依赖于岩石的强度，在很宽的时间尺度范围内，这是不为人所知的，并随着温度和其他岩石性质的变化。 该项目有三个主要目标。 (1)它将评估裂谷、地幔上涌和岩石圈不稳定等过程如何改变了南极洲西部的岩石圈和下面的软流圈，从而有助于在全球范围内了解这些过程。 (2)它将使用对地幔和地壳特性的新测量来估计固体地球热量流入冰底部的速率，这对于模拟冰融化和流动的速率非常重要。 (3)它将限制地幔粘度，这是模拟固体地球与变化的冰和水质量及其对海平面上升的影响的相互作用的关键。 为了实现这些目标，将通过分析南极洲许多地震台站记录的远震地震波来获得地壳和地幔结构的新分辨率。 这些分析将包括地震波数据的新组合，提供有关地幔温度、热流和粘度的补充信息。该项目将提供教育和就业机会，布朗大学的研究生，本科生从群体在科学谁将来到布朗大学的夏季研究计划，和其他本科生代表。该项目将汇集教师和学生在布朗的研讨会，探讨固体地球和南极洲冰过程之间的联系。 项目研究将纳入对当地公立小学和高中的宣传。这项研究解决了有关南极洲西部地幔过程和性质的关键问题。 裂谷作用、地幔柱和岩石圈拆沉作用在岩石圈和软流圈演化中的相对影响是什么？ 地形均衡补偿在哪里，动力学过程如板块挠曲或三维地幔流的牵引在哪里？热流和地幔粘度的界限是什么？它们代表了冰盖演化模型的重要输入及其来自固体地球的反馈。为了解决这些问题，本项目将使用尚未在南极使用的地震工具测量地幔和地壳特性：区域尺度测量面波的地幔衰减; Sp体波相位，以成像地幔速度梯度，如岩石圈-软流圈边界;以及面波放大和椭圆率。 由此产生的地震衰减和速度的模型将共同解释，以揭示新的光的温度，整体成分，挥发分含量，和部分熔融，使用一系列的实验室衍生的本构关系，同时考虑数据从地幔捕虏体。为了测试裂谷，地幔柱和分层的相对作用，并评估南极地形的均衡支持，这些过程的预测将进行比较，地壳和地幔特性的新模型。 为了改善南极洲西部热流的界限，地震衰减和速度将用于经验比较和垂直温度梯度的直接建模。为了更好地测量冰川均衡调整时间尺度上的地幔粘度，将根据推断的地幔条件估计频率依赖的粘度。该项目将有助于以下人员的教育和职业发展：布朗大学博士。学生，布朗大学本科生和大学外的本科生将通过地球，环境和行星科学系（DEEPS）领导联盟NSF本科生研究经验（REU）网站参与，该网站专注于为代表性不足的学生提供地球科学夏季研究经验。该项目将成为布朗大学一个研讨会的基础，该研讨会将探讨南极洲固体地球和冰冻圈之间的联系，并将有助于在当地公立小学和高中的推广。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

The western portion of the Antarctic continent is very active in terms of plate tectonic processes that can produce significant variations in the Earths mantle temperature as well as partial melting of the mantle. In addition to these internal processes, the ice sheet in western Antarctica is melting due to Earths warming climate and adding water to the ocean. These changes in ice mass cause adjustments in rocks within the Earth's crust, allowing the surface to rebound in some locations and fall in others, altering the geographical pattern of sea-level change. However, the solid Earth response depends strongly on the strength of the rocks at a wide range of timescales which is not well-known and varies with temperature and other rock properties. This project has three primary goals. (1) It will assess how processes such as rifting, mantle upwelling and lithospheric instability have altered the lithosphere and underlying asthenosphere of western Antarctica, contributing to a planet-wide understanding of these processes. (2) It will use new measurements of mantle and crust properties to estimate the rate at which heat from the solid Earth flows into the base of the ice, which is important for modeling the rates at which the ice melts and flows. (3) It will places bounds on mantle viscosity, which is key for modeling the interaction of the solid Earth with changing ice and water masses and their implications for sea-level rise. To accomplish these goals, new resolution of crust and mantle structure will be obtained by analyzing seismic waves from distant earthquakes that have been recorded at numerous seismic stations in Antarctica. These analyses will include new combinations of seismic wave data that provide complementary information about mantle temperature, heat flow and viscosity. This project will provide educational and career opportunities to a Brown University graduate student, undergraduates from groups underrepresented in science who will come to Brown University for a summer research program, and other undergraduates. The project will bring together faculty and students for a seminar at Brown that explores the connections between the solid Earth and ice processes in Antarctica. Project research will be incorporated in outreach to local public elementary schools and high schools. This research addresses key questions about mantle processes and properties in western Antarctica. What are the relative impacts of rifting, mantle plumes, and lithospheric delamination in the evolution of the lithosphere and asthenosphere? Where is topography isostatically compensated, and where are dynamic processes such as plate flexure or tractions from 3-D mantle flow required? What are the bounds on heat flow and mantle viscosity, which represent important inputs to models of ice sheet evolution and its feedback from the solid Earth? To address these questions, this project will measure mantle and crust properties using seismic tools that have not yet been applied in Antarctica: regional-scale measurement of mantle attenuation from surface waves; Sp body wave phases to image mantle velocity gradients such as the lithosphere-asthenosphere boundary; and surface wave amplification and ellipticity. The resulting models of seismic attenuation and velocity will be jointly interpreted to shed new light on temperature, bulk composition, volatile content, and partial melt, using a range of laboratory-derived constitutive laws, while considering data from mantle xenoliths. To test the relative roles of rifting, mantle plumes, and delamination, and to assess isostatic support for Antarctic topography, the predictions of these processes will be compared to the new models of crust and mantle properties. To improve bounds on western Antarctic heat flow, seismic attenuation and velocity will be used in empirical comparisons and in direct modeling of vertical temperature gradients. To better measure mantle viscosity at the timescales of glacial isostatic adjustment, frequency-dependent viscosity will be estimated from the inferred mantle conditions. This project will contribute to the education and career development of the following: a Brown University Ph.D. student, Brown undergraduates, and undergraduates from outside the university will be involved through the Department of Earth, Environmental and Planetary Sciences (DEEPS) Leadership Alliance NSF Research Experience for Undergraduates (REU) Site which focuses on geoscience summer research experiences for underrepresented students. The project will be the basis for a seminar at Brown that explores the connections between the solid Earth and cryosphere in Antarctica and will contribute to outreach in local public elementary and high schools.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.