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

就板块构造过程而言，南极大陆西部非常活跃，这可能导致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，南极西部的冰盖正在融化，原因是地球使气候变暖，并向海洋增加了水。冰块的这些变化导致地壳内岩石的调整，使地表在一些地方反弹，在另一些地方下降，改变了海平面变化的地理格局。然而，固体地球的响应在很大程度上取决于岩石在广泛的时间范围内的强度，这一点并不为人所知，而且随着温度和其他岩石性质的变化而变化。这个项目有三个主要目标。(1)它将评估裂谷作用、地幔上涌和岩石圈不稳定等过程如何改变了南极西部的岩石圈和底层软流圈，有助于在全地球范围内了解这些过程。(2)它将使用地幔和地壳性质的新测量来估计来自固体地球的热量流入冰底部的速度，这对于模拟冰融化和流动的速度很重要。(3)它将设定地幔粘度的界限，这是模拟固体地球与变化的冰和水团的相互作用及其对海平面上升的影响的关键。为了实现这些目标，将通过分析南极多个地震台记录的远距离地震的地震波，获得新的地壳和地幔结构分辨率。这些分析将包括地震波数据的新组合，这些数据提供关于地幔温度、热流和粘度的补充信息。该项目将为布朗大学的研究生、来自科学方面代表性不足的团体的本科生来布朗大学进行暑期研究项目的本科生以及其他本科生提供教育和职业机会。该项目将在布朗大学举行一次研讨会，探讨固体地球和南极洲冰川过程之间的联系。项目研究将纳入到当地公立小学和高中的外联活动中。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、地幔热柱和岩石圈拆沉在岩石圈和软流圈演化中的相对影响是什么？地形在哪里是均衡补偿的，在哪里需要动态过程，如板块弯曲或来自三维地幔流动的牵引力？热流和地幔粘度的界限是什么，它们代表着冰盖演化模型及其来自固体地球的反馈的重要输入？为解决这些问题，该项目将使用尚未在南极洲应用的地震工具来测量地幔和地壳的性质：区域尺度测量地幔表面波衰减；Sp体波相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度。由此产生的地震衰减和速度模型将被联合解释，以揭示温度、主体成分、挥发分含量和部分熔体的新情况，使用一系列实验室推导的本构关系，同时考虑来自地幔包体的数据。为了测试裂谷作用、地幔热柱和分层作用的相对作用，并评估南极地形的均衡支撑，这些过程的预测将与新的地壳和地幔性质模型进行比较。为了改善南极西部热流的界限，地震衰减和速度将用于经验比较和垂直温度梯度的直接模拟。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与频率有关的粘度。该项目将有助于以下人员的教育和职业发展：布朗大学的一名博士生、布朗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)领导力联盟NSF本科生研究经验(REU)网站参与，该网站重点关注未被充分代表的学生的地球科学暑期研究经验。该项目将成为布朗大学研讨会的基础，该研讨会将探索南极洲固体地球和冰冻层之间的联系，并将有助于当地公立小学和高中的推广。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.