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

利用地震波衰减和速度成像新方法探测南极西部岩石圈和软流圈

• 批准号: 2201129
• 负责人: Karen Fischer
• 金额: $ 50.73万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-06-01 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2201129&HistoricalAwards=false
• 关键词: Probing; Western; Antarctic; Lithosphere; Asthenosphere

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.

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著变化以及地幔的部分熔融。除了这些内部过程之外，由于地球气候变暖和海水增加，南极洲西部的冰盖正在融化。这些冰块的变化引起地壳内岩石的调整，使一些地方的表面反弹，另一些地方的表面下降，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大范围时间尺度上的强度，这是未知的，并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、地幔上涌和岩石圈不稳定等过程如何改变南极洲西部的岩石圈和潜在的软流圈，有助于在全球范围内了解这些过程。它将利用对地幔和地壳性质的新测量来估计固体地球的热量流入冰底的速率，这对于模拟冰融化和流动的速率是很重要的。(3)它将确定地幔黏度的界限，这是模拟固体地球与不断变化的冰和水质量的相互作用及其对海平面上升影响的关键。为了实现这些目标，将通过分析南极许多地震台站记录的遥远地震的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、来自未被充分代表的科学群体的本科生以及其他本科生提供教育和就业机会，这些本科生将来布朗大学参加暑期研究项目。该项目将召集教师和学生参加布朗大学的研讨会，探讨南极洲固体地球和冰过程之间的联系。项目研究将纳入对当地公立小学和高中的推广。本研究解决了南极西部地幔过程和性质的关键问题。在岩石圈和软流圈的演化中，裂陷、地幔柱和岩石圈剥离的相对影响是什么？哪里需要地形均衡补偿，哪里需要板块弯曲或三维地幔流的牵引力等动态过程？热流和地幔粘度的界限是什么？它们代表了冰盖演化模型及其来自固体地球的反馈的重要输入。为了解决这些问题，该项目将使用尚未在南极洲应用的地震工具测量地幔和地壳性质：区域尺度的地表波地幔衰减测量；Sp体波相位成像岩石圈-软流圈边界等地幔速度梯度；表面波放大和椭圆性。在考虑地幔包体数据的同时，利用一系列实验室推导的本构定律，将对地震衰减和速度的最终模型进行联合解释，以揭示温度、总体成分、挥发性含量和部分熔体的新信息。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，将把这些过程的预测与地壳和地幔性质的新模型进行比较。为了改善南极西部热流的界限，将在经验比较和垂直温度梯度的直接模拟中使用地震衰减和速度。为了在冰川均衡调整的时间尺度上更好地测量地幔粘度，将根据推断的地幔条件估计频率相关的粘度。该项目将有助于以下人员的教育和职业发展：布朗大学博士生、布朗大学本科生和来自校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）网站参与其中，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探讨南极固体地球和冰冻圈之间联系的研讨会的基础，并将为当地公立小学和高中的推广做出贡献。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。