CAREER: Illuminating the Tectonic History of North America with Seismic Models of Shear Attenuation and Velocity

标题：职业生涯：用剪切衰减和速度的地震模型阐明北美的构造史北美大陆的地质条件千差万别，从西部的火山和山脉，到支撑美国中部的内陆平原，以及滚滚进入大西洋的广阔的阿巴拉契亚山脉。这一地形反映了大陆几十亿年来经历的多次大陆碰撞、分裂和改造。S地表的构造板块运动与S地幔的岩石运动(地幔对流)密不可分。理解地球内部和表面之间的联系？S对于解决大陆是如何形成的、它们如何随着时间演变以及它们是如何被摧毁等基本问题至关重要。这项研究将使用地震产生的地震波来成像北美下面的地壳和地幔的性质，特别强调在三维成像地震波所经历的能量损失(衰减)。虽然人们普遍认为地震衰减有可能成为关于地球-S内部的一个有价值的信息来源，但很难将地震衰减与其他波传播现象分开，这在历史上限制了研究人员对地震衰减的使用。综合研究和教育活动将利用NSF EarthScope US阵列地震仪记录的数据，该地震仪记录了可能是现有的最好的数据集，以应对这些挑战。该项目将使用新的数据分析和地震波场模拟，调查北美地下剪切衰减的三维变化。这项研究还将建立上地幔剪切速度的三维模型，并通过与衰减模型以及衰减和波速的实验室测量的联合解释，对北美上地幔的温度、成分、部分熔融和水的变化施加限制。衰减模型将根据在整个美国毗邻的US阵列站的瑞雷波幅度和体波衰减的测量得出，而速度模型将根据瑞雷波的旅行时间和本地场地放大观测得出。根据弹性结构和滞弹性衰减分离聚焦对瑞雷波幅度的竞争影响是成像小尺度衰减变化的主要障碍；美国阵列公司已经实现的高分辨率弹性模型的频谱元素模拟将用于计算聚焦效果，精度大大提高。教育活动的对象是高中生和本科生。教育地震仪将安装在国际扶轮普罗维登斯地区的两所高中。这些地震仪和美国阵列台站记录的数据将被用来让高中生学习地震科学、波的基本性质和北美的构造史。将开发和更广泛地传播利用这些数据的针对下一代科学标准(NGSS)的教学模块。在本科阶段，暑期实习生将在三个暑假期间在布朗大学开展研究项目，并将开发一门新的环境地球物理实地课程。

Title: CAREER: Illuminating the Tectonic History of North America with Seismic Models of Shear Attenuation and VelocityThe North American continent contains vastly diverse geology, from the volcanoes and mountains in the west to the interior plains that anchor the central United States and the broad Appalachian hills that roll into the Atlantic Ocean. This topography reflects the many episodes of continental collision, breakup, and modification that the land mass has experienced over billions of years. The movements of the tectonic plates at Earth?s surface are inextricably linked to the movement of rocks in Earth?s mantle (mantle convection). Understanding the connection between the Earth?s interior and surface is essential to addressing fundamental questions about how continents are created, how they evolve over time, and how they are destroyed. This study will use seismic waves generated by earthquakes to image the properties of the crust and mantle beneath North America, with particular emphasis on imaging in three dimensions the energy loss (attenuation) experienced by seismic waves. While it is generally acknowledged that seismic attenuation has the potential to be a valuable source of information about the Earth?s interior, it is difficult to isolate attenuation from other wave-propagation phenomena, which has historically limited its use by researchers. Integrated research and education activities will utilize data recorded by the NSF EarthScope USArray seismometers, which have recorded what is likely the best data set in existence to confront these challenges.This project will investigate, using new data analysis and seismic-wavefield simulations, the three-dimensional variations in shear attenuation beneath North America. This study will also develop a 3-D model of shear velocity in the upper mantle and, through joint interpretation with the attenuation model and laboratory measurements of attenuation and wave speed, place constraints on the variations in temperature, composition, partial melt, and water in the North American upper mantle. The attenuation model will be derived from measurements of Rayleigh wave amplitude and body-wave attenuation at USArray stations throughout the contiguous United States, and the velocity model will be derived from Rayleigh wave travel-time and local site-amplification observations. Separating the competing effects of focusing by elastic structure and anelastic decay on the Rayleigh wave amplitudes is the primary obstacle to imaging small-scale attenuation variations; spectral-element simulations with high-resolution elastic models for the U.S. that have been made possible by USArray will be used to compute focusing effects with greatly improved accuracy. The educational activities are targeted at high-school and undergraduate students. Educational seismometers will be installed at two Providence, RI area high schools. Data recorded by these seismometers and USArray stations will be used to engage the high-school students in earthquake science, fundamental properties of waves, and the tectonic history of North America. Teaching modules utilizing these data that address the Next Generation Science Standards (NGSS) will be developed and disseminated more widely. At the undergraduate level summer interns will carry out research projects at Brown during three summers, and a new field course in Environmental Geophysics will be developed.