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

标题：职业：用剪切衰减和速度的地震模型照亮北美的构造历史北美大陆包含了大量不同的地质，从西部的火山和山脉到锚定美国中部的内陆平原和广阔的阿巴拉契亚山脉，这些山脉延伸到大西洋。这种地形反映了大陆在数十亿年里经历的许多次大陆碰撞、分裂和修改。地球构造板块的运动？地球的表面与地球上岩石的运动有着千丝万缕的联系。S地幔（地幔对流）了解地球之间的联系吗？大陆的内部和表面对于解决一些基本问题至关重要，这些问题包括大陆是如何形成的，它们是如何随时间演变的，以及它们是如何被破坏的。这项研究将利用地震产生的地震波对北美地壳和地幔的特性进行成像，特别强调对地震波经历的能量损失（衰减）进行三维成像。虽然人们普遍认为地震衰减有可能成为有关地球的宝贵信息来源？在内部，很难将衰减与其他波传播现象隔离开来，这在历史上限制了研究人员的使用。综合研究和教育活动将利用美国国家科学基金会EarthScope USArray地震仪记录的数据，这些地震仪记录的数据可能是目前应对这些挑战的最佳数据集。该项目将利用新的数据分析和地震波场模拟，研究北美地下剪切衰减的三维变化。本研究还将开发上地幔剪切速度的三维模型，并通过与衰减模型的联合解释以及衰减和波速的实验室测量，对北美上地幔的温度、成分、部分熔体和水的变化进行限制。衰减模型将根据美国各地USArray台站对瑞利波振幅和体波衰减的测量得出，而速度模型将根据瑞利波传播时间和当地站点放大观测得出。分离弹性结构聚焦和非弹性衰减对瑞利波振幅的竞争效应是成像小尺度衰减变化的主要障碍；由USArray实现的美国高分辨率弹性模型的光谱元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大学生。教育地震仪将安装在两所普罗维登斯，罗德岛地区的高中。这些地震仪和美国地震阵台站记录的数据将用于让高中生参与地震科学、波的基本性质和北美的构造历史。将开发和更广泛地传播利用这些数据处理下一代科学标准的教学模块。在本科阶段，暑期实习生将在布朗大学进行为期三个夏季的研究项目，并将开设一门新的环境地球物理学野外课程。

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.