Crustal Deformation across the U.S. from Harmonic Analysis of Receiver Functions

通过接收函数的谐波分析得出美国各地的地壳变形

• 批准号: 1251193
• 负责人: Vera Schulte-Pelkum
• 金额: $ 20.54万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-05-01 至 2018-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1251193&HistoricalAwards=false
• 关键词: Crustal; Deformation; across; U.S.; Harmonic

The EarthScope Transportable Array is collecting seismic data on a previously unprecedented continent-wide scale with station locations ~70 km apart. Since the thickness of the crust across the U.S. varies from ~20 - 55 km, such dense station spacing still offers mostly spot illumination of the crust under each station when teleseismic earthquake waves (with steep incidence angles under the station) are used for imaging structure. With such illumination, the crustal structure is typically assumed to be locally one-dimensional (locally horizontal interfaces) when teleseismic body waves and ambient noise and teleseismic surface waves are used. Crustal material is also typically assumed to be seismically isotropic (direction-independent wave propagation).The receiver function technique illuminates interfaces under a seismic station where an incident compressional wave partly converts to a shear wave. If an interface is not horizontal, or if a contrast in seismic anisotropy is present, the converted waves show a systematic and potentially high-amplitude signal that varies with the azimuth of arrival of the incident wave. Across the Transportable Array, roughly 20% of the radial and 40% of the transverse component total receiver function signal amplitude consists of arrivals with a systematic variation matching dipping or anisotropic interfaces, and the signal strength is well correlated to tectonic provinces. Dipping crustal interfaces as well as crustal anisotropy result from deformation of the crust. The azimuthally varying signal in receiver functions can therefore be used to map crustal deformation. Rather than attempting to fit the waveform exactly by varying interface dip and/or anisotropy, which is a highly non-unique process, this project maps the signal strength, depth, and orientation of interfaces and anisotropic layers (somewhat akin to mapping delay time and fast orientation in split SKS waves, except that the receiver function method also offers depth information). The resulting maps are compared to surface geology and models or geological histories of crustal deformation and thus offer the chance for hypothesis testing related to those models or histories. The project is based on close collaboration between a seismologist and a geologist and engages undergraduate research assistants through RESESS (Research Experiences in Solid Earth Sciences for Students, a program providing research opportunities for minority undergraduate interns by pairing them with mentors).

EarthScope 可移动阵列正在以前所未有的全大陆范围收集地震数据，站点位置相距约 70 公里。由于美国各地地壳的厚度变化范围约为 20 - 55 公里，因此当使用远震地震波（在台站下方具有陡峭的入射角）对结构进行成像时，如此密集的台站间距仍然可以提供每个台站下方地壳的大部分点照明。在这种照明下，当使用远震体波和环境噪声以及远震表面波时，地壳结构通常被假定为局部一维（局部水平界面）。地壳材料通常也被假设为地震各向同性（与方向无关的波传播）。接收器函数技术照亮了地震台下的界面，其中入射的压缩波部分转换为剪切波。如果界面不是水平的，或者存在地震各向异性的对比，则转换波会显示系统的、潜在的高振幅信号，该信号随着入射波到达的方位角而变化。在可移动阵列中，大约 20% 的径向分量和 40% 的横向分量总接收器函数信号幅度由具有与倾斜或各向异性界面匹配的系统变化的到达组成，并且信号强度与构造省份密切相关。地壳界面倾斜以及地壳各向异性是地壳变形的结果。因此，接收器函数中的方位变化信号可用于绘制地壳变形图。该项目不是试图通过改变界面倾角和/或各向异性来精确拟合波形（这是一个非常不独特的过程），而是映射界面和各向异性层的信号强度、深度和方向（有点类似于映射延迟时间和分裂 SKS 波中的快速定向，除了接收器函数方法还提供深度信息）。将所得地图与地表地质和地壳变形模型或地质历史进行比较，从而为与这些模型或历史相关的假设检验提供机会。该项目以地震学家和地质学家之间的密切合作为基础，并通过RESESS（学生固体地球科学研究经验，该计划为少数族裔本科生实习生与导师配对，提供研究机会）聘请本科生研究助理。