Seismic Imaging of Alaska Using Spectral-Element and Adjoint Methods

使用谱元和伴随方法对阿拉斯加进行地震成像

• 批准号: 1215959
• 负责人: Carl Tape
• 金额: $ 28.59万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1215959&HistoricalAwards=false
• 关键词: Seismic; Imaging; Alaska; Using; Spectral

This project will apply spectral-element and adjoint methods to develop a three-dimensional seismic reference model for the crust and uppermost mantle of Alaska. Finite-frequency surface waves and body waves will be extracted from full seismic waveforms in order to provide the greatest resolution for seismic imaging. Major sedimentary basins will be incorporated within the initial three-dimensional models by using existing information such as gravity data and industry seismic data. A new catalog of seismic moment tensors will be constructed by inverting measurements of body waves and surface waves for earthquake depth and radiation pattern.Active tectonic settings exhibit deformation in the form of earthquakes, geodetic strain rate, erosion, and sedimentation. On longer time scales, these processes create a highly heterogeneous crustal composition. For example, faults may offset two distinct rock types, or a basin may open and accumulate kilometer-thick layers of sediment. On shorter time scales, these settings experience abundant earthquakes in response to stresses within the crust. By using these abundant earthquakes, seismic imaging with accurate numerical methods can reveal the extreme complexity within active tectonic settings. Spectral-element methods have been used to model wave propagation in complex geological settings, such as those with strong topographic variations and sedimentary basins. The accuracy of these wave propagation methods can be embedded in an adjoint inverse problem to improve subsurface images of Earth's crust. The primary product will be a three-dimensional reference model for Alaska. This model will describe the spatial variations in compressional wave speed, shear wave speed, and density in Alaska. The quality of the model will be highest in the crust, and it will provide opportunities for larger-scale tomographic studies of the entire subduction and collisional setting. The reference model will be useful as a framework for the upcoming GeoPRISMS focus in Alaska as well as the anticipated EarthScope Transportable Array.

该项目将应用谱元和伴随方法来开发阿拉斯加地壳和上地幔的三维地震参考模型。将从完整的地震波形中提取有限频率的表面波和体波，以便为地震成像提供最大的分辨率。主要沉积盆地将利用重力数据和工业地震数据等现有信息纳入初始三维模型中。将通过反演体波和面波的地震深度和辐射模式测量来构建新的地震矩张量目录。活跃的构造环境以地震、大地应变率、侵蚀和沉积的形式表现出变形。在较长的时间尺度上，这些过程产生了高度异质的地壳成分。例如，断层可能会抵消两种不同的岩石类型，或者盆地可能会打开并积累千米厚的沉积物层。在较短的时间尺度上，这些环境会因地壳内的应力而经历丰富的地震。通过利用这些丰富的地震，采用精确数值方法的地震成像可以揭示活动构造环境中的极端复杂性。谱元方法已用于模拟复杂地质环境中的波传播，例如具有强烈地形变化和沉积盆地的环境。这些波传播方法的准确性可以嵌入到伴随反问题中，以改善地壳的地下图像。主要产品将是阿拉斯加的三维参考模型。该模型将描述阿拉斯加压缩波速、剪切波速和密度的空间变化。该模型的质量将是地壳中最高的，并且将为整个俯冲和碰撞环境的更大规模层析成像研究提供机会。该参考模型将作为即将在阿拉斯加进行的 GeoPRISMS 重点以及预期的 EarthScope 可移动阵列的框架。