A Reference Vs and Vp/Vs Model for Young Oceanic Crust From Controlled-Source OBS Data

基于受控源 OBS 数据的年轻洋地壳参考 Vs 和 Vp/Vs 模型

• 批准号: 2149630
• 负责人: Juan Pablo Canales
• 金额: $ 38.97万
• 依托单位: Woods Hole Oceanographic Institution
• 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: 2022-03-01 至 2024-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2149630&HistoricalAwards=false
• 关键词: Reference; Vs; Vp; Model; Young

Determining the properties of oceanic lithosphere and how they vary as the lithosphere ages is one of the primary methods that scientists use to infer its composition and evolution. Reference models of oceanic crust use the speed at which seismic waves travel through the Earth (i.e., seismic velocity) as their main parameter. However, current models use primarily compressional seismic waves (waves that vibrate in the same direction as they travel). This project will build a shear velocity (waves that vibrate at right angles to the direction of travel) reference model for oceanic crust and upper mantle. The model will be derived from data collected in 2012 across the Juan de Fuca tectonic plate offshore Oregon and Washington. Crustal ages in this region vary from 0 to 9 million years. This model will provide a reference framework to interpret ocean crust properties in terms of composition, modification by magmatic activity, and extent of deformation, alteration, and fracturing. The model can also be used to quantify the amount of water in oceanic crust entering deep-sea trenches that influence natural hazards such as megathrust earthquakes and arc volcanism at subduction zones. This project will support a postdoctoral investigator and a graduate student. By making use of existing seismic datasets, this project will also leverage previous investments in marine seismic acquisition.The 2012 ocean bottom seismometer (OBS) dataset includes high-quality recordings of converted waves that can be exploited to constrain shear-wave (S) velocity structure through the sediments, crust, and uppermost mantle at a plate scale from the Juan de Fuca Ridge near-axis region to the Cascadia deformation front, encompassing crustal ages from 0 to ~9 Ma. This dataset will be used to: (1) Constrain S-wave velocity structure in the shallowmost igneous crust by modeling the amplitude vs. offset of compressional (P) and P-to-S reflections from the basement and performing advanced pseudo-1D nonlinear Bayesian waveform inversion of OBS data based on a Markov Chain Monte Carlo method and time-domain elastic finite-difference simulation of P-Sv wave propagation. (2) Advanced processing of the OBS records using the theory of supervirtual refraction interferometry for improving the signal-to-noise ratio and detectability of mantle refracted S waves. (3) Conduct traveltime tomography modeling of the 2-D S-wave velocity structure of the crust and uppermost mantle along the Ridge-to-Trench transects using wide-angle crustal and mantle refracted/reflected P-to-S converted phases. (4) Investigate the azimuthal anisotropic character of the crustal and mantle S-wave velocity structure. The results will be interpreted in terms of hydrothermal alteration and porosity in-filling due to mineral precipitation within the crust and mantle as a function of age using effective medium theory. The final deliverable product of this project will be a reference model describing the shear-wave structure of oceanic crust and uppermost mantle for crustal ages of 0-9 Ma built from synthesizing the project’s results and integrating them with existing results from other seismic experiments in the region.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.

确定海洋岩石圈的性质以及它们如何随着岩石圈年龄的变化而变化是科学家用来推断其组成和演化的主要方法之一。海洋地壳的参考模型使用地震波在地球上传播的速度(即地震速度)作为其主要参数。然而，目前的模型主要使用压缩地震波(与传播方向相同的振动波)。该项目将为大洋地壳和上地幔建立一个剪切速度(与传播方向成直角振动的波)参考模型。该模型将从2012年收集的俄勒冈州和华盛顿州近海胡安德富卡构造板块的数据中得出。该地区的地壳年龄从0年到900万年不等。这个模型将提供一个参考框架，从成分、岩浆活动的修改以及变形、蚀变和破裂的程度来解释洋壳的性质。该模型还可以用来量化洋壳中进入深海海沟的水量，这些海沟会影响巨型逆冲地震和俯冲带弧形火山等自然灾害。该项目将支持一名博士后研究员和一名研究生。通过利用现有的地震数据集，该项目还将利用以前在海洋地震采集方面的投资。2012年海底地震仪(OBS)数据集包括高质量的转换波记录，可用于在从胡安德富卡海脊近轴地区到卡斯卡迪亚变形前锋的板块尺度上约束横波(S)速度结构，从0 Ma到~9 Ma。该数据集将被用于：(1)通过模拟来自基底的纵波(P)和P到S反射的幅度与炮检距的关系，并基于马尔可夫链蒙特卡罗方法和P-Sv波传播的时域弹性有限差分模拟，对OBS数据进行改进的伪一维非线性贝叶斯波形反演，从而约束最浅层火成岩地壳的S波速度结构。(2)利用超虚拟折射干涉理论对OBS记录进行进一步处理，以提高地幔折射S波信噪比和探测能力。(3)利用广角地壳、地幔折射/反射P-to-S转换震相，沿岭沟断面对地壳和上地幔的二维S波速度结构进行了旅行时层析成像模拟。(4)研究了地壳和地幔S波速度结构的方位各向异性特征。这一结果将根据有效介质理论解释为地壳和地幔内矿物沉淀引起的热液蚀变和孔隙度填充作为年龄的函数。该项目的最终交付产品将是一个参考模型，描述了0-9 Ma地壳年龄的海洋地壳和最高地幔的剪切波结构，该模型综合了该项目的结果，并将它们与该地区其他地震实验的现有结果相结合。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。