Interferometric Imaging of Subduction Zones

俯冲带的干涉成像

• 批准号: 1141812
• 负责人: Alison Malcolm
• 金额: $ 12万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-01-15 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1141812&HistoricalAwards=false
• 关键词: Interferometric; Imaging; Subduction; Zones

Earthquakes and volcanism are phenomena that directly affect a large number of people in the US and throughout the world. A major driving force for these mechanisms can be found deep down under the surface inside subduction zones -- areas where two tectonic plates move towards each other, one sliding underneath the other. Seismic imaging is a method of estimating rock properties, which in turn reveal physical processes that take place in the subsurface. The quality of seismic images depend on many factors, the most important of which are the location of seismic sources (earthquakes) and recording devices (geophones) as well as signal distortions caused by the complicated nature of the Earth's interior. This project aims at developing a novel seismic signal processing algorithm that removes many of the problems associated with traditional imaging methods. This algorithm is based on seismic interferometry, a technique that allows to numerically turn sources such as earthquakes into virtual geophones capable of recording a signal at a location where no physical device can be placed. It is expected that the proposed algorithm will ultimately result in higher-quality and higher-fidelity images. Those images will provide additional clues about the important physical processes inside the subduction zones and their role in triggering earthquakes, tremor, and volcanic activity.When choosing the acquisition geometry for imaging purposes, it is ideal to place physical sources and receivers as close to the area of interest as possible. Doing so boosts the signal energy, improves the illumination of the area, increases the effective receiver aperture and greatly reduces the errors in the signal introduced by wave propagation over long distances. While many earthquakes naturally originate inside the subducted crust or mantle, placing receiversinside the subduction zone at the depth of tens of kilometers is technologically impossible. Seismic interferometry provides a method of redatuming (numerically moving) receivers located at the surface to be as if they were located at the source locations. Local earthquakes can then act as physical sources or, when desired, as virtual receivers. Our new technique, which combines classical seismic interferometry and source-receiver wavefield interferometry, uses teleseismic events as well as data produced by large local earthquakes and converts them into virtual data that we would have observed had we actually had physical receivers inside the subducting slab. The great benefit of this redatuming procedure is the construction of a virtual local seismic survey that can be used to produce an image of precisely the area that we are most interested in. We have already developed the method for the acoustic case; with this project we will extend the work to the elastic case and investigate the necessary source and receiver distribution for the method to produce high-quality data from which a detailed image of the subducting slab can be formed.

地震和火山活动是直接影响美国和世界各地大量人的现象。这些机制的主要驱动力可以在地表深处的俯冲带中找到--两个构造板块相互移动，一个在另一个下面滑动。地震成像是一种估计岩石性质的方法，这反过来又揭示了地下发生的物理过程。地震图像的质量取决于许多因素，其中最重要的是震源(地震)和记录设备(地震检波器)的位置以及地球内部复杂性质造成的信号失真。该项目旨在开发一种新的地震信号处理算法，消除与传统成像方法相关的许多问题。该算法基于地震干涉测量法，这项技术允许将地震等震源以数字方式转换为虚拟地震检波器，能够在不能放置物理设备的位置记录信号。预计所提出的算法最终将产生更高质量和更高保真度的图像。这些图像将提供更多关于俯冲带内重要物理过程的线索，以及它们在触发地震、震动和火山活动中的作用。在选择用于成像目的的采集几何时，理想的做法是将物理震源和接收器放置在尽可能靠近感兴趣区域的位置。这样做提高了信号能量，改善了区域照度，增加了有效接收器孔径，并大大减少了由于波在长距离传播而引入的信号误差。虽然许多地震自然起源于俯冲的地壳或地幔内部，但在数十公里深的俯冲带内安装接收器在技术上是不可能的。地震干涉测量提供了一种将位于地表的接收器重新基准化(以数字方式移动)的方法，使其如同位于震源位置一样。然后，当地的地震可以作为物理震源，或者在需要的时候，作为虚拟接收器。我们的新技术结合了经典的地震干涉测量和震源-接收器波场干涉测量，使用了远震事件和当地大地震产生的数据，并将它们转换为虚拟数据，如果我们在俯冲板块内实际有物理接收器的话，我们就会观察到这些数据。这种重新基准面程序的最大好处是建立了一个虚拟的局部地震测量，可以用来精确地生成我们最感兴趣的区域的图像。我们已经开发了用于声学情况的方法；通过这个项目，我们将工作扩展到弹性情况，并调查该方法所需的震源和接收器分布，以产生高质量的数据，从中可以形成俯冲板块的详细图像。