Interferometric Imaging of Subduction Zones

地震和火山活动是直接影响美国和世界各地大量人口的现象。这些机制的主要驱动力可以在俯冲带内的地表深处找到-两个构造板块相互移动的区域，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，该技术允许将地震等源数字化为能够在没有物理设备的位置记录信号的虚拟地震检波器。预计所提出的算法将最终产生更高质量和更高保真度的图像。这些图像将为俯冲带内部的重要物理过程及其在触发地震、震颤和火山活动中的作用提供额外的线索。在为成像目的选择采集几何结构时，最好将物理源和接收器放置在尽可能靠近感兴趣区域的位置。这样做可以提高信号能量，改善该区域的照明，增加有效接收器孔径，并大大减少长距离波传播引起的信号误差。 虽然许多地震自然地起源于俯冲地壳或地幔内部，但将接收器放置在几十公里深的俯冲带内在技术上是不可能的。地震干涉测量提供了一种重新标定（数字移动）位于地面的接收器的方法，就好像它们位于震源位置一样。然后，当地地震可以作为物理源，或者在需要时作为虚拟接收器。我们的新技术结合了经典的地震干涉测量法和源-接收器波场干涉测量法，使用了地震事件以及大型本地地震产生的数据，并将它们转换为虚拟数据，如果我们在俯冲板内实际上有物理接收器，我们就会观察到这些数据。这种重新基准面化过程的最大好处是建立了一个虚拟的局部地震勘测，可以用来精确地生成我们最感兴趣的区域的图像。 我们已经开发了声学的情况下的方法，本项目中，我们将工作扩展到弹性的情况下，并调查必要的源和接收器的分布的方法，以产生高质量的数据，从其中可以形成一个详细的图像俯冲板。

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.