Global Imaging of the Lithosphere-Asthenosphere Boundary using Scattered Waves

使用散射波对岩石圈-软流圈边界进行全球成像

基本信息

批准号：
NE/G013438/2
负责人：
Catherine Rychert
金额：
$ 11.54万
依托单位：
University of Southampton
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2011
资助国家：
英国
起止时间：
2011 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FG013438%2F2
关键词：
Global Imaging Lithosphere Asthenosphere Boundary

项目摘要

The surface of our planet is composed of a number of tectonic plates, resembling an eggshell that has been cracked, but not opened. These plates are called the lithosphere. The lithosphere moves over a weak layer that is called the asthenosphere. This movement is referred to as plate tectonics. The lithosphere is constantly being destroyed, where one plate is dragged down, or subducts, beneath another, and enters the asthenosphere. It is also constantly being created, at mid-ocean ridges, where two plates are pulled apart, causing melt to rise into the void, and cool to form new crust. The earth is made of many layers, and the locations of the layers as well as the cause for the layering (e.g. changes in rock type or state) are relatively well known. However, the lithosphere-asthenosphere boundary is not globally located, nor is the mechanism that defines it well known. The interface between the lithosphere and the asthenosphere is a very important boundary in that the nature of the boundary has implications for the driving forces of plate tectonics and the origin and evolution of the continents on which we live. Plate tectonics is what drives natural disasters like earthquakes, volcanic eruptions, and tsunamis. Continent formation is puzzling since it is no longer occurring, and most continental interiors are billions of years ago. We would like to know how they formed and what enabled their formation, and stability through time, since they make up the area of the earth that is hospitable to humans. To investigate this boundary I use the energy from earthquakes, seismic waves, recorded at distant stations to image boundaries in the earth, since changes in the velocity of the earth affect the path of the waves. Seismologists have collected much seismic data over the past ~20 years at permanent seismic stations located primarily on continents. We also collect data from high density deployments of temporary arrays of seismometers. The data gives us high resolution imaging capabilities, and this allows us to constrain seismic velocity gradients in great detail. Such constraints tell us about the mechanism that defines the lithosphere-asthenosphere boundary. Experiments done on rocks help us determine the effects of various parameters like temperature, composition, and melting have on seismic waves. What they tell us is that gradual velocity gradient can be explained by the transition from a cool lithosphere, to a hotter asthenosphere. However, seismically sharp boundaries require other mechanisms to explain them. Compositional changes, i.e. mineral content and/or hydration, or a small amount of melting in the asthenosphere could be responsible for sharp velocity contrasts. Sharp boundaries mean that the lithosphere and the asthenosphere are very decoupled, and plate motions are driven by the gravitational pull of dense plates where they subduct into the asthenosphere. Gradual boundaries indicate increased coupling, and the notion that motions in the mantle beneath the lithosphere may play a larger role. We plan to look for sharp boundaries associated with the lithosphere-asthenosphere boundary, and investigate variations in the depth and character of the boundary in a variety of tectonic environments. Beneath oceans sharp boundaries are frequently imaged, and they are occasionally imaged beneath continents. It is often assumed that different mechanisms define the boundary beneath continents and oceans. However, it remains a puzzle why such a boundary would be defined in different ways in different locations. We plan to resolve this issue with global modeling of the boundary using high frequency energy that gives us information about the character of the interface. In some cases, we may also image boundaries that are interior to the lithosphere. But these are also interesting since they can tell us about the building blocks that compose the continents, with implications for their formation and evolution.

我们星球的表面由许多构造板组成，类似于被破裂但未打开的蛋壳。这些板称为岩石圈。岩石圈在一个称为软圈的弱层上移动。该运动称为板块构造。岩石圈不断被破坏，其中一块板被拖到另一个板，或者在另一个板块下方进入，并进入软圈。它也在不断地在海洋山脊上创建，在那里将两个板拉开，导致熔体升入空隙，并冷却以形成新的外壳。地球是由许多层制成的，层的位置以及分层的原因（例如，岩石类型或状态的变化）相对众所周知。但是，岩石圈 - 亚索边界不在全球位置，也不定义它的机制。岩石圈和软圈之间的界面是一个非常重要的边界，因为边界的性质对板块构造的驱动力以及我们所居住的大陆的起源和演变具有影响。板块构造是驱动自然灾害，例如地震，火山喷发和海啸。由于它不再发生，大陆的形成令人困惑，而且大多数大陆室内装饰是数十亿年前。我们想知道它们是如何形成的，是什么使他们的形成和稳定随着时间的流逝，因为它们构成了对人类热情好客的地球区域。为了研究这个边界，我使用地震，地震波的能量，记录在遥远的站点到地球上的图像边界，因为地球速度的变化会影响波的路径。在过去的大陆上，地震学家在过去的20年中收集了大量的地震数据。我们还从地震米临时阵列的高密度部署中收集数据。数据为我们提供了高分辨率的成像功能，这使我们能够详细限制地震速度梯度。这样的约束告诉我们定义岩石圈 - 心理边界的机制。对岩石进行的实验有助于我们确定温度，成分和熔化对地震波的各种参数的影响。他们告诉我们的是，可以通过从凉爽的岩石圈到更热的软圈的过渡来解释逐渐的速度梯度。但是，地震尖锐的边界需要其他机制来解释它们。组成变化，即矿物质含量和/或水合，或在进行软圈中的少量熔化可能导致尖锐的速度对比度。尖锐的边界意味着岩石圈和软圈非常脱钩，板的运动是由密集板的重力驱动的，它们将它们套管俯冲到低水圈中。逐渐的边界表明耦合增加，并且岩石圈下地幔的运动可能起更大的作用的观念。我们计划寻找与岩石圈 - 心圈边界相关的尖锐边界，并研究各种构造环境中边界深度和特征的变化。在海洋下方，经常会成像尖锐的边界，偶尔会成像在大陆下。通常假定不同的机制定义了大陆和海洋下方的边界。但是，这仍然是一个难题，为什么在不同位置将以不同方式定义这样的边界。我们计划使用高频能量为边界建模解决此问题，从而为我们提供有关界面特征的信息。在某些情况下，我们还可能成像岩石圈内部的边界。但是，这些也很有趣，因为它们可以告诉我们构成大陆的基础，这对它们的形成和进化产生了影响。