CMG: Adaptation of Microlocal and Time-Reversal Techniques to Tomographic Analysis of Locally Recorded Earthquake Seismograms

通常伴随着当地记录的中小型地震的分散振动，被称为地震尾波，可能包含关于它们所经过的构造的大量信息，但在大多数情况下，这些信号被认为过于复杂，无法以确定性的方式进行解释。记录技术、处理能力和成像理论的最新进展现在提出了开采这种资源并使用它来生成地下图像的方法。这项研究的主要目标是开发、实施和测试两种成像技术的应用--微局部和时间反转技术--以当地记录的地震的尾波作为观测来表征地球内的弹性波散射体。我们将把这些技术应用于加利福尼亚州中部圣安德烈亚斯断层附近收集的地震数据，以成像断裂带的结构。该项目的结果将对圣安德烈亚斯断层的特殊应用和地下成像的一般规律产生影响。我们研究的地区经常发生大地震(6级)，也是SAFOD钻探项目的所在地，该项目旨在穿透和监测断层的孕震部分。我们希望，我们的结果与钻探工作的结果相结合，将提供有关震源物理的新信息，并导致对地震发生的时间和地点的新见解。在更广泛的范围内，由于地球上几乎所有地方都会发生小地震，而且我们的结果直接推广到人工震源，我们开发的分析工具将对需要地下图像进行研究的科学家和工程师有用。例子包括对描述水库特征感兴趣的环境科学家和对监测基础设施感兴趣的土木工程师。

The scattered vibrations that typically accompany local recordings of small- to medium-sized earthquakes, referred to as the earthquake coda, potentially contain a wealth of information about the structures through which they pass, but for the most part these signals have been considered too complex to interpret in a deterministic fashion. Recent advances in recording technology, processing capabilities, and imaging theory now suggest ways to mine this resource and use it to generate images of the subsurface. The principal objective of this research is to develop, implement, and test applications of two imaging techniques -- the microlocal and time reversal techniques -- to characterize elastic wave scatterers within the Earth using as observations the coda of locally recorded earthquakes. We will apply these techniques to seismic data collected near the San Andreas fault in central California to image the structure of the fault zone.The results of this project will have implications both in the particular application to the San Andreas fault and for the general discipline of subsurface imaging. The area we study frequently experiences large (magnitude 6) earthquakes and is the site of the SAFOD drilling project that aims to penetrate and monitor the seismogenic part of the fault. We expect that our results, when combined with those from the drilling effort, will provide new information about the physics of the earthquake source and lead to new insights into why earthquakes occur when and where they do. On a broader scale, because small earthquakes occur nearly everywhere on Earth, and because of the straightforward generalization of our results to artificial sources, the analysis tools we develop will be useful to scientists and engineers who require subsurface images for their research. Examples include environmental scientists interested in characterizing reservoirs and civil engineers interested in monitoring infrastructure.