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

Rensselaer Polytechnic Institute, Troy NY

Investigators

Abstract

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.