Extracting Seismic Core Phases with Array Interferometry

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Methods that make use of seismic interferometry and ambient noise energy have proven to be extremely useful in imaging shallow Earth structure. Since application of such ambient noise techniques is not limited to where earthquakes occur, if the techniques could be applied to the deep Earth then we would drastically increase our ability to sample the deep Earth. While most studies using ambient seismic noise have failed to retrieve deep body-wave phases, new work of ours suggests that cross correlating body-wave coda emitted by large earthquakes combined with appropriate stacking of array data allows extraction of seismic phases that reflect off the Earth's core and that travel through the Earth's inner core. Currently, however, we do not fully understand why the technique works or what the limitations are. We will develop this ambient-noise/earthquake-coda core-imaging technique more fully, including understanding the basis for the method, improving the process, and applying it to interesting datasets. Promising areas of application include imaging inner core anisotropy, core mantle boundary topography, and deep mantle structure. The fundamental purpose of this work is to develop a new method of imaging the deep Earth that relies on low-amplitude but coherent waves that are part of Earth's ambient noise field. Successful application of the imaging method will provide detailed constraints on how the Earth's core has evolved, on the composition of the deep Earth, and on Earth processes in general. Our line of research will also enable us to assess the full potential of this technique to advance current imaging capabilities in the Earth sciences, but also medical imaging, and oil and gas exploration. Finally, since a crucial aspect of the method is its reliance on waves that take unusual paths, including being scattered and multiply reflected by Earth structure, understanding the method will provide new insight into the heterogeneity of Earth structure and other aspects of the Earth that cause unusual wave propagation.