Extracting Seismic Core Phases with Array Interferometry

利用地震干涉测量和环境噪声能量的方法已被证明是非常有用的成像浅层地球结构。由于这种环境噪声技术的应用并不局限于地震发生的地方，如果这种技术可以应用于地球深处，那么我们将大大提高我们对地球深处采样的能力。虽然大多数使用环境地震噪声的研究都未能检索到深部体波相位，但我们的新工作表明，大地震发出的交叉相关体波尾波与阵列数据的适当堆叠相结合，可以提取出从地核反射并穿过地球内核的地震相位。然而，目前我们还不能完全理解为什么这项技术有效，或者它的局限性是什么。我们将更全面地发展这种环境噪声/地震尾波核成像技术，包括了解该方法的基础，改进过程，并将其应用于有趣的数据集。有前景的应用领域包括成像内核各向异性、核幔边界地形和深部地幔结构。这项工作的基本目的是开发一种新的地球深部成像方法，这种方法依赖于作为地球环境噪声场一部分的低振幅但相干波。成像方法的成功应用将为地核如何演化、地球深部的组成以及地球的一般过程提供详细的限制条件。我们的研究路线也将使我们能够评估这项技术的全部潜力，以推进当前地球科学成像能力，以及医学成像和石油和天然气勘探。最后，由于该方法的一个关键方面是它依赖于采取不寻常路径的波，包括被地球结构散射和乘法反射，因此了解该方法将为了解地球结构的非均质性以及导致不寻常波传播的地球其他方面提供新的见解。

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.