Coda-correlation Tomography: Theory and Examples

Abstract:

Global coda-correlograms – stacks of many thousands of cross-correlation functions of late earthquake-coda – are characterized by a multiplicity of prominent features, which, if understood thoroughly, could supply valuable information on the structure of Earth’s interior. The features in global coda-correlograms exist due to many cross-terms of reverberating body-waves, a principle fundamentally different from the reconstruction of surface waves in the ambient-noise correlograms. To further refine our knowledge and be able to utilize this information, we derive a theoretical framework for coda-correlation tomography.

We first demonstrate that coda-correlation features are dominated by cross-terms of coherent seismic waves in the late-coda time window, 3 hours after the earthquake origin. Our analysis demonstrates that the cross-terms sample different parts of Earth, although they contribute to the same coda-correlation feature. We then quantify the relationship between the cross-terms and the Earth’s structure. We derive the sensitivity kernels that establish a theoretical framework for coda-correlation tomography.

We will present selected examples of coda-correlation tomography applied to different parts of the Earth’s interior, including the core and the mantle. These applications aim at an improved illumination of the deep Earth that is not well constrained by conventional seismological investigations.