Full waveform ambient noise inversion

Korbinian Sager, Christian Boehm, Laura Ermert, Lion Krischer, & Andreas Fichtner

Published August 14, 2018, SCEC Contribution #8548, 2018 SCEC Annual Meeting Poster #106

We develop and apply a novel full waveform ambient noise inversion that jointly constrains 3D Earth structure and heterogeneous noise sources at the global scale. Modern tomographic techniques aim to exploit details in waveforms for the benefit of improved resolution. Their application is so far mostly limited to transient point sources, e.g. active sources or earthquakes. Despite the widely-used assumption that the inter-station correlation of noise recordings is equal to a scaled version of the Green function between both receivers, a transfer to ambient noise tomography is not readily feasible. The required assumptions of Green function retrieval, e.g. wavefield diffusivity and equipartitioning, or equivalently the isotropic distribution of both mono- and dipolar uncorrelated noise sources, are typically not satisfied on Earth. Heterogeneous and non-stationary noise source distributions inevitably leave an imprint on correlation waveforms. To exploit their full waveform information regarding noise generation and Earth structure, we develop a method – referred to as full waveform ambient noise inversion – that is valid for arbitrary noise source distributions in both space and frequency, and which accounts for the full seismic wave propagation physics in 3D heterogeneous and attenuating media.

The forward problem of modeling correlation functions and the computation of sensitivity kernels for noise sources and Earth structure are implemented based on the spectral-element solver Salvus. Many studies, which were previously impossible or complicated to conduct, are now rendered feasible. For a first use case, we investigate the emergence of signals in correlation functions in general and in particular of body waves. In contrast to surface waves, body waves likely emerge from very localized sources and their interpretation as pure body waves is prone to misinterpretation due to significant cross-terms. In addition, we present a first application of full waveform ambient noise inversion with real data, a global data set focusing on the Earth's hum period band. We jointly invert for the distribution of noise sources and Earth structure.

Sager, K., Boehm, C., Ermert, L., Krischer, L., & Fichtner, A. (2018, 08). Full waveform ambient noise inversion. Poster Presentation at 2018 SCEC Annual Meeting.

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