Modeling teleseismic P wave interference from distant oceanic sources for upper mantle reflection imaging.

At regional scale, P waves reflected on mantle discontinuities extracted by stacking seismic noise analysis are observed in cross-correlation functions (Poli et al., 2012). Under specific noise field condition, Pedersen et al. (2022), significantly improved the SNR of Pv410p and Pv660p. Initially it was assumed that the waves extracted reflected, albeit in a non perfect wave, the so-called Green's function. However, as the noise field is not perfectly distributed, the full Green's function is not retrieved, and details on these reflected wave properties (constituents in the CC, amplitudes, time bias, ...) remain unknown. We here show which major coherent phases interact to reconstruct Pv410p and Pv660p, and give a way to analyze bias between the observed cross-correlation and the Green's function, both in terms of time delays and relative amplitudes. These waves stem from long-range mantle phases that interact in the correlation function to enhance short-range reflections. We also simulated cross-correlation functions using very distant sources, ranging from a single point to realistic ocean models. The complexity of the wave field, which introduces cross terms into the correlation function, converges better when the source is extended. Our results demonstrate how to correct the simple modeling of these waves in order to obtain a detailed characterization of the observables in the noise cross-correlation. This opens up the possibility of using body-wave retrieval to obtain an accurate picture of mantle discontinuities and to constrain their compositions and temperatures using forward modeling and thermophysics.