Body-wave seismic interferometry

Recent success of body wave retrieval from noise or coda correlations that creates new 3-D paths other than laterally propagating surface waves has advanced our ability of probing and monitoring deep Earth. Growing applications have been made for imaging Moho and transition zone discontinuities, D” reflector, inner core structure, and potentially monitoring volcanic system at depth, showing great promise to complement earthquake-based data. Applying earthquake coda interferometry techniques to 1846 USArray stations deployed across North America from January 2004 through September 2013, we show that the spatial analysis of the differential travel time residuals between two core phases, PKIKP2 and PKIIKP2, reveals significant short-wavelength variation and implies the existence of strong structural variability in the deep Earth. Especially, a linear N-S trending anomaly across the middle of the U.S. may reflect an asymmetric quasi-hemispherical structure deep within the inner core with boundaries of 99°W and 88°E (Huang et al., 2015). Moreover, in collaboration with NASA Jet Propulsion Laboratory, we also prove the applicability of seismic interferometry to determining the discontinuity structure of Europa (Panning et al., 2017).

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