Body Waves Retrieved From Noise Cross-Correlation Reveal Lower Mantle Scatterers Beneath the Northwest Pacific Subduction Zone

Abstract

Seismological studies have revealed heterogeneities at scales of 10–1,000 km in the lower mantle. For the first time, we demonstrate here that seismic interferometry of ambient noise can be used to detect faint scattered waves. We locate scattering structures at depths of ~900–1,000 km from P-to-P scattered wave signals in stacks of vertical cross-correlograms from dense seismic arrays in northeast China. Independently, we show that this scattering structure produces S-to-P converted signals in the recordings of a deep earthquake. We constrain the thickness (H), the contrasts of the shear wave speed (δVs), and density (δρ) of the anomaly using 1-D synthetics. Our modeling of both the reflected and converted signals indicates that H = 10–20 km, δVs = −7.2%, and δρ = 0.6%, which are similar to values reported previously and consistent with the interpretation that the scattering structure is a fragment of the basaltic oceanic crust associated with the subducted Izanagi plate.