Small-scale instraslab heterogeneity constrained from inter-source interferometry

Quasi-laminated small-scale scatterers within subducted slabs at intermediate depth (<350 km) have been required to explain the enhanced ground motion along the trench (e.g. Furumura and Kennett, 2005). However, the origin of these laminar scatters is poorly understood. To address this puzzle, we apply inter-source interferometry to probe the depth dependence of the intraslab heterogeneity by turning deep earthquakes into "virtual receivers". By cross-correlating the coda waves from deep earthquake pairs, the Green's function from one earthquake to the other can be effectively reconstructed. Without interferences from shallow heterogeneities, this method has been applied to detect the metastable olivine wedge (MOW) beneath the Japan Sea. In this study, based on the previously obtained MOW model, we further explore the slab heterogeneity structure below 410 km depth. We find that the velocity perturbation of these intraslab scatters in the mantle transition zone is constrained to be less than 1.5%, which is substantially lower than that at intermediate depth (~2.5%). Therefore, the subduction of slab into the mantle transition zone must have reduced the anomaly by phase changes or dehydration processes.

Reference:

Furumura, T., and B. L. N. Kennett (2005), Subduction zone guided waves and the heterogeneity structure of the subducted plate: Intensity anomalies in northern Japan, J. Geophys. Res.,110, B10302, doi:10.1029/2004JB003486.