资源环境科技发展态势分析平台

Small-scale intra-slab heterogeneity is well documented seismically in multiple subduction zones, but its nature remains elusive. Previous efforts have been mostly focusing on the scattering strength at intermediate depth (<350 km), without constraining its evolution as a function of depth. Here, we illustrate that the inter-source interferometry method, which turns deep earthquakes into virtual receivers, can resolve small-scale intra-slab heterogeneity in the mantle transition zone. The interferometric waveform observations in the Japan subduction zone require weak scattering (<1.0%) within the slab below 410 km. Combining with previous studies that suggest high heterogeneity level (∼2.5%) at intermediate depth, we conclude that the small-scale intra-slab heterogeneity weakens as slabs subduct. We suggest that the heterogeneities are caused by intra-slab hydrous minerals, and the decrease in their scattering strength with depth reveals processes associated with dehydration of subducting slabs.