Seismic anisotropy in the lowermost mantle near the Perm Anomaly

Abstract

The lower mantle is dominated by two large structures with anomalously low shear wave velocities, known as Large Low-Shear Velocity Provinces (LLSVPs). Several studies have documented evidence for strong seismic anisotropy at the base of the mantle near the edges of the African LLSVP. Recent work has identified a smaller structure with similar low-shear wave velocities beneath Eurasia, dubbed the Perm Anomaly. Here we probe lowermost mantle anisotropy near the Perm Anomaly using the differential splitting of SKS and SKKS phases measured at stations in Europe. We find evidence for lowermost mantle anisotropy in the vicinity of the Perm Anomaly, with geographic trends hinting at lateral variations in anisotropy across the boundaries of the Perm Anomaly as well as across a previously unsampled portion of the African LLSVP border. Our observations suggest that deformation is concentrated at the boundaries of both the Perm Anomaly and the African LLSVP.