Evidence for a Lithospheric Fragment Beneath Klyuchevskoy Volcano From Seismic Data of Local and Teleseismic Earthquakes

Volcanoes of the Klyuchevskoy Group (KG) form one of the most active volcanic clusters on the planet, yet its position relative to the subducting Pacific Plate is unusual in regard to the conventional features of flux-induced arc volcanism. With the subducting Pacific plate positioned at 170km depth, the KG is seemingly outside the maximum fluid flux release zone of 100km, as observed across global subduction-zone environments. Past geophysical studies indicate a planar low velocity seismic anomaly 110km below the KG, and it has been noted that the KG lavas exhibit anomalous geochemical signatures: pyroxenite source melts alongside peridotite melts. This interpretation is based on receiver-function (RF) estimates from seismic data recorded by the Partnership in International Research and Education (PIRE) seismic network. We present additional results of teleseismic and locally sourced receiver functions, combined with teleseismic shear-wave splitting, focused on a temporary-array dataset surrounding the Klyuchevskoy Group.

We present our findings in the form of depth-migrated receiver-function images incorporating a three-dimensional model of the subduction zone, along with shear-wave birefringence measurements. Our results increase the resolution of the previously identified upper-mantle anomaly by using higher-frequencies in the RFs, with geographic extensions both vertically and laterally. We complement our observations with a forward-modeling effort of both the PIRE network of stations and a temporary array aimed at assessing the geological nature of the anomaly. We show that a remnant paleoslab remains a likely geodynamic scenario that explains both the observed geophysical anomaly and its impact on volcanic activity of the KG.