The deep structure of the Olyutorskii earthquake rupture zone in the Koryak Upland: Geophysical evidence

This paper considers the data of magnetotelluric sounding (MTS) and gravity and magnetic surveys, as well as other geological information. We describe the methods that were used in making the observations and for interpretation of MTS data. We focus on incorporating the influence of the shift effect and the coast effect. Generalized geoelectric sections are based on mean longitudinal curves, which are less subject to distortion. Transverse curves were used for fault identification. The geoelectric sections include a sedimentary-volcanogenic layer, a high ohmic crust, and a conductive lithosphere layer. They contain faults that were detected from the divergences between oriented MTS curves and other data. The deep-seated faults in the Vyvenka basin have surface expression in the form of seismotectonic discontinuities that extend for 80 and 140 km. It was found that the hypocenters of the Olyutorskii earthquake and its aftershocks were in the crustal layer above the conductive lithosphere layer. Most aftershock hypocenters are typically situated in the area of the deep fault. We discuss a possible origin of the conductive lithosphere layer and of deep faults.