The Avacha–Koryaksky Volcanic Group: Geophysical Inhomogeneity of the Lithosphere and Processes at Depth (Kamchatka)

This paper reports the results of seismic, electromagnetic, and gravity surveys, as well as seismicity data in the lithosphere at depth for the active volcanoes in the Avacha–Koryaksky group which is part of the East Kamchatka volcanic belt. We have developed an integrated geophysical model for the crust and lithospheric mantle in the area of study. The resulting distribution of crustal geophysical inhomogeneities, in particular, beneath Avacha Volcano, was used to study the main features of intracrustal fluid saturation and of pathways as channels for deeper fluids to rise to the upper crust. The integrated model assumes that the stresses that arise at boundaries of zones with different conditions of defluidization constitute one of the factors to produce seismicity beneath the active volcanoes. We also incorporate data from regional seismic tomography to deal with a general scheme for deep processes in the lithosphere and the system that supplies magma to the volcanoes. It is assumed that active volcanoes, in particular, Avacha, are connected to the asthenospheric layer of the lithosphere mantle at a depth of about 70–120 km, whence fluids/melts are coming into the magma chamber in the lower crust with subsequent formation of a peripheral chamber in the upper crust beneath the volcanic cone due to the heat supplied by the lower crustal source.