Data of seismological, gravimetric and electromagnetic study are presented. Main peculiarities of deep-seated structure of the earth's crust and upper mantle to the depth of ~90 km have been revealed. Margins of the lithosphere blocks on ground and water area of the Avacha bay have been established. A complex geologic-geophysical model beneath Avachinsky volcano has been developed. It involves crustal magmatic chamber at depth 15 to 25 km, intrusion overlying it, peripheric chamber at depth ~0 to 2 km, and zone saturated with liquid fluids in Avachinsky graben. Major geodynamic processes, which have been operating in the earth's crust at present, are considered. An important role is given to the crustal permeable zone containing fluids. Recommendations are made for the deep well-drilling in the area of Avachinsky volcano with the aim of searching for geothermal deposits.

Results are presented from gravity, seismic and electromagnetic studies. Main features of the deep structure of the area have been identified. A multidisciplinary geologic-geophysical model has been developed for the crust beneath Avacha Volcano. The model involves a crustal magma chamber at a depth of about 15-25 km, an intrusion that overlies it, and a peripheral chamber under the volcanic cone at 0-2 km depth, as well as a fluid-saturated zone in the Avacha Graben. We discuss possible geodynamic processes that are going on in the crust at present. Importance is attached to the fluid-containing crustal permeable zone. Recommendations are provided for drilling a deep well in the Avacha Graben area to search for a geothermal field.

Рассмотрены методика и результаты магнитотеллурического зондирования в модификациях АМТЗ и МТЗ. Аудиомагнитотеллурическое зондирование (АМТЗ) было проведено впервые в районе современного извержения Толбачинского вулкана. Результаты анализа магнитотеллурических параметров свидетельствуют, что геоэлектрическую среду, в связи с региональным разломом, можно аппроксимировать в виде двумерно-неоднородной модели. В качестве основных для интерпретации приняты продольная и поперечная кривые зондирований. Совместный анализ этих кривых и псевдоразрезов фаз импеданса свидетельствуют о геоэлектрической неоднородности среды в районе прорыва магматических расплавов им. С.И. Набоко. По данным бимодальной инверсии кривых АМТЗ получен геоэлектрический разрез, содержащий проводящую неоднородность, связываемую с разломом, по которому флюиды поступают к дневной поверхности. Наряду с АМТЗ для изучения глубинной электропроводности использованы МТЗ в расширенном диапазоне, по которым выделяется коровая проводящая аномалия на глубинах 15–35 км. По данным АМТЗ, МТЗ и другой геолого-геофизической информации составлена концептуальная модель района, характеризующая возможную природу аномальных зон. Даны приближенные оценки пористости пород в разломной зоне, по которой магматические расплавы поступали в вышележащие толщи в районе прорыва им. С.И. Набоко.

The article presents the methods and results of the magnetotelluric sounding within the Avacha-Koryaksky group of volcanoes. Geoelectrical section was studied within the period range from 0.0001 to 1000 seconds and above. The authors performed a numerical two-dimensional modeling. Initially, we used test models for possible distortions of curves. The analysis of the magnetotelluric parametres allowed us to characterize the geoelectrical inhomogenuities. Curves along the strike and across the strike were used as main curves. Since longitudinal curves are less prone to coast effect, they were used with transverse curves in order to create a geoelectrical model based on a 2D magnetotelluric field numerical modeling. The created geolectrical model has a conductive bed in the upper part of the section that is connected with an igneous-sedimentary cover. The deep part of the model includes near-vertical conductive zones, which denote a zone with deep faults. The paper describes possible nature of the revealed anomalies and provides rough estimation of rock porosity in the conductive zones.

Long-term investigations in the Ushkovsky Volcano caldera were completed in June 1998 using deep drilling of the crater glacier filling the Gorshkov summit cone. A 212-m ice core containing 354 bands of volcanic ash was obtained. The possibility of using an analysis of these data in paleovolcanic reconstructions of the northern volcano group is discussed.