Abstract—This paper is concerned with ground deformation and seismicity prior to the Tolbachik Fissure Eruption, which began in Kamchatka on November 27, 2012. Seismic and GPS data were analyzed to reveal synchronous precursory anomalies in crustal deformation and seismicity that lasted approximately 4 months (August to November 2012). The seismic anomaly was a statistically significant increase of seismicity with low energy (mostly KS = 4–6) beneath the Ploskii Tolbachik Volcano edifice at depths of less than 5 km. The rates of seismicity and seismic energy release were exceeded by factors of approximately 40 compared with the
2000–2011 mean values during the 2 to 3 weeks immediately before the eruption. The strain anomalies were observed as movements in the middle of the Klyuchevskoy volcanic group: a radial (relative to the eruption) compression and an extension in the tangential direction. The strain had reached ~ 10^–7 by the beginning of the eruption. The durations of the seismic and strain anomalies were comparable in value (~ 4 months before the eruption), thus providing evidence of a common origin. We can classify them as belonging to the same time scale of precursors (the intermediate�term in the accepted terminology).

Получены новые палеомагнитные определения по лавовым потокам и вулканическим пеплам Северной группы вулканов Камчатки, удовлетворяющие современным методическим и аппаратурным требованиям к проведению палеомагнитных исследований. В интервале последних 4000 лет исследовано 12 стратиграфических уровней, датированных тефрохронологическим методом. Полученные направления геомагнитного поля восполняют недостаток данных по вековым вариациям для северо-востока Азии и могут быть использованы при разработке глобальных моделей геомагнитного поля. Кроме того, показана перспективность использования вариаций геомагнитного поля для региональной корреляции вулканических событий.

The article presents data on horizontal and vertical surface deformations obtained during geodetic measurements in 1976-2011 around the North Vent of the 1975-1976 Greate Fissure Tolbachik Eruption. Instrumental measurements of the relative vertical deformations show lowerings to 233 cm associated with the surface deflection due to formation of cinder cones and thick deposits of fresh lavas. The decrease of baselines suggests horizontal compressive strains caused by stress relief, arisen during the eruption, and volume reduction of cooling-down near-surface basalt dykes.