After a short period of quiescence, in February 2019, Karymsky volcano (Kamchatka Peninsula, Russia) became active. During the month, a large number of moderate explosions were recorded, some of which were preceded with some periodicity by long-period earthquakes with a high degree of similarity of waveforms. The duration of the multiplet events that preceded the explosions ranged from 4 to 70 minutes. The period between earthquakes decreased as the multiplets developed. The amplitude of earthquake records either increased or remained at the same level. The multiplets with higher amplitude of earthquake records preceded the strongest eruptions. The decreasing period between earthquakes is most likely related to the acceleration of magma ascent and an increase in gas pressure in the volcanic channel. If this is true, the absence of long-period earthquakes after the eruption marks a complete release of gas pressure in the volcanic edifice.

This is the first paper presenting the case study for the active Koryaksky and Klyuchevskoy Volcanoes that shows the temporal relationship between the volcanic earthquakes (the volcanic EQ) and strong tectonic earthquakes (the tectonic EQ) in the world with Мw ≥ 6.3 at the final stage (less than a week) of their preparation (regardless the epicenters and depths of the tectonic EQ). The article shows that in 2009 the volcanic EQ at Koryaksky Volcano occurred 3 days prior to the tectonic EQ in the world and their number was in general anomalously high. 12 of 18 volcanic EQ alerted about the strong world events 3 days prior to the tectonic EQ. In 2008-2009 such effects typical for Klyuchevskoy Volcano as well, were used along with the other forecasting anomalies (including the deformation monitoring) for real-time forecast of the strong tectonic EQ in the world with the delay time equal to 6 days.