№ 5 (2025)

This paper provides an overview of the available relationships for calculating magnitudes from earthquake signal durations, as well as a refinement of the magnitude relationship for bottom seismic records. The original formula was obtained as a result of seismological monitoring in the Aegean Sea. The correction was performed using the data from a number of experiments with ocean bottom seismographs and using data from on-land seismic stations. The experiments were conducted in the waters of the internal and marginal seas of the Russian Federation: the Caspian, Baltic, Black, Laptev Sea, and in the Pacific Ocean. To model signals of microearthquake with a magnitude less than 1, records of an air gun obtained using an ocean bottom seismograph in the Black Sea were used. The corrected magnitude ratio is recommended to be used for processing in processing earthquake records obtained by ocean bottom seismographs with a number of limitations, which are mainly associated with the parameters of local seismic noise at the location of the ocean bottom seismographs.

A consolidated seismogeological section of the Earth's crust along the Northern Sikhote-Alin–Sakhalin with a length of 350 km and a depth of 40 km on the area of 51.7°– 52.4° N, 138.5°– 143.3° E was compiled. The seismic information on the eastern end of the Basalt Geotraverse and the results of previous deep seismic surveys by deep seismic sounding (DSS) and earthquake converted-wave method (ECWM) were used. The section shows not only the relief and position of the basement and Mohorovicic discontinuity, but also the boundaries in the volcanogenic-sedimentary complex and in the consolidated part of the crust. Comparison of the depth-velocity structure with the distribution of local earthquake hypocenters has shown that the seismically active region of Northern Sakhalin and the adjacent part of the Tatar Strait is characterized by crustal seismicity confined to the large regional faults and their feathering disturbances.

Quaternary lavas from the Gorely volcano (Kamchatka) contain microinclusions of native metals, silver, copper and tin alloys, silver and copper sulfides and chlorides occassionally with minor tin, uranium and carbonaceous matter, as well as tungsten carbides, cassiterite and barite. These assemblages of microinclusions are similar to the typomorphic mineral associations in the epithermal deposits from the Russian Far East, as well as in some uranium- and silver-rich iron oxide-copper-gold (IOCG) deposits in Australia. Lavas from the Gorely volcano contain elevated Ag, W and, to a lesser extent, Cu, Mo, Cd, Bi contents. Some Gorely samples exhibit elevated Sn and Sb concentrations in comparison with other Kamchatka volcanoes. We conclude that the ore metal mobility is caused by presence of sulfur and chlorine in hydrothermal fluids that accompanied crustal evolution of Gorely magmas along with their emplacement at the surface and, possibly, post-eruptive transformation in active fumarolic fields. Assemblages of microminerals observed in the Gorely lavas may record early stages of formation of epithermal, porphyry and IOCG magmatic-hydrothermal ore systems in the process of volcanic activity in modern subduction zones.