编号 1 (2024)

The paper presents the data on the April 11, 2023 Sheveluch Volcano eruption. We conducted post-eruption impact assessment. The directed blast resulted in the collapse of the lava dome which had been forming for more than 42 years. The data obtained just before the eruption evidence that the total volume of the lava dome comprised about 0.53 km3. The volcanic explosion resulted in the formation of the field of pyroclastic deposits ~70 km2 in size and 0.49 km3 in volume. The directed blast was accompanied by the 25–30 km long pyroclastic flows and the ashfall more than 200 km away from the volcano. The weight of the ash deposits samples was ranging from 1.2 to 43.9 kg/m2, depending on the distance from the volcano. The area of ash deposits (ash samples of more than 50 g/m2 in weight) covered the area of 17000 m2 and comprised the volume of 0.09 km3. Taking into account the total volume of erupted products (0.6 km3), the April 11, 2023 Sheveluch Volcano eruption can be referred to the largest catastrophic eruption of this century.

We study characteristics of short-period shear wave attenuation field in the lithosphere to pick out areas of possible preparation for large and great shallow earthquakes. We have processed more than 360 seismograms of events with source depths of 0–33 km recorded by station PET from two areas limited by coordinates of 45.0˚–50.5˚ N and 54.0˚–56.5˚ N, respectively (for brevity, we will call the areas as the southern and the northern ones). Besides, for the purposes of comparison we have analyzed seismograms by station KGB that recorded earthquakes from the area located between 52˚ и 54˚ N. We used the method based on analysis of Sn and Pn maximum amplitude ratio. We find that attenuation in the lithosphere of the northern area is generally much higher than in the southern one. At the same time attenuation in both areas is weaker than in the region of north-eastern Japan. Relatively lower attenuation corresponds to rupture zones of the great earthquakes of 1952 (Mw = 9.0) and 1963 (Mw = 8.6) occurred in the southern area more than 50 years ago. Higher attenuation is observed in the rupture zones of the recent events dated 1997 (Mw = 7.8), 2006 (Mw = 8.3) and 2018 (Mw = 7.3). The obtained data are in agreement with earlier conclusions stating that typical large subduction type earthquakes occur in the areas characterized by higher fluid content in the uppermost mantle; and large and great earthquakes are followed by deep fluids ascent during a few decades, which leads to attenuation decrease in the uppermost mantle. We also pick out the high attenuation zones where no large and great earthquakes (Mw ≥7.8) have occurred for quite a long time. We suggest that active processes of preparation for large earthquakes can be observed in these zones (first of all in the area of the Avacha Bay and to the east of it).

A generalization of the available original data and literature data on the geological and geophysical knowledge of the underwater volcano Esmeralda, located in the Mariana Island Arc, has been carried out. As a result of studying the rocks dredged during the 4th and 5th cruises of the R/V Vulkanolog at the present level, new data were obtained on the silicate and rare-element composition of the rock samples that make up this underwater volcano. It has been established that the studied volcanic edifice is composed of five types of rocks: basalts, basaltic andesites, dacites, gabbro, and basanites. For the first time, samples of dacite and basanite have been discovered, indicating that the petrochemical diversity of the underwater volcano Esmeralda is wider than previously thought. All dredged rocks are characterized by a slightly increased content of incoherent elements LILE and HFSE. The studies carried out made it possible to attribute the main part of the dredged rocks to the association of island-arc ferruginous tholeiites (IAB, IAT) and only the composition of a single sample of alkaline basalt (basanite) falls into the field of alkaline basalts of oceanic islands (OIB, OIA). The increased content of iron in plagioclase phenocrysts confirms that the rocks belong to the high-iron tholeiite association.

The paper examines poorly-studied negative bay-like anomalies in the near-earth atmospheric electric field in seismically active regions at fair weather suitable for atmospheric electric observations. Observation data analysis revealed characteristic features of anomalies formation that allow us to conclude that the anomalies are associated with the deformation of near-surface rocks at tectonoseismic process. On the basis of the concept of atmospheric electricity, the source of anomalies in the electric field is a local negative space charge of small ions in the near-earth air emerged at a negative vertical gradient of electrical conductivity. It was revealed that the charge and produced negative anomalies in the electric field have deformation and emanation processes in their origin. We propose a scheme of anomalies formation and consider the role of radon and thoron in their emergence. It was found that thoron plays a more important role in some cases.