Journal of Volcanology and Seismology

Sobolev, G. A.; Zakrzhevskaya, N. A.

doi: 10.1134/S0742046320030070pmid: N/A

Records of an IRIS broadband seismic station (AAK) deployed in the Tien Shan area were studied. An STS-1 seismometer made it possible to investigate ground motion velocity in the range of a few minutes. The result was to identify asymmetric anomalies in seismic noise that differ from Earth tidal variations. These indicate the effects of local tectonic processes during some time intervals. Several large earthquakes occurred near the seismic station during the days that the anomaly was observed. The seismic noise anomalies and statistically significantly earthquakes were found to be coincident with increased amplitudes of air pressure variations.

Koloskov, A. V.; Ananyev, V. V.

doi: 10.1134/S0742046320030045pmid: N/A

This study is concerned with the mineralogical composition of volcanic ejecta in the Central Kamchatka Depression: the plateau basalts of the Ozernaya Kamchatka, Kunch, and Nikolka Stratovolcano. These data were compared with rock compositions for some volcanoes in the Klyuchevskoi Group, the plateau basalts of Bakening Volcano, and data on xenoliths of two types, viz., the “island-arc” type (Klyuchevskoi, Kharchinsky, and Sheveluch volcanoes) and the “intraplate” type (the plateau of Bakening Volcano). We have identified complementary vulcanite–xenolith pairs for which we propose a concept of dynamic evolution that envisages the ascent of melts to the ground surface accompanied by nearly synchronous change in the mineralogical composition of rocks in both pairs, while we are merely able to detect some fragments of the process. Mineralogically, the CKD riftogenic vulcanites differ from the island-arc rocks of the Klyuchevskoi Group in (1) a greater iron content of the olivines and greater concentrations of MnO and CaO in these, (2) greater titanium concentrations (over 1 wt % in the former and below 1 wt % in the latter) in clinopyroxenes, their high sodium concentration (over 0.5 wt % in the former and below 0.5 wt % in the latter), and greater (occasionally reaching 9 wt %) alumina content, and (3) the appearance of high titanium chromous spinellids, anorthoclase, and sanidine. These differences are controlled by differences in alkalinities of the melts, in the depth, composition, and the degree of melting in the mantle substrate. The compositions of the CKD rocks that we have studied, considering that the depression is a riftogenic feature, could arise in connection with a low degree of melting in the mantle sources similar to those which gave rise to intraplate subalkaline basalts in the Bakening plateau, which we treated as the standard of riftogenic volcanic occurrence.

Presnov, D. A.; Zhostkov, R. A.; Likhodeev, D. V.; Beloborodov, D. E.; Dudarov, Z. I.; Dolov, S. M.

doi: 10.1134/S0742046320030057pmid: N/A

This paper presents the results of areal seismic studies in the deep structure of the Dzhau Tepe mud volcano, which is the largest of its kind on the Kerch Peninsula. It is the first time that data has been obtained concerning nearly vertical fluid-conducting structures beneath the volcano that supply material onto the ground during more active periods. A new approach is proposed for interpretation of measured relative amplitudes of microseismic noise based on numerical simulation of plane-stratified media. The results derived in this study are compared with previous geological and geophysical data on the area.

Shablinskii, A. P.; Vergasova, L. P.; Filatov, S. K.; Moskaleva, S. V.; Nazarova, M. A.; Bubnova, R. S.

doi: 10.1134/S0742046320030069pmid: N/A

This paper presents the results of mineralogical and crystallographic studies in the first Russian finding of a mineral belonging to the fluoride class, viz., knasibfite, which was found in fumarolic deposits discharged during the Great Tolbachik Fissure Eruption. We investigated its crystal structure to corroborate the fact that knasibfite is orthorhombic, sp. gr. Imm2; a = 17.181 (2), b = 5.537 (4), c = 9.205 (7) Å, V = 875 (1) Å3. The structural features that can be seen in this mineral classify it as belonging to a special group of compounds that has inherited its structure from a high temperature modification or from the medium where it crystallized.

Gobarenko, V. S.; Yegorova, T. P.

doi: 10.1134/S0742046320030033pmid: N/A

This new seismic tomography study for the crust of southern Crimea and the northeastern Black Sea based on low-magnitude (M ≤ 3) earthquakes indicates significant heterogeneity of the crust at depths of 15–35 km. In the present paper we discuss the velocity distribution for P- and S-waves and give geological and tectonic interpretations in the context of collisional interaction between the Black Sea microplate and the Scythian plate. The joint use of data on both types of waves (P- and S-waves) increases the reliability of the interpretation and allows us to estimate the crustal composition of Mountainous Crimea (MC) and subcrustal mantle of the northeastern Black Sea. We have detected high velocity regions in the MC crust (Vp = 6.5‒6.8 km/s, Vs = 3.7‒3.9 km/s, Vp/Vs = 1.75‒1.9), which have complex configurations and can be deep sources of mid-Mesozoic intrusions known in the MC (Ayu-Dag and Castel). The high-velocity area is separated from eastern Crimea by a linear nearly north–south low-velocity zone located between the cities of Sudak and Feodosiya. The latter is interpreted as a weakened crustal zone associated with the Korsak–Feodosiya fault. The high-velocity region beneath the Black Sea (south of Kerch Peninsula) at depths of 25–40 km most likely belongs to the subcrustal mantle (Vp/Vs = 1.80–1.85) that underlies a thin suboceanic crust of the East Black Basin. The resulting crustal model for southern Crimea and adjacent part of the Black Sea is consistent with the parameters of other geophysical fields.

Glukhov, A. N.; Sedov, B. M.

doi: 10.1134/S0742046320030021pmid: N/A

Satellite imagery was used to identify active neotectonic faults. The areas of greater fault density coincide with concentration zones of earthquake epicenters, including the largest of them (K ≥ 10). The earthquakes are confined to intersections of deep NE and NW striking faults. The Kulu–Tenka region can be considered as the area of interaction between the zones of dynamic influence of faults that separate the Eurasian, North American, and Pacific plates.