Journal of Volcanology and Seismology最新文献

We are considering in a general form several problems that have to be dealt with in prediction of great earthquakes, which pose the greatest hazard. The most important of these problems include the following: the efficiency of earthquake prediction based on the concept of scenarios, which represent the basic patterns in the evolution of the source zones generating great earthquakes; monitoring the development of such scenarios on the basis of seismological data; modeling the relationship between seismic and geodynamic processes that control the scenarios. We suggest for dealing with the last two problems to use concepts of energy and dynamic spectra of seismic activity in the geomedium, while the solution we propose has a certain peculiarity, namely, introduction of a mathematical concept of information certainty. An example in the use of proposed procedures as set forth in this paper consists in a substantiation of the hypothetical multiyear oscillating movement as the oceanic plate is subducted in the Kamchatka subduction zone at a period of about 8.57 years. It is supposed that such oscillations essentially control the most likely periods in the occurrence of regional great earthquakes.

This paper describes the chemical composition of the thermal waters discharging on the northwestern slope of the active Ebeko Volcano in the Yuriev River valley. We are using continuous multiyear observations of the evolution of chemical and isotope compositions to estimate the response of volcanic events to the state of the hydrothermal system. It is shown that phreatomagmatic eruptions of the volcano were preceded by a change in the chemical and isotope compositions of thermal waters caused by increased inflow of magmatic volatiles into the system. The springs are observed to show increased concentrations of anion-generating components (chloride, sulfate, and fluorine ions) with concurrent increases in heavier isotopes of oxygen and hydrogen (deuterium) toward “andesitic” water. Recalling that the changes were detected a few months before the eruption, we infer that such geochemical effects can serve as predictive markers when monitoring the state of the volcano.

The first detailed data are obtained on the Sr‒Nd‒Pb isotope systematics and geochemistry of Quaternary intraplate hauyne basanites and ordanshites in the Lesser Caucasus. The parental magmas of the rocks were found out to have been generated by mixing material from at least two regional sources: one relatively depleted and the other significantly enriched in incompatible elements. One of these sources of the hybrid magmas was most likely a mildly depleted regional plume–asthenospheric source of the CAUCASUS OIB type, whose isotopic-geochemical signatures were close to those of the COMMON and PREMA mantle reservoirs. The other source of the material for the rocks was relatively enriched in radiogenic Sr and Pb and depleted in radiogenic Nd and was most probably enriched subcontinental lithospheric mantle of the EM II type.

We are using data for two tsunamigenic earthquakes to develop a procedure for determining the displacement of sea bottom giving rise to tsunamis. We show that, assuming an average geometrical spreading factor for strain anomalies recorded by a laser strainmeter worldwide, we can find an approximate estimate of sea bottom displacement at a tsunamigenic site. There are more accurate spreading factors for each region where tsunamis have been generated; these can be estimated experimentally to be used for more accurate determination of sea bottom displacements.

This paper is concerned with the determination of seismicity parameters for Irkutsk Region. To tackle this problem, we have made a complete earthquake catalog for the region using a unified magnitude scale for the time span from 1962 to 2021 inclusive. The determination of seismicity parameters is an important task prior to obtaining subsequent estimates of earthquake hazard. The solution of the problem is extremely important for insurance and reinsurance businesses, since it appears feasible to employ the probabilistic approach with utmost accuracy when dealing with assessment of seismic risk, and this in turn ensures that the best management decisions are taken in order to make a stable financial system of the company concerned.

In this study we present the model of the rupture surface of the M_W = 7.0 Aykol earthquake, which occurred on the border of PRC and Kyrgyzstan on January 22, 2024, as well as the model of the rupture surface of its strongest aftershock on January 29, 2024, with magnitude M_W = 5.7 based on satellite radar interferometry data. We derived displacement fields of the Earth’s surface in the satellite line of sight for these events using Sentinel-1A imagery and resolved the inverse problem of estimating displacement fields on the rupture surfaces. The resulting rupture surface models reveal the presence of fault systems dipping towards one another. The fault plane of the main event is a thrust with left-lateral shear component dipping to the northwest. During the development of the aftershock process, a backthrust dipping to the southeast developed in the frontal region, displacing the western portion of the frontal thrust formed during the main shock. Such fault dynamics is a result of the complex structure of the fault zones in the studied region. Backthrusts in this area had been mapped during previous field works.

This paper considers two earthquakes which occurred on October 18, 2017 and October 25, 2017 in western Transbaikalia. In spite of the moderate energy level of both events, they can be treated as significant for the study area, because such earthquakes have been recorded there relatively rarely compared with the adjacent high-seismicity areas in the Baikal Rift Zone. The mechanisms of both earthquakes based on surface wave amplitude spectra showed that these events occurred under a dominating east–west near-horizontal compression and an inclined or nearly vertical NW‒SE tension, which is typical for western Transbaikalia. For both earthquakes, we also computed source parameters: scalar seismic moment M₀ = 5.0 × 10¹⁵ N m, moment magnitude M_w = 4.4, and source depth h = 7 km for the October 18, 2017 event; M₀ = 3.5 × 10¹⁵ N m, M_w = 4.3, and h = 29 km for the October 25, 2017 event. These earthquakes have caused noticeable macroseismic effects in the near-field; the maximum observed shaking intensity was IV–V (MSK-64) during the October 18, 2017 earthquake and V during the October 25, 2017 earthquake. These data were the basis for our analysis of present-day activity of faults in the study area. The results may be helpful for more accurate assessment of earthquake hazard and seismic risk in western Transbaikalia.

Geochemical and isotopic–geochemical (Sr‒Nd‒Pb) data on the Quaternary intraplate hauyne basanites and ordanshites in the Lesser Caucasus provide an insight into the most probable nature (characteristics of the composition and the depth of occurrence) of the EM II-type enriched mantle source, from which, and from the CAUCASUS OIB-type plume–asthenospheric source, the parental melts of the rocks were derived. The source of the type is demonstrated to have been modified by a subduction-related component. Data are presented on the probable timing and mechanisms of contamination of the magma-generation regions with slab material. Our data suggest that the residue in the mantle source contained garnet, amphibole, and rutile. Results obtained in the course of this study led us to conclude that the source enriched in incompatible elements was most probably subduction-modified (in the course of Mesozoic and, perhaps, also Paleogene subduction events) subcontinental lithospheric mantle of the EM II type, which likely corresponded to rutile-bearing amphibole–garnet peridotite.

This paper is concerned with the influence of the large (M_L = 6.9) 2021 Hubsugul earthquake on the seismicity of the block structure in the junction area between the Altai–Sayan mountain region and the Baikal Rift Zone. This study uses data from the networks of seismic stations operated by the Altai–Sayan and Baikal branches of the RAS Geophysical Survey, as well as from Mongolian stations. We show the evolution of the seismic process near the boundaries of the Tuva–Mongolia block and adjacent blocks in eastern Tuva. We have determined and studied the source zone of the Darkhad earthquake swarm which was formed in 2022‒2023 as several sequences of events, with the larger ones having magnitudes M_L > 5. Simultaneously with the activation of the Hubsugul earthquake source zone, we observed high seismic activity in the source zones of past large earthuuakes: 1991 Busingol, 2011‒2012 Tuva events, and 2008 Belin-Bii-Kham. The action of the Hubsugul earthquake on the seismicity in boundary blocks of the Altai–Sayan and Baikal zones was different from that of the 2003 Chuya earthquake on Altai seismicity.

This paper considers geological, mineralogical, and geochemical features of the epithermal Au‒Ag mineralization at the Televeem volcanic dome uplift (VDU) which complicates the Verkhne-Pykarvaam volcano-tectonic depression (VTD) in the Central Chukchi sector of the Okhotsk–Chukchi volcanogenic belt (OCVB). The structure of this ore occurrence is due to its localization within the eponymous VDU. The main vein zone (MVZ) of the Televeem ore occurrence, as wide as 500 m, extends for 2.5 km in the north–south direction. Along the MVZ direction, en-echelon proximal quartz–adularia veins are successively replaced with zones of thin streaks and brecciation in secondary quartzites and argillisites. The gold concentrations in these rocks vary between 1.4 and 17.3 g/t, that of gold is between 7.6 and 144.6 g/t. The ores contain abundant brecciated, framboidal lamellar, geode, and fine streaky structures. The more frequent ore minerals are pyrite, arsenopyrite, acanthite, grey ores of the freibergite–tetrahedrite series, stephanite, polybasite, low-fineness native gold (fineness varies in the range 249–532‰), and titanite. The amount of ore minerals in veins does not commonly exceed 0.5%, reaching 3% in some rare cases. Based on mineralogical evidence, this ore occurrence can be classified as belonging to low- or medium-eroded ones. The low erosion suggests a high probability of detecting buried ore bodies.