Journal of Volcanology and Seismology最新文献

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.

In the present analysis, the homogeneous, updated and complete seismic catalog of the Kohat-Potwar plateau was analyzed through dynamic time dependent statistical models. The study region earthquake interoccurrence times are assumed as a stochastic study variable and it follows one of the renewal models. A rich and updated class of statistical models was used to identify the most parsimonious one. The developed models will serve the purpose of describing, analyzing and forecasting the earthquake occurrence probabilities in the future. The model parameters were estimated through the method of maximum likelihood. Different statistical evaluation criteria were used to prioritize the estimated models according to their fitting performance to the observed data. We have found that the interoccurrence times of the study region can plausibly be described through the log-logistic model. Based on the log-logistic model, it has been found that there is a significantly high probability (>90%) of another earthquake occurrence of M_w ≥ 5.3 in the region in near future (2023‒2028). These probabilities increase with increasing time periods since the last event occurrence. The mean recurrence period of another earthquake of M_w ≥ 5.3, based on the most suitable log-logistic model, is almost three and half years with 1.80 years as standard error, i.e., 3.38 ± 1.80 years. The quantification of earthquake occurrence uncertainties in the study region provides many useful quantitative estimates that have crucial importance in seismic hazard and risk analysis studies of a region.

Iceland is a unique example where the rift zone of the Mid-Atlantic Ridge emerges at the surface, and whose morphology and tectonic structure differ considerably from typical rift zones of mid-oceanic ridges. The morphology and geodynamics of the western branch of Icelandic rifts are largely controlled by the thermal influence of the Iceland plume that has created the North Atlantic large igneous province. The western branch of Icelandic rifts is characterized by ceasing tectonic and magmatic activity. Overlapping the Eastern Rift Zone, it forms the rotating Hreppar microplate block, which results in a northward decrease of its tectono-magmatic activity. Based on a morphometric analysis of fault scarps, we identified the degree of present-day activity for individual areas of volcanic systems, and determined its variation during Late Quaternary for some areas. The inferences drawn here demonstrate distinct differences in the present-day tectonic structure and dynamics of rift zones and individual volcanic systems within them. The southernmost, transtensional Reykjanes Rift Zone shows tectono-magmatic activity decreasing to the east, which is due to a lower influence exerted by the Reykjanes Ridge that is adjacent to it to the southwest. We observed its gradual eastward diminution, which is probably due to an analogous southward movement of the most active Eastern Rift Zone and to the formation of a new transtensional zone that combines the present-day Reykjanes Rift Zone and South Iceland Seismic Zone. The Western Rift Zone is developing independently of the Reykjanes Rift Zone, having a major extension center in the area of Lake Thingvallavatn. The Holocene manifestations of tectono-magmatic activity in its northern part, as is the case in the Central Rift Zone, are very weak, being mostly due to glacio-isostatic reactivation of older structures. The identified structural inhomogeneities can also be traced in the morphological aspect of rift zones. As an example, the Western and Central Rift Zones typically contain well-developed shield volcanoes that are largely composed of hyaloclastites, while individual lava shield edifices are observed within fissure swarms. In contrast to this, the Reykjanes Rift Zone is characterized by an absence of central volcanoes expressed in topography, and chains of small volcanic vents are observed within fissure swarms.