Journal of Volcanology and Seismology最新文献

Eruptions of Hunga Tonga Hunga Ha’apai render a unique opportunity to explore the mechanism, environmental and climatic effects. Although the size of blast occurred on 15 January was large, the ashes emitted were small, and the global surface air temperature is likely to decrease by about 0.03–0.13°C in the next few years. The dominant reason for this disproportionateness is that vast majority of SO₂ and particles were removed before escaping out of the shallow water and soaring up into the upper atmosphere (∼30 km). The explosive eruptions had devastated this Pacific Island nation, and all things in the Tongatapu Island were covered by up to 2 cm thick ash layer. One puzzling phenomenon is that a sequence of low-frequency waves rippled globally in the atmosphere probably due to the continuous oscillations of gas bubbles shells at the magma-air interface. Furthermore, the atmospheric waves had regenerated the sea waves far-away from the volcano and exerted certain influence on ocean circulation and marine ecology, and thus the short-term explosive eruption may play far-reaching impacts. Given the series problems Tonga had faced after the blast, one realistic suggestion is that adequate preparations should be made in the emergency security and post-disaster reconstruction.

This paper discusses the results of solving the problem of tsunami hazard assessment for the northeastern coast of Kamchatka around the village of Korf which is situated on a sand spit in the northwestern part of the eponymous bay. This assessment was based on the “worst case” procedure. The seismicity and historical data on tsunami occurrences in the western Bering Sea were examined to identify three tsunami-generating zones: the near zone (the Bering Sea part), the regional zone (the Aleutian part), and the far (Chilean) zone as posing the greatest tsunami hazard for this stretch of the northeastern coast of Kamchatka. An analysis of seismicity and tectonics of the source zones yielded sets of modeled tsunami-generating earthquakes that are typical of each. For these sets we performed numerical modeling of tsunami generation and propagation which has identified the most dangerous model sources. The sea level rises due to these sources for the Korf area were 1.3 m for earthquakes from the near (Bering Sea) zone, 2.4 m for the regional (Aleutian) zone, and 2.5 m for the far (Chilean) zone. The next step consisted in more accurate calculations for such earthquakes in sequences of nested calculation grids, yielding characteristics of tsunami effects on the shore. The main results of this study consist in identification of tsunami-generating zones that are the most dangerous for the Korf Spit, selection of the model earthquakes for these, and estimation of extreme tsunami wave heights posing hazard for this coast segment.

This paper is devoted to the 130th anniversary of the discovery of the Omori law. This first law in earthquake physics was formulated in 1894, and has become widely known since that time as the Omori law. It was found that the frequency of aftershocks following an earthquake decays approximately obeying the hyperbolic law on average. This was an epoch-making discovery. It has governed the line of research in the study of aftershocks for many decades ahead. Attention is mainly focused in the present paper on one of the modern lines of research in the phenomenological theory of aftershocks. A new method has been developed within the framework of that theory for aftershock data processing and analysis. The theory is based on the differential equation governing the evolution of an earthquake source after the main rupture has been formed in rocks in that zone. The differential approach, unlike Omori’s algebraic approach, allows one to get a new insight into the experimental study, processing, and analysis of aftershock data. Proceeding as outlined above, we have discovered the existence of the so-called Omori epoch, which terminates by bifurcation. The basic simple nonlinear evolution equation whose solution is identical with the Omori law suggests natural extensions of the phenomenological theory. In particular, one such extension which has the form of the Kolmogorov–Petrovsky–Piskunov equation enables a hypothetical relationship to be developed connecting the propagation of aftershock activity to Umov’s energy flux at the source.

Cross-spectral analysis was applied to the results of a nearly one-year LIDAR monitoring of aerosol emanation from the Earth’s crust in the tunnel of the Baksan Neutrino Observatory at the Institute of Nuclear Research, Russian Academy of Sciences (BNO). It was found that ∼40% of LIDAR signal energy is controlled by the variation of meteorological factors, namely, air pressure (the effect of “barometric pumping“) and humidity. The important fact is that the signal modulation involves components in the crustal deformation due to lunisolar tidal waves М2 and О1. We provide a statistical justification for the potential of LIDAR as a new tool in the monitoring of local seismic activity based on crustal aerosol variations.

This paper presents instrumental parameters and macroseismic data for the Shipunsky earthquake of August 17, 2024, ML = 7.0, M_W = 7.0. We discuss its tectonic setting and the aftershock process based on the first month of observation after the main event. The mechanisms and parameters for the Shipunsky earthquake and its largest aftershocks presented here were derived by an original procedure to calculate seismic moment tensors developed at the KB GS RAS. The directions of rupture and the orientations of rupture planes for these events enable us to relate their generation to the subduction of the Pacific plate under the Okhotsk plate on which Kamchatka lies. The Shipunsky earthquake has not caused loss of human lives and damage to buildings. Its maximum macroseismic effect was observed in the Shipunsky Peninsula, which was shaking of intensity 6 on the SIS-17 scale (GOST P 57546–2017); the intensity of shaking in the town of Petropavlovsk-Kamchatsky was 5–6. No tsunami alert has been issued, and no tsunami has been recorded.

This paper provides new data on the age (U–Pb, LA-SF-ICP-MS: 86 ± 1 Ma) of quartz monzodiorites of the Viktorisky complex in the Konginsky igneous zone of the Omolonsky cratonic terrane. The Labaznoe ore occurrence, which contains streaky-stockwork sulfide–quartz and vein polymetal mineralization, is localized within an intrusive dome uplift in whose central part a monzodiorite stock of the Viktorinsky complex is exposed. Petrographic and geochemical characteristics and mineral thermobarometry of the ore-bearing quartz monzodiorites are provided. Ore mineralogy is gien along with an estimate of the isotopic age (K–Ar: 82 ± 4 Ma) for the crystallization of sericite from a circumvein contact with the monzodiorite intrusion. Geological interrelationships and isotopic geochronologic data are used to find a paragenetic relation between the porphyry molybdenum mineralization and the phase of Late Cretaceous magmatism, viz, emplacement of Viktorinsky granitoid bodies. The phases have been reconstructed involving the formation of paragenetic mineral associations in the sequence magnetite–quartz, molybdenite–quartz, and sulfide–quartz; the hypogene phase terminates in a polymetallic phase. The materials of isotope dating of the ores and of ore-bearing granitoids in the area of study provide evidence of a Late Cretaceous (Coniacian‒Campanian) age of the porphyry igneous ore system in the Konginsky igneous zone.

The present paper reports first data on the Holocene explosive activity of Zavaritsky Volcano—a major caldera center on Simushir Island, Central Kurils. We have managed, for the first time ever, to reconstruct the chronology of explosive eruptions in this volcanic center for the last 10 thousand years, as well as to estimate the parameters of its larger eruptions. Overall, more than 40 tephra layers have been identified in pyroclastic soil sections, enabling us to estimate the frequency of eruptions, one event per every 250 years. The age model based on radiocarbon dates that we determined for proximal deposits and on published data for the tephra of Zavaritsky Volcano and for the CKr key tephra layer have enabled us to find the ages of most eruptions. It was found that the volcanic glasses of the Holocene pyroclastics have compositions corresponding to low-K basaltic andesites and rhyolites; the very low concentration of K₂O is a reliable indicator to distinguish the Zavaritsky tephra, not only from that of adjacent medium-K volcanoes, but also from the tephra of the other low-K volcanoes in the Kuril–Kamchatka island arc. The Holocene activity of Zavaritsky Volcano began with two major eruptions whose conservative magnitude estimates (М) were 6.4 and 5.6. These events occurred about 9.5 ka and 9.2 ka ago. The tephra of the earlier eruption (ZV-1) propagated northeast, and was found as far as the northwestern North America. The tephra of the second large eruption (ZV-3) has traveled north, and was found in sediments of the Sea of Okhotsk. The ZV-1 pyroclastics is characterized by volcanic glass of rhyolitic composition with the highest concentration of SiO₂ (72.5–74.0 wt %). The glasses in the ZV-3 eruption products varied between dacites and rhyodacites (65.0–71.9 wt % SiO₂). The products of later eruptions were cinders with glasses of the dacite–andesite and basaltic andesite compositions. Dacite glasses appeared again only in the tephra of the latest large explosive eruption which occurred a short time before the mid-19th century. Our study has revealed a catastrophic character of the Early Holocene explosive eruptions of Zavaritsky Volcano and its practically constant activity throughout the Holocene. The fact that the tephra of the last large eruption of this volcano (ZV-40) contained high silica glasses tells us that a large eruption is likely to occur in the near future.

4-D seismic tomography study was conducted in the northwestern region of Iran using travel time tomography during 1996 to 2016. The study area is situated within the active tectonic and seismic zones of the collision between the Eurasian and Arabian plates. This region has experienced multiple significant and destructive earthquakes in the past. Furthermore, it includes Lake Urmia, which has undergone a substantial decrease in water level by about 8 meters during the study period. To minimize the artifacts caused by uneven distribution of seismic rays, similar data sets including about 700 earthquakes in each period were selected for five periods. Subsequent experiments utilizing synthetic models demonstrated that the selected subsets of data for different time periods have the potential to identify anomalies in different periods. 3-D tomography was performed for each selected data sets, and the results were compared across different time periods. The results, focused on two depths of 8 and 23 kilometers and receiving significant attention, exhibit certain similarities in the observed anomalies across different time periods. These anomalies correspond to the tectonic structures of the region. Some differences are also observed among the various time periods. The trends of most anomalies and the differences in velocity models across different time periods are consistent with the general trends of the active faults in the area. The majority of the differences in velocity models for different time periods are observed at a depth of 8 km, along northwest-southeast-trending faults.

The epithermal Au–Ag mineralization at the Pechalnoe deposit is of considerable interest, since it was formed in carbonaceous terrigenous rock sequences making the basement of a volcanic dome structure at a distance of about 200 km from the boundary of the Okhotsk–Chukchi marginal continental volcanic belt. The geological structure of the Pechalnoe deposit consists of two levels, quartz–adularia and quartz Au–Ag veins are localized in keratinized terrigenous rocks of the lower level, while the quartz rhyolites and comendites of the Pechalninskaya rock sequence in the upper level harbor potential industrially valuable REE mineralization. The productive veins make three zones striking nearly east–west; the veins in these zones are 200–300 m long, occasionally reaching 640, 840 m; the mean thickness is 0.1–3 m, rarely reaching 6.2 m; the mean concentrations are Ag 266 g/t, Au 4.4 g/t. The following mineralogical features of the ores have been identified: low sulfides (1‒2%); the productive minerals are native Ag, low fineness Au, polybasite, and high-selenium acanthite. In addition, the ores have abundant enough arseniferous pyrite, arsenopyrite, pyrrhotine, ferruginous sphalerite, chalcopyrite, and marcasite. The geochemical features of the ores are in good agreement with their mineral composition. The ores are enriched in a wide range of trace elements (arranged in decreasing concentration): Ag, Au, As, Sb, Sе, W, Tl, Li, Be, Bi, Cs, and Mo; light lanthanoids prevail over heavy ones; very low Eu/Sm ratios (( ll 1)), little inclined near-chondrite distributions (without distinct europium maxima or minima); the relationship between Ce/Ce* and Eu/Eu* indicates oxidizing conditions during the mineralization; the REE spectra are dominated by light “hydrophile” lanthanoids of the “cerium” group; ΣREE varies in a wide range. The mineralogical and geochemical data obtained enable us to classify the Pechalninskaya mineralization as belonging to the selenium subtype of the low sulfide class of epithermal deposits. According to geological and mineralogic-geochemical evidence, the deposit can be classified as poorly eroded, which suggests future identification of new ore bodies not at the ground surface.

This study presents an analysis of event clustering in volcanic seismicity, especially in volcanic swarms. We have analyzed the volcanic swarms occurring during the eruptions of Bárðarbunga (2014) and Fagradalsfjall (2021) volcanoes in Iceland, attempting to use the nearest neighbor method for this goal. The method enables identification of clusters with different scales of generalized distance; as an example, the method generally identifies two clusters of events in tectonic seismicity and is widely used in aftershock identification. We have detected considerable differences in the distributions of generalized distance to the nearest neighbor for volcanic seismicity compared with tectonic seismicity. To be more specific, we have discovered two types of unimodal distribution, with the one mostly occurring before eruptions and the other during eruptions. The former type is probably due to coalescence of two near modes in the distribution, and reflects an internal inhomogeneity in seismicity during such periods. However, the unimodal nature of the distributions makes it difficult to identify events viewed as interrelated (clustered) or independent (background events). It can be surmised based on the results obtained that, before an eruption, the percentage of background seismicity fluctuates around 70%, while being between 90 and 100% during the eruption. This can be considered as providing evidence of different sources of seismicity during different phases of an eruption.