Journal of Volcanology and Seismology最新文献

Shallow fault reactivation has been identified, likely related to the 5.69 M_w East Lombok earthquake on March 17, 2019. Using relocation hypocenters and a focal mechanism analysis, the structure can be analyzed. The relocation results showed a more geologically meaningful hypocenter distribution than before relocating, which enabled a structural analysis. In this case, the mainshock clearly showed a dipping slip (a strike angle of ∼97°, a dipping angle of ∼66°, and a rake of ∼102°) extending ∼25 km from the northeast to the southwest. After cross-correlation, the largest relocated aftershock (M_w 5.1) either occurred on the same ruptured plane as the mainshock or was not caused by a different earthquake source. From the analysis of geological data, the mainshock was related to an inland fault close to the Sembalun caldera. Additionally, the high stress of the 2018 Lombok earthquake may have triggered the 2019 East Lombok earthquake according to Coulomb stress changes. This study provides valuable information about the addition of the active fault zones on Lombok Island, improving our understanding of this unique seismic activity in an unusual place. Moreover, the Sembalun region is one of the most popular tourist destinations on Lombok Island. Consequently, this study is crucial for developing future seismic risk mitigation strategies.

This study is the first examination of the geological structural and mineralogical-geochemical features of the Perevalnoe silver-polymetallic deposit, Northeast Russia. The deposit lies in the northeastern flank of the Dukat ore field in the middle of the Balygychan–Sugoi riftogenic volcanic depression which was formed synchronously with the structures of the Okhotsk–Chukchi volcanogenic belt (OChVB). The deposit lies along the periphery of a volcanic dome rise and is localized in a large subvolcanic dike consisting of Late Cretaceous porphyritic rhyolites (nevadites) at a depth of 140–160 m beneath the ground surface. The richest mineralization is controlled by geniculate bends in the dike. The bulk of silver in the ores is mostly related to Ag-tetrahedrite and freibergite. As well, a substantial amount of silver is due to pyrargyrite, native silver, acanthite, and the sulfurous analogue of geffroyite ((Ag, Cu, Fe)₉(Se, S)₈). A small fraction of silver is related to rare (for these ores) minerals, namely, proustite, argentopyrite, and minerals of the isomorphous series lenaite (AgFeS₂)—chalcopyrite. The chief mineralogical peculiarity of these ores consists in a wide occurrence of coarse-flake muscovite and rutile, the presence of rhodonite, anatase, zirconium, and leucoxene. The carbonates are dominated by siderite and rhodochrosite. The Perevalnoe deposit was found to involve a two-phase mineralization, namely, telescoped superposition of high-temperature greisens (those of the later phase) upon silver-polymetallic ores (those of the earlier phase) with distinct signs of thermal metamorphism of the latter and the associated natural enrichment in Ag. Greisenization and the arrival of high-temperature brine seem to be related to the emplacement of the later phase of an unexposed intrusive massif. The results of mineralogical studies enable us to classify the Ag-polymetallic Perevalnoe deposit, similarly to the other mineral deposits in the Omsukchan metallogenic zone, as the intermediate sulfidation epithermal class of deposits.

The water balance is considered for the summit crater lakes on the Vernadsky Range, Paramushir Island. The input was based on precipitation at the crater heights. The necessary condition for the existence of permanent cold crater lakes with a precipitation of ∼4660 mm per hydrologic year is a drainage area exceeding 60 thousand m². The evolution of the lakes lying in the craters of the active Ebeko Volcano is discussed. An estimate is provided for volcanic input (inflow of water and/or vapor of volcanic origin) into thermal lakes during the preceding time periods and during the present-day condition of the volcano. The Middle Crater and the Korbut Crater are suitable for the formation of hot lakes. The formation of a lake in the Korbut Crater is impossible until the eruption in the crater has come to an end. A volcanic input of 8–13 kg/s will be sufficient for an equilibrium existence of a lake with temperature 35°С and water area 25 thousand m², assuming a crater diameter of 250 ± 50 m during the post-eruption period. The supply of volcanic vapor into Lake Goryachee in the Middle Crater has been recorded since 2017, but the lake remains cold. The volcanic input must be 5 ± 2 kg/s in order to achieve a balance equilibrium for a lake with temperature 35°С and water area 25 thousand m².

We report for the first time to our knowledge an asymmetry in the signals of the laser strainmeter at the Baksan Neutrino Observatory (BNO), Elbrus area during the first and second earthquakes in Turkey on February 6, 2023, which had nearly identical magnitudes. A correlation has been detected between the signals of the laser strainmeter and the temperature inside the bedrock foundation in the BNO dead-end tunnel, as well as the signal of aerosol lidar during the second magnitude 7.7 earthquake occurring at 10:24 UTC. The radius of the stress zone around the epicenters was estimated as ∼2000 km, which exceeds the distance to the BNO tunnels (~900 km) and thus admits of the variations of stress and strain to be seen in the signals of the laser strainmeter, the thermometer, and the lidar.

Isotope geochronology applied to several occurrences of young volcanic activity on the northern slope of the Greater Caucasus in the Chegem River basin, Kabardino-Balkaria, Russia, which were classified by different researchers as belonging to either the Jurassic Period or to the Late Cenozoic, aided toward determining their age and place in the regional geochronological scale of the Neogene–Quaternary magmatism occurring in the Elbrus neovolcanic area. We have established stratigraphic interrelationships between the geological objects studied here and the products of catastrophic explosive volcanism, which resulted in the formation of the large Chegem Caldera in the study region at the end of the Neogene. We determined more accurately whether the volcanic vents that were active in the Late Pliocene could be classified as belonging to the pre-caldera, syn-caldera, or post-caldera stages of magmatism. The results of K–Ar dating obtained here show that the endogenous activity in the region of study was of areal character during the pre-caldera stage (about 3.1 Ma). During that period volcanic occurrences were taking place at many small volcanic vents that are at present completely demolished and are marked by dikes and stocks of rhyolites, less frequently of trachyandesites. At the end of the Pliocene, during the period 2.9–2.8 Ma, catastrophic explosive eruptions occurred giving rise to the Chegem Caldera filled with a thick sequence of rhyolite–dacite ignimbrites. According to the data acquired by us, a series of acid extrusions and dikes composed of vitrophyres were emplaced along its western, southern, and eastern periphery simultaneously with the caldera formation. The post-caldera stage (about 2.8 Ma) saw activity exhibited by Kum-Tyube and Kyugenkaya stratovolcanoes in the western part of the caldera which discharged lavas of dacitic composition, and later on also of andesitic composition. It was found that no volcanic activity has been occurring during Quaternary time throughout almost all of the basin of the upper reaches of the Chegem River. One exception is furnished by the environs of the Aktoprak Pass in the northwestern part of the area of study where local manifestations of moderately-alkaline magmatism were recorded to occur in the Early Pleistocene (about 1 Ma). Several geological objects (Bashil Dam and others) which were previously dated by some researchers to the period between the end of the Pleistocene and the Holocene are in fact either Pliocene syn-caldera extrusions or were formed by exogenous processes unrelated to volcanic activity.

This paper describes the results of the 2024 visual and instrumental observations of eruptions at Grot Geyser in Geyser Valley, Kamchatka. It was found that the eruption behavior of Grot Geyser has significantly changed: while previously being an irregularly erupting geyser, Grot had become a relatively regularly erupting geyser whose interval between eruptions were 10.4 h during the winter low-water period, an intermission during the most intensive flood, and a subsequent resumption of geyser activity at intervals of 24 h. The volume discharged by a Grot eruption is estimated as ≈70 m³ using the chloride tracer method.

In this study we develop a synthetic earthquake catalog for the Eastern Sector of the Russian Arctic Zone (RAZ). The catalog reproduces and simulates the key properties of the catalog that includes all earthquakes that have actually occurred in the region. Considered at the regional level, the Gutenberg–Richter law for earthquakes of different magnitudes holds both for the catalog as a whole and for the mainshock catalog with aftershocks eliminated. Local values of the parameters involved are reproduced. The synthetic catalog includes aftershocks, and local relationships between the numbers of aftershocks and the total number of earthquakes based on the catalog of actual events are retained. Our model for the spatial distribution of large (М ≥ 5.5) earthquakes in the region uses the results of the FCAZ recognition applied to identification of possible locations of future large earthquakes. Preliminary calculations have been performed to find the normative intensity in order to compare three versions of the synthetic catalog (the full model, one without aftershocks, and one that does not include the FCAZ results and aftershocks).

With the purpose of unifying the earthquake catalog for the Kuril–Okhotsk region we derived a two-segment linear relation between the magnitude based on the surface wave MLH as reported by the Sakhalin Branch of the GS RAS and the moment magnitude M_W as reported by the GCMT and NIED. Comparison to analogous relations based on other catalogs shows that for large (MLH = 6.5–8.1) earthquakes there is a small (∼0.1) excess of regional magnitude MLH over the M_S in other catalogs. MLH exceeds the values of M_S by 0.2–0.4 in the interval MLH = 4.0–6.5. We have obtained relations connecting MLH and M_L as reported by the Kamchatka Branch of the GS RAS in the area of the Middle-Northern Kuril Islands, and MLH and M_j of the JMA for the southern part of the region. Conversion using the relation MLH(M_W) has repeated with good accuracy the relations derived directly. The best result is achieved when the differences between the determinations of M_W as reported by different agencies have been taken into account.

This paper discusses the potential of a new algorithm for earthquake prediction based on a set of precursory anomalies that have been previously identified reliably by construction and analysis of the generalized vicinity of a large earthquake. The differences between physical mechanisms generating earthquakes at different depths have been taken into account. We use data from the regional catalog for Kamchatka and the North Kuril Islands compiled by the KB FRC UGS RAS to discuss the question of how frequently such typical average anomalies are statistically reliably identified in the foreshock areas of individual large earthquakes. For this catalog at least one typical anomaly has been identified in the third of all cases where target М6.5+ earthquakes are concerned. The likelihood of successful retrospective prediction is critically dependent on the number of events recorded in the foreshock area of the large earthquake in question. The increase in the fraction of retrospectively predicted earthquakes with increasing number of events in the foreshock area of a large earthquake is supported by an analysis of data from worldwide ISC-GEM and GCMT catalogs and the double Turkish earthquakes of 2023. Options are suggested to further develop this prediction method, and attention is drawn to the problem of false alarms.

A review is presented summarizing the work done in the search for earthquake precursors in Kamchatka compared with the leading elements of seismicity in the territory during the period of detailed seismic observation, 1962–2022, namely, the cumulative plot of seismic energy release and the large earthquakes that have occurred in the region. One peculiarity of the observing network consists in the location of most “nonseismological” types of precursor observation in the restricted area of the Petropavlovsk-Kamchatsky Test Site (PKTS). An analysis of 14 types of seismic, geophysical, and geochemical precursors preceding seven shallow and medium-depth earthquakes of 2005–2022 with М_W = 6.6–7.7 showed the growth of the number of precursors N with increasing parameter M_W/log d_h (d_h is hypocentral distance to the PKTS center in km), which characterizes the relative intensity of earthquake precursory processes in the PKTS area. This relationship between N and M_W/log d_h can be seen for interplate (subduction) earthquakes in the Kamchatka segment of the Kuril–Kamchatka island arc, is consistent with the occurrence of precursors in 1987–2004, and reflects the property of their simultaneous occurrence before earthquakes that are the largest and near to the PKTS. The effect of simultaneous occurrence of precursors (ESOP) before such earthquakes was observed in at least 80% of precursors of all those considered in this study. For such earthquakes, the ratio between hypocentral distance d_h and rupture length L (km) is d_h/L = 3.8–1.6; that is, the occurrence of ESOP is characteristic for the near and intermediate zones of the future earthquake rupture zone. Four separate kinds of precursor were examined to show that their threshold values d_h/L for the М_W ≥ 6.6 events are 5.0–8.5. If ESOP has been detected during seismic prediction work in real time, then one can use the threshold value found for it d_h/L ≤ 3.8 to considerably diminish the estimate of the distance between the future large earthquake and the PKTS and the Petropavlovsk–Elizovo urban agglomeration compared with the approach in which data on separate kinds of precursor are used.