Journal of Volcanology and Seismology最新文献

Areas where large shallow earthquakes can occur in the future are identified by considering characteristics of the attenuation field of short period shear waves in the lithosphere. A total of over 360 records of earthquakes at depths of 0–33 km have been processed; these earthquakes were recorded at the PET station from two regions enclosed in the coordinates 45.0°–50.5° N and 54.0°–56.5° N (for the sake of brevity these regions will be referred to in what follows as the southern and the northern region, respectively). In addition, for comparison purposes we used records of earthquakes made at the KGB station from the area between 52° and 54° N. We used a method based on the ratio of peak amplitudes of Sn and Pn waves. It was found that the overall attenuation in the lithosphere of the northern region is much greater than that for the southern. At the same time we note that the attenuation in both of these areas is below that in northeastern Japan. The relatively lower attenuation occurs in the rupture zones of the great earthquakes occurring in 1952 (M_w = 9.0) and in 1963 (M_w = 8.6), that is, at least 60 years ago in the southern region, while the higher attenuation occurs in the rupture zones of recent events, 1997 (M_w = 7.8), 2006 (M_w = 8.3), and 2018 (M_w = 7.3). These data are consistent with the previous inferences, namely, that typical large earthquakes in subduction zones occur in earth volumes with higher concentrations of fluids in the uppermost mantle. Following large and great earthquakes, deep fluids are rising during a few decades, producing a decrease in the attenuation of the uppermost mantle. We have identified zones of high attenuation where large (M_w ≥ 7.7) earthquakes occurred long ago. We hypothesize that active precursory processes are occurring in these zones (primarily in the Avacha Bay and east of it) before large earthquakes.

This paper summarizes available original data and material from the literature concerning our geological and geophysical knowledge of the Esmeralda submarine volcano situated at the Mariana island arc. An advanced study of the rocks dredged during the 4th and 5th cruises of the Vulkanolog research vessel yielded new information on silicate and trace element compositions of the rocks that compose the volcano. It was found that the volcanic edifice under study is composed of five rock types: basalts, basaltic andesites, dacites, gabbro, and basanites. For the first time we recovered samples of dacite and basanite that provide evidence of a broader petrochemical diversity of the Esmeralda submarine volcano compared to what has been thought previously. All dredged rocks show slightly higher concentrations of incoherent elements LILE and HFSE. Our studies enable us to classify the bulk of the dredged rocks as belonging to the association of arc ferrous tholeiites (IAB, IAT), with the composition of a single sample of alkaline basalt (basanite) plotting in the field of alkaline oceanic island basalts (OIB, OIA). The higher concentration of iron in plagioclase phenocrysts confirms the fact that the rocks are part of the high-iron tholeiitic association.

This paper provides data on the April 11, 2023 eruption of Sheveluch Volcano. The impact of the eruption has been assessed. The directed explosion destroyed the lava dome which took over 42 years to grow. According to the data acquired just before the eruption, the lava dome had a volume of about 0.53 km³. The eruption produced a field of explosive ejecta ∼70 km² in area and 0.49 km³ in volume. The directed explosion was accompanied by pyroclastic flows which traveled for distances of 25–30 km from the volcano. The associated ashfall had a length of over 200 km. The weight of an ash sample varied between 1.2 and 43.9 kg/², depending on the distance to the volcano. The area of ash deposits (with the weight of ash samples over 50 g/m²) was about 17 thousand m², the volume of the ash deposits was 0.09 km³. Considered in relation to the total volume of ejecta (over 0.60 km³), the April 11, 2023 eruption of Sheveluch should be termed a great catastrophic eruption of this century.

This study analyzes seismicity within the shelf of the Barents Sea and the Knipovich and Gakkel ridges that surround it, and compares the spatial distribution of seismicity with the fault network as identified by seismic prospecting data. Kinematic characteristics have been obtained for the spatial migration of seismic activity. It is shown that the seismic events recorded by NORSAR, the Norwegian regional network, as occurring within the Russian part of the Barents Sea shelf make linear clusters along strike slip faults. The fault network displaces Mesozoic seismic sequences and emerges at the bottom surface by displacing Quaternary deposits. This clearly indicates a present-day age of the faults along which the linear clusters of low magnitude seismicity aligned. The computation of the total seismic moment in the space-time domain showed the presence of a seismic activity migration along short fault segments in the shelf at rates of 10.5 to 25.7 km/year. A burst of general activity in the shelf area beginning in 2012 could be noted. Comparison of the time-dependent evolution of seismic activity in the shelf to fragments of the Atlantic–Arctic Rift System suggests that the evolution is due to tectonic deformation waves that are initiated along the geodynamically active plate boundary and are propagating to the shelf at a rate of 20‒22 km/year. Another alternative, namely, that the rate of migration can reach 77 km/year, is less likely. The increase in the rate of seismic activity in the shelf after 2012 might be, not emission due to the excitation of a slow deformation wave, but rather resulted from direct triggering impact on the shelf by the Knipovich and Gakkel ridges.

Ground-based vertical ionospheric soundings were used to analyze disturbances around the maximum of the F2 layer during a vigorous eruption of Stromboli Volcano, Italy involving two explosions in July and in August 2019, as well as after the resumption of volcanic activity on October 9, 2022. Characteristics of the response of the ionosphere to these events were chosen to be variations in the critical frequency of the F2 layer as recorded at the Gibilmanna, Rome, and San Vito stations not far from the volcano (within 450 km). The results of measurement provide evidence of the effect produced in the ionosphere by acoustic-gravity waves generated by volcanic activity and producing long-lived disturbances in the ionosphere.

We studied records of vertical ground velocity near broadband seismic stations installed around the epicenter of the magnitude 9, March 11, 2011 Tohoku earthquake. The MAJO station had been recording a stable daily behavior of seismic noise during 15 years before the earthquake. The station is the nearest to the epicenter, and is at a distance of 386 km from it. In 2009 pulses were identified exceeding 10% of the daily behavior. The pulses were gradually increasing and decreasing in amplitude, and lasted a few minutes. They occurred under quiet meteorological conditions and geomagnetic activity. No pulses of this kind were recorded at stations farther than 700 km from the epicenter. It is supposed that the earthquake was preceded by movements in the lithosphere beneath Japan and in the adjacent part of the Pacific Ocean.

The Pauzhetka geothermal field was surveyed to study the mineral deposits that were formed as thermal water was discharged from well separators. We studied the compositions, structure, and geochemical properties of these sediments along the flow and in vertical cross sections of manmade “sinters”. It was found that, at the beginning of thermal water discharges, the sediments were composed of X-ray-amorphous mordenite–opal mixtures; later on, the sediments became wholly siliceous. The zeolite component of the mineral deposits determines their high sorption properties in relation to Au, Ag, Hg, As, Rb, Sr, Ba, Cs and other elements; the mordenite matrix receives sulfides of iron, silver, and copper. It is shown that the mineral deposits which were formed at the ground surface of the Pauzhetka geothermal field constitute an indicator of alkaline mineral-forming and ore-forming environment in the lower horizons of the Pauzhetka geothermal system.

This study is concerned with little-studied negative bay-like anomalies of the atmospheric electric field close to ground that are recorded in seismic regions, provided the weather is “fair” for observations of atmospheric electricity. The results from observations of these anomalies have been summarized and analyzed; we have identified some features in their occurrence which provide evidence of a relationship to the deformation of near-ground rocks during the tectonoseismic process. We are using the theory of atmospheric electricity to discover the responsible source; this is a local negative space charge of small ions produced in the near-surface air under the influence of a negative vertical gradient of conductivity. It was found that the charge and the negative electric anomalies it generates have a deformation-emanation nature. We suggest a scheme for the generation of such anomalies; the roles of radon and thoron are discussed. It was found that thoron is occasionally more important than radon.

The Chuya earthquake of 2003 exerted an appreciable influence on the seismicity of the entire Altai. This paper presents data on variations in the Altai seismicity from 2003 to 2021. It is shown that earthquakes of the first half-year after the major earthquake of 2003 had their rupture zones in the epicentral zone, while the other Altai structures were aseismic. After 2009 we saw changes both in the near zone that encompasses geological structures that were adjacent to the epicenter (with distances of 60‒80 km from the mainshock epicenter), such as the Aigulak, Kurai, South Chuisky and North Chuisky mountain ranges, and in the far zone at distances of 250‒450 km from the epicenter and in different directions from it. The Aigulak earthquake of 2019 gave rise to an aftershock process that displaced the center of Altai seismicity to the eponymous mountain range. There are no data on large earthquakes during the historical period for many Altai structures which have been activated following the Chuya earthquake, either from seismological or from paleo-geological evidence. One could explain the evolution of seismicity around the rupture zone of the Chuya earthquake in space, and with time delays of some years, invoking the influence of a large earthquake on a medium involving plasticity. We know of nonlinear models that hold promise for future research concerning the influence of large earthquakes on the evolution of seismicity in geological media.

Structural-geomorphological and paleoseismological methods were used to study morphostructures on the southern slope of the Kungei Ala-Too mountain range and in its southern foothills (adyrs). An analysis of radioisotope dates (radiocarbon and infrared luminescence) in paleoseismological trenches shows a lateral migration of vigorous seismic activity along the Kultor fault zone in the northern Issyk-Kul region. It has been confirmed that the contemporary high seismic activity concentrates in the adyr zone, and is confined to adyr faults. At least seven morphogenic earthquakes have occurred along this fault zone during Holocene time. The repeat time of morphogenic earthquakes was 200‒300 years in our era. It seems that this fault generated great seismic disasters with М ~ 7.5 (Io = Х) in the 7th and 15th centuries, with the rupture zones emerging at the surface and producing fault scarps up to 70‒80 km in length.