Journal of Volcanology and Seismology最新文献

The results of instrumental observations carried out at observatories of the INTERMAGNET network and at the Wakkanai ionospheric sounding station were used to show that the vigorous effusion–explosion eruption of Shiveluch Volcano occurring on April 10, 2023 was accompanied by variations in the Earth’s magnetic field, as well as by changes in the critical frequency of the ionospheric F 2 layer.

This paper presents new petrogeochemical data concerning rocks sampled on the Outer Islands in the Gulf of Finland. Earlier, quartz porphyries on Hogland Island were regarded as the standard for volcanic comagmates of rapakivi granites in the Wyborg massif. Sommers Island was found to contain two effusive rock sequences. The “southern” sequence is composed of quartz porphyries whose isotopic age is 1.66 Ga, so they can be regarded as the earliest manifestations of Riphean magmatic activity in the area. The “northern” rock sequence contains, apart from quartz porphyries, also trachybasalts, basaltic andesites, and dacites; the sequence has an isotopic age is 1.59‒1.57 Ga, which is inconsistent with the figures for the adjacent Wyborg massif (1.65‒1.63 Ga). For this reason, in spite of the fact that quartz porphyries and rapakive granites have similar compositions, the volcanics did not result from differentiation of the magma that has produced the granites, but were formed independently of these from a source of the same type which however was in a slightly different structural setting that allowed their free supply onto the ground surface.

OBS observations in the Persian Gulf during a short time span have revealed the occurrence of low magnitude (M_L = –0.2–2.9) earthquakes with hypocenters in the mantle beneath the Gulf and beneath the Zagros Mountain Massif. A cross-section across the shoreline of the Persian Gulf shows the projections of these hypocenters beneath the Zagros Mountains to make inclined layers that dip northeast at a high angle into the mantle down to depths of 120‒180 km. The 3D distribution of large and moderate magnitude earthquakes based on an improved earthquake catalog as reported by the US Geological Survey and by the International Seismological Centre (ISC) is not at variance with the distribution of microearthquakes and low magnitude earthquakes but seems rather to supplement it, forming a separate seismic dipping layer. According to the data acquired by OBS observations, seismic activity occurs throughout the entire crust and upper mantle of the region rather than in the upper crustal layers only as was asserted in previous publications. It is possible that collision and accompanying phenomena (mantle seismicity and destruction of the granitic layer in the crust) are related to the hypothetical rotation of the Earth around the center of rotation placed at Cyprus Island.

This paper reports results from an analysis of swarm seismic events that were recorded in 2018 in the area of the Elbrus Volcanic Center (EVC) by the North Caucasus Seismological Network of the Federal Research Center, Geophysical Survey, Russian Academy of Sciences (FRC GS RAS). The standard location procedure was used to find the hypocenters of recorded events in the EVC area. In the LOS program package, a complex combined location algorithm, methods for minimizing the time residuals at the source, and search over a grid with several trial depth values, were used to relocate the hypocenters of seismic events in swarm sequences. This approach enhances location reliability due to incorporation of the uncertainties related to erroneous onset identification and insignificant deviations of travel times that depend on the earth velocity model used here. A study of earthquake mechanisms for the larger earthquakes has determined the type of slip in agreement with the kinematics in the Elbrus–Mineralnye Vody normal-oblique fault zone. Correlation analysis of waveforms on the vertical component that have been filtered in the frequency range 1‒10 Hz, which includes P and S waves, at the nearest station shows a high agreement among the data under analysis (the correlation coefficient is R ≥ 0.85), thus indicating a high probability of all events having similar sources and propagation paths of seismic waves. Comparison of power spectral densities for individual earthquakes in the swarm sequences also demonstrates a high similarity.

This paper describes the behavior of several seismic precursors prior to the 2016–2019 activation in an area of a complex geodynamic setting at the boundary of the Pacific, North American, and Eurasian plates. We used an integrated approach to combine identified precursors with a view to getting more accurate locations of possible rupture zones of future large earthquakes. The precursors include quiescence based on the RTL parameter and the “Z-function”, variations in the slope of the earthquake recurrence graph (γ-value), and the areas of seismic ruptures dS. For the first time in Kamchatka, we analyze anomalies in the parameter dS interpreted as seismic activations to show the presence of a precursory component before the onset of the foreshock activation. Examples include increases in the values of that parameter before events that were the largest for the areas where they occurred: the Near-Islands Aleutian earthquake of July 17, 2017, M_w = 7.8 and the Uglovoe Podnyatie earthquake of December 20, 2018, M_w = 7.3. The overall extent of the anomalous area, which still exists and includes consecutive quiescence and foreshock phases, is ~900 km, which creates conditions for possible occurrence of a new great earthquake in the junction zone of the three plates with a magnitude that can exceed whatever has been recorded in the region so far.