The paper presents the first results of integrated research of the strong seismic event (Uglovoye Podnyatiye earthquake (UPE) with a magnitude of Mw=7.3) that occurred on December 20, 2018 in the junction zone between the Kuril-Kamchatka and Aleutian island arcs. The authors has provided macroseismic information about the UPE, calculated peak ground accelerations and the seismic moment tensor, and described briefly the forshock and aftershock processes, as well as summarized data on earthquake precursors. UPE was reported to be felt at distances of up to 500 km. The maximum shaking was recorded as I = 5–6 at an epicentral distance of Δ~90 km on Bering Island, where the maximum instrumental acceleration of ~60 cm/s2 was recorded. It is shown that foreshocks remote in time occurred 2 years prior to the UPE. The distinctive grouping of the aftershocks in three spatially isolated clusters characterized by different parameters of the seismicity time course is related to the long and intense aftershock process of the UPE. The strongest aftershock had magnitude ML=6.6, another 25 events corresponded to ML≥5.0. UPE was preceded by precursor anomalies in the parameters of geophysical fields and the seismic process. The authors estimated the size of the UPE rupture, the depth of the equivalent source, the magnitude of the focal slip, and the duration of the rupture. The seismic moment tensor UPE has a large non-dipole component.
The article presents the results of the study of geothermal activity zones in the south of Eastern Siberia. In order to study the deep structure of the Earth's crust in Transbaikalia, an analysis of the anomalies of the magnetic field and gravity has been carried out. The study of deep sections through the zones of known thermal springs and mud deposits resulted in an assessment of the dependence of the thermal source temperature on the depth of the feed fluid systems. An analysis of the magnetic and density sections of the south of Eastern Siberia revealed deep fluid systems and peculiarities of the hydrothermal potential in the region. Using the models of the magnetization and density distribution, the authors have constructed location schemes for the fluid systems at different depths in the earth's crust and revealed the ways of the thermofluid flows ascending to the surface. The results of the study showed that ascending migration of fluids with the least heat loss brings hydrothermal waters to the surface through vertical faults that cut the crystalline basement in the depth interval from 2 to 10 km. Based on the analysis of heterogeneity in the deep structure of the basement, a forecast of hydrothermal zones for the south of Eastern Siberia near promising mineral resources has been made.
Results of investigation of ULF electromagnetic disturbances recorded in Japan during a seismic active period are discussed.Observations were carried out at two magnetic stations located at a distance ~4 km along a geomagnetic meridian.A central zone of the seismic activity was situated ~35 km East of the magnetic stations at the depth ~3 km under sea bottom.Methodological aspects of data processing are considered in connection with large industrial noise observed in the territory of Japan.A digital filtration and spectral method were used to calculate RMS values of H, D, and Z components of magnetic variations.The data were filtered in 4 frequency ranges f 1 =0.2-2.5 Hz, f 2 =0.05-0.2Hz, f 3 =0.01-0.05Hz, and f 4 =0.002-0.0lHz for 2, 4 and 8-hours nighttime intervals of each day during the period 21.03 -02.06.1998.It is found that RMS values of raw data increase during the bursts of the seismic activity.Ratios of RMS values of Z component to the horizontal ones (Z/H, Z/D, ZIG) increase ~ 15 days before a start of the seismic active period, then the they decrease and reach their minimum at the moment of an earthquake (strongest shock Ms=5.7), followed by a smooth relaxation of these ratio values.The availability of two magnetic stations gives an opportunity to define gradients of the electromagnetic disturbances.The RMS values of the gradients and the ratios of Z component gradients to the horizontal ones are found to exhibit the same temporal evolutions as the raw data.
Abstract. Measurements of ULF electromagnetic disturbances were carried out in Japan before and during a seismic active period (1 February 2000 to 26 July 2000). A network consists of two groups of magnetic stations spaced apart at a distance of ≈140 km. Every group consists of three, 3-component high sensitive magnetic stations arranged in a triangle and spaced apart at a distance of 4–7 km. The results of the ULF magnetic field variation analysis in a frequency range of F = 0.002–0.5 Hz in connection with nearby earth-quakes are presented. Traditional Z/G ratios (Z is the vertical component, G is the total horizontal component), magnetic gradient vectors and phase velocities of ULF waves propagating along the Earth’s surface were constructed in several frequency bands. It was shown that variations of the R(F) = Z/G parameter have a different character in three frequency ranges: F1 = 0.1 ± 0.005, F2 = 0.01 ± 0.005 and F3 = 0.005 ± 0.003 Hz. Ratio R(F3)/R(F1) sharply increases 1–3 days before strong seismic shocks. Defined in a frequency range of F2 = 0.01 ± 0.005 Hz during nighttime intervals (00:00–06:00 LT), the amplitudes of Z and G component variations and the Z/G ratio started to increase ≈ 1.5 months before the period of the seismic activity. The ULF emissions of higher frequency ranges sharply increased just after the seismic activity start. The magnetic gradient vectors (∇ B ≈ 1 – 5 pT/km), determined using horizontal component data (G ≈ 0.03 – 0.06 nT) of the magnetic stations of every group in the frequency range F = 0.05 ± 0.005 Hz, started to point to the future center of the seismic activity just before the seismoactive period; furthermore they continued following space displacements of the seismic activity center. The phase velocity vectors (V ≈ 20 km/s for F = 0.0067 Hz), determined using horizontal component data, were directed from the seismic activity center. Gradient vectors of the vertical component pointed to the closest seashore (known as the "sea shore" effect). The location of the seismic activity centers by two gradient vectors, constructed at every group of magnetic stations, gives an ≈ 10 km error in this experiment.
