Izvestiya, Physics of the Solid Earth最新文献

Before the 15 strongest earthquakes in California with magnitudes (M geqslant 6.5) from 1984 to 2023, an analysis of seismicity anomalies was conducted using two parameters: the b-value and the RTL function. Spatiotemporal anomalous areas were identified based on known precursors for these parameters. The values of tuning coefficients for the calculation algorithms and catalog filtering parameters selected for the analysis of each earthquake are presented. Characteristics of the anomalies were determined, including their duration, size, and distance from the center of the anomaly to the earthquake epicenter. A comparison of anomaly durations revealed that, for most earthquakes, RTL parameter anomalies occur earlier than b-value anomalies. This sequence of anomaly occurrence differs from the sequence found by the authors previously when analyzing strong earthquakes in subduction zones and rift zones. A significant portion of the earthquakes studied in California occur with a delay of several months after the completion of the bay-like anomalies of the RTL parameter, which reflect the end of the formation of a metastable region in the medium. Meanwhile, abnormally low values of b-value persist until the moment of the earthquake.

Previously conducted numerical studies of the influence of class X solar flares on seismic activity have shown that the absorption of X-ray radiation from a solar flare in the ionosphere can cause pulsations of the geomagnetic field up to 100 nT and the corresponding generation of telluric currents in faults in the Earth’s crust with a density of up to 10^–6 A/m², which is comparable to the current density created in the Earth’s crust by artificial pulse sources and leading to the initiation of weak earthquakes in the Pamirs and Northern Tien Shan. To verify these numerical results, an analysis was conducted of the possible impact of the 50 strongest class X flares (1997–2023) on both global seismic activity and earthquake-preparation zones located only on the illuminated part of the globe. The method of superimposing epochs has established an increase in number of earthquakes M ≥ 4.5 within 10 days after a solar flare, especially in the area with a radius of 5000 km around the subsolar point (up to 68% for flare class >X5), compared to the same period before it. Analysis of aftershock activity of the strong Sumatra–Andaman earthquake (M = 9.1, December 26, 2004) showed that the number of aftershocks with magnitude M ≥ 2.5 increased more than 17 times after the X10.1 class solar flare (January 20, 2005) with a delay of 7–8 days. In addition, it has been shown that solar flares of class X2.3 and M3.64, which occurred after the Darfield earthquake (M = 7.1, September 3, 2010, New Zealand), in the area of subsolar points of which the aftershock zone was located, probably caused three strong aftershocks (M6.3, M5.2, and M5.9) with the same delay of 6 days on the Port Hills fault, which is the most sensitive to external electromagnetic influences in terms of its electrical conductivity and orientation. Taking into account the concept of earthquake forecasting based on trigger effects proposed by G.A. Sobolev, the possibility is discussed of using the obtained results for short-term forecasting as additional information along with known precursors.

We present new results of geochronological, rock magnetic, paleomagnetic and paleointensity studies of the olivine gabbro dyke located at the northern part of the Murmansk craton, NE Fennoscandia (the Kola Peninsula). According to its geochemistry, petrographic and geochronology features, the dyke belongs to the 2.68 Ga dyke swarm, as confirmed by Sm-Nd mineral isochron. We find a significant difference in the rock magnetic and paleomagnetic characteristics of the central and marginal parts of the dyke, which is independently supported by petrography and geochemistry. It is shown that the rocks of the central part of the dyke retained not only their primary mineral composition, but also the primary component of the natural remanent magnetization. We use its direction to determine the 2.68 Ga virtual geomagnetic pole for the Murmansk craton: Slat = 68.64292° N, Slong = 37.7945° E, N = 41 specimens, Plat = –73.5°, Plong = 138.9°, dp/dm = 3.2°/3.4°, paleolat = –65.9°. We also obtain reliable estimates (17 samples) of the Earth’s magnetic field intensity at ca. 2.68 Ga: VDM value is found to be 1.85 × 10²² A m² corresponding to the geomagnetic field several times weaker than the present-day field.

Abstract—The paper presents the algorithm for eliminating structured noise (SN) appearing in the transient electromagnetic (TEM) response curves during correlation processing of recorded pseudo noise signals. The algorithm is based on the detection and elimination of pulses of structured noise (SNP) with energies exceeding optimal detection threshold (calculated from the TEM curve) against the background of the smoothly (slowly) varying TEM sounding signal. The method provides reliable SNP detection with high correct recognition and low false alarm rate as well the subsequent elimination of SN field from the recorded TEM curves. For automatic calculation of SNP optimal detection threshold, it is proposed to use the criterion that the noise and interference signals remaining in the TEM curve after SNP removal are maximally close to normal distribution. Selection and setting of the optimal detection threshold is performed by successive sweep through its values (from maximum to minimum) with a given step which determines the accuracy of detection threshold. The procedure of selecting the detection threshold is reduced to finding, at each step, the maximum value of the Pearson correlation coefficient between the probability density distribution functions of amplitudes of noise and interference signals remaining in TEM curve after SN removal and the calculated normal distribution. This approach has made data processing maximally automated and increased its speed, which is very important in the field work. The algorithm was tested on TEM signals recorded at Chunkurchak experimental site in the field work with electromagnetic measurement system using pseudo noise signals (EMS PNS). Application of the algorithm has significantly improved (approximately by a factor of 450) the signal to noise ratio in the TEM response curve in the interval of late times.

Abstract—Based on the data of several spaced magnetic stations, the spectrum of geomagnetic variations is studied in the range of periods from two to 40 years. Special attention is paid to spectral features in the supposed range of action of intraterrestrial processes that cause geomagnetic jerks. It is shown that the detected spectral peak in the vicinity of the period of 6.5 years aligns with the previously revealed recurrence pattern of jerks with a period of three to four years; however, this peak is absent in the spectrum of solar activity. The possible wave mechanisms of the occurrence of jerks and their 6-year quasi-periodicity caused by known types of magnetohydrodynamic waves in the liquid core of the Earth, are considered, and it is shown that they are not sufficiently convincing in reproducing observations of jerks.

Abstract—The features of potential fields characterizing the Islas Orcadas and Meteor undersea rises located in the South Atlantic are considered. The rises are located at approximately the same distance to the west and to the east from the axis of the southern segment of the Mid-Atlantic Ridge. Density modeling along the profiles intersecting the rises was carried out. The analysis of potential fields and the results of density modeling shows a generally similar structure of the crust and lithosphere of the Islas Orcadas Rise and the Meteor Rise, which supports the common nature of their formation as a result of the splitting of the lithosphere of the small Agulhas plate due to kinematic restructuring, which led to the extinction of the Agulhas Ridge and formation of the southern segment of the Mid-Atlantic Ridge. However, some features in the density structure of these rises, both along their north-south trend where the influence of hot spots on the heating of the mantle is particularly evident, and along the conjugate profiles, indicate an asymmetric structure of the rises during the initial stage of their formation.

Abstract—In many aspects, the deep fluid regime plays a key role in seismicity, aseismic deformation of the lithosphere, and ore and oil genesis processes. An informative detailed analysis of the hydrogeology of shallow fault zones is presented in (Kocharyan and Shatunov, 2024), where it is noted that little is known about the character of the fluid dynamics of deep faults. This paper focuses mainly on the challenges of describing deep fault zones and highlights a number of inconsistencies that arise in this consideration. It is shown that the difficulties inherent in such a description are largely overcome by accounting for the processes of metamorphism and associated anomalies in the physical properties of the Earth’s interior. Further refinement is given to the proposition that earthquakes occurring at different depths have different physical mechanisms.

Abstract—A source of a strong earthquake, as a rule, consists of subsources which are identified by waveform modeling. This modeling does not yield an unambiguous result. In this paper, we show an example when two significantly different focal mechanism solutions are presented for the same earthquake. In one solution, the subsources are characterized by similar faulting type, while in the other solution, the last subsource has an opposite mechanism. In (Vakarchuk et al., 2013), this discrepancy was interpreted as the realization of compensatory motion. The compensatory movements are detected not only in the subsources but also at the scale level of the source zone overall, where these movements manifest themselves in a certain regularity of the aftershock mechanisms discovered in the study of the 1970 Dagestan earthquake by Kuznetsova et al. (1976). In this paper, perhaps for the first time, compensatory movements are detected in a high-magnitude earthquake swarm lacking a pronounced main shock, which occurred in 2023 in Herat Province, Afghanistan. The results are supported by the set of the seismological and satellite interferometric data.

Abstract—The paper discusses anomalies that are observed in the electric fields above hearth deposits. Hearths are important objects for archaeological studies and are traditionally detected by the positive anomaly in magnetic induction. However, magnetic measurements are not available on every archaeological site, and burning sites are not the only sources of positive magnetic anomalies. In the 1960s, it was established that the hearths can be detected using the induced polarization method (IP), but the technique has not been developed because of the imperfection of equipment at that time. Currently, multi-electrode multichannel electromagnetic prospecting systems allow prompt assessment of the distribution of electrical properties of the object and reconstructruction of its three-dimensional geoelectric structure. In this study, we examined geoelectric anomalies from a hearth, elucidated their nature, and evaluated the possibility of using electrical resistivity tomography (ERT) method to search for such objects. By the example of the fieldwork and laboratory experiments it is shown that hearths create intense anomaly of induced polarization and are distinguished by a very low electrical resistivities. It is established that the boundaries of the burning sites are clearly expressed in the maps of normalized chargeability. To study the nature of the observed geoelectrical anomalies, we carried out X-ray phase analysis and measurements of induced polarization, electrical resistivity, and magnetic susceptibility. The results have shown that the anomaly of low electrical resistivity and the polarizability anomaly are caused by the presence in hearth material of X-ray amorphous carbon in the form of soot, but not magnetite. Application of electrical resistivity tomography combind with induced polarization measurements is recommended in the search for fireplaces in archaeological prospecting.

Abstract—Postseismic movements in the source region of the July 29, 2021 Chignik M8.2 earthquake, Alaska, are analyzed using observations from GPS sites. It is shown that the displacements are have a nature of a postseismic sliding (afterslip). The velocity of postseismic displacements of the points on the Earth’s surface (GPS sites) decreases with time by the power law close to 1/t, where t is time after the earthquake. Over an interval of two years, the magnitudes of displacements increase in time by the law of logarithmic creep. Based on the regional catalog of the Alaska earthquakes, we have analyzed the aftershocks of the Chignik earthquake. The analysis has shown that the postseismic displacements at various GPS sites are proportional to the displacements in the seismotectonic flow caused by residual displacements in the sources of aftershocks. This allows us to consider total displacements in the aftershock sources as a universal mechanism of the postseismic afterslip deformation in the source region of the Chignik earthquake.