The paper presents an analysis of phase and amplitude variations of subionospheric VLF/LF radio signals on mid-latitude routes JJY–PTK, NML–PTK, and JJI–PTK during strong and extreme magnetic storms in the periods 2000–2004 and 2021–2024. The aim of the study was to assess the impact of magnetic storms on the characteristics of signals used to monitor the lower ionosphere and search for electromagnetic precursors of natural disasters. A total of 37 magnetic storms with minimum Dst values ranging from –100 to –412 nT were analyzed. It was shown that night "bay-like" amplitude and phase disturbances are observed in cases where the main stage of the magnetic storm occurs during the local night. Such anomalies were detected in nine out of thirteen night events for the JJY signal and in some cases for the NML signal, with no effect on the JJI signal. Amplitude deviations reached 18 dB, phase deviations reached 135°. A shift in the morning and evening minima of the daily signal cycle was also established during the development of magnetic storms during the daytime and near the solar terminators. Spectral analysis showed a connection between the detected anomalies and Pi3-type geomagnetic pulsations. The obtained results are important for the correct interpretation of VLF/LF data in the search for earthquake precursors and the analysis of the ionosphere's response to tsunamis and cyclones.
This study investigates the possibility of passive monitoring of the seismoelectromagnetic effect – the generation of electromagnetic waves by seismic vibrations. The extent of its manifestation depends on the properties of the rock and pore fluid. This forms the basis for a proposed observation system for the state of the Earth's near-surface layers. An approach to data analysis is proposed, based on the method of passive seismic tomography and utilizing correlation analysis of seismic and electromagnetic noise. To evaluate the prospects of such monitoring, recordings of signals from various physical fields obtained under different conditions were examined. The results show that monitoring the electric field appears more promising compared to monitoring the magnetic field; however, it requires a substantial reduction in the noise level and improvement of signal processing methods. Reducing the measurement noise to the instrument's self-noise could potentially decrease the time required to measure the magnitude of the seismoelectric effect with high accuracy to several seconds.
The article is devoted to taking into account the difference between geodetic and normal heights of determined points in order to improve the accuracy of calculating gravity anomalies using global models of the Earth's gravity field in the form of spherical harmonics of the geopotential. The quasigeoid heights and gravity anomalies, as the most significant parameters in gravimetry, are considered as the quantities under study. Formula schemes for calculating quasigeoid heights and gravity anomalies using harmonic coefficients of the geopotential are presented. They correspond to two approaches: the traditional approach, which does not account for this height difference, and the modified approach, which does. It is shown that the modified (refined) value of the quasigeoid height is determined iteratively using the corresponding base value as an initial approximation. The modified gravity anomaly value is calculated based on the previously obtained pure gravity anomaly with subsequent reduction to the height anomaly expressed through the adjusted quasigeoid height. Calculations were performed using the EGM2008 gravity model to the 2190th degree in five 1×1 test areas located in different parts of the globe. Numerical estimates of corrections for the transition from basic to modified values were obtained. It is shown that the amplitudes of the corrections can vary from several centimeters to several decimeters for quasigeoid heights and from several microgals to 0.1 mGal and more for gravity anomalies. Since these corrections are relatively small over most of the globe, it is proposed to use an adaptive (selective) method for taking them into account. In this approach, modified values are calculated only at those points or areas where the amplitudes of the height anomalies exceed a pre-determined empirically established amplitude threshold. The amplitude threshold value is determined separately for quasigeoid heights and gravity anomalies depending on the required accuracy: the higher the accuracy requirements, the lower the threshold value, and vice versa.
An Mw 3.8 earthquake occurred in Northern Thailand (18.8365° N, 99.1133° E) on October 19, 2022 (centroid time: 21:36:33.72 UTC), within the Mae Tha Fault Zone region. Source parameters were determined through full-waveform inversion of three-component seismic data from four regional networks (TM, TH, MM, and RM). The analysis implemented a minimal 1-D velocity model with station corrections for Northern Thailand. Green's functions were calculated through frequency-wave number integration within 0.03–0.10 Hz. Moment tensor inversion yielded a predominantly strike-slip mechanism (strike = 181°, dip = 82°, rake = –179°) with 91.8% double-couple (DC) and –5.4% compensated linear vector dipole (CLVD) components. The optimal centroid depth of 4.5 km was determined through grid search analysis. Waveform analysis shows variance reduction values ranging from 0.05 to 0.74 for near-regional stations (Δ < 305 km). The focal mechanism solution and its geometric correspondence with the N–S trending segment of the Mae Tha Fault Zone indicates right-lateral strike-slip displacement along this structural trend.
The paper discusses the methodological issues of regular monitoring of volcanic regions of Kamchatka using satellite radar interferometry methods. The advantages and limitations of various displacement estimation methods are analyzed with respect to different satellite data sets over the Avachinsky–Koryaksky volcanic group for the period from 2016 to 2024. The radar data varied in frequency range (L and C), acquisition geome-try (ascending and descending satellite orbit), and number of acquisitions: both short series of images with long temporal intervals between acquisitions and long series of images with short temporal intervals were considered. Based on these data, displacement fields were calculated for image pairs (DInSAR method), cumulative dis-placement fields (summation method), and average displacement velocity fields (SBAS method) over the eight-year period. The dynamics of surface displacements on volcanic slopes were analyzed using time series. It was found that the average displacement rate does not exceed ±10 mm/year, while cumulative displacements on volcanic slopes reach values of approximately ±10 cm over the eight-year period. The results obtained using different approaches are in good agreement with each other, taking into account the inherent uncertainties to each method. At the same time, for each approach there are conditions related to the climatic characteristics of Kamchatka under which it is impossible to obtain satisfactory results due to low data coherence. Therefore, monitoring must take into account local terrain characteristics, climatic conditions, and the properties of satellite systems providing radar data. It is shown that the results obtained by different methods exhibit a high correlation (0.60–0.77), indicating the reliability of the displacement field estimates. Thus, the considered interferometric methods complement each other, and their combined application makes it possible to improve the accuracy of result interpretation and to ensure verification of monitoring data.
