Adaptive Threshold Scheme for Pulse Detection under Condition of Background Nonstationary Noise

The paper describes a new adaptive threshold scheme for detecting pulses in high-frequency signals against a background of non-stationary noise. The result of the scheme operation is to determine the pulse boundaries by comparing the signal amplitude-time parameters with the threshold. The threshold value is calculated in non-overlapping windows of fixed length and depends only on the background noise level. The detected pulses undergo additional shape checking, taking into account their characteristics. The parameters of the algorithms for detecting pulses and checking their shape can be adjusted for any type of high-frequency pulse signals. This threshold scheme is tuned to detect pulses in high frequency geoacoustic emission signals. The results of the scheme operation on an artificial signal and on fragments of a geoacoustic signal are given, a comparison is made between the proposed scheme and the previously used (outdated) one. The new threshold scheme proposed by the authors is less sensitive to the choice of the initial threshold value and it is more stable in operation. When processing 15-minute fragments of a geoacoustic signal, the new scheme correctly detects, on average, 5 times more pulses.

Estimation of Probability Distributions of Geoacoustic Signal Characteristics

The paper presents an estimation of probability distributions of geoacoustic signal characteristics. The studied signals have a pulsed nature. The ones have been recording at the geodynamic test site of the IKIR FEB RAS (Kamchatka Peninsula) for more than 20 years. To estimate the distribution of characteristics, such time intervals were determined in which histograms of the distribution did not change. The following characteristics were chosen for the estimation: maximum amplitude, the position of pulse envelope maximum, duration, filling frequency, and pulse-to-pulse interval. The obtained estimates made it possible to develop an empirical model of the geoacoustic emission signal. The model can help to test new and existing algorithms for the processing and analysis of geoacoustic signals. The paper also shows that the formalization of the selected characteristics makes it possible to search for anomalies, including those associated with seismic events, by the characteristic variations.

Determination Of Lunar-Solar Deformation Processes In The Geomedium Volume In The Conditions Of Megapolis

The paper describes a new borehole hardware-software complex designed for synchronous registration of geoacoustic emission signals, electromagnetic radiation, temperature and borehole device rotation angle. The results of regime measurements with the new equipment in megapolis conditions are shown. The analysis of the obtained data is performed. The spectral-time analysis of regime measurements of geoacoustic emission and electromagnetic radiation signals registered in the borehole at a depth of 274 m was carried out. In the spectra of signals of electromagnetic radiation and geoacoustic emission the main diurnal and semidiurnal deformation tidal processes of known physical nature were identified.

Anomalies in electromagnetic and geoacoustic emission signals

В работе рассматриваются предсейсмические аномалии сигналов электромагнитного излучения в диапазоне очень низких частот (ОНЧ) и геоакустической эмиссии, зарегистрированных на Камчатке в 2013 году. Выявлены признаки возникновения аномальных возмущений в исследуемых сигналах и особенности их проявления. Проведен совместный анализ предсейсмических аномалий в сигналах электромагнитного ОНЧ-излучения и геоакустической эмиссии методом наложения эпох. Представлены оценки вероятности возникновения таких аномалий в рассматриваемых геофизических сигналах. The paper considers pre-seismic anomalies in the signals of electromagnetic radia-tion in a very low frequency range and geoacoustic emission recorded in Kamchatka in 2013. Signs of anomaly occurrence in the studied signals and peculiarities of their manifestation were revealed. Using the epoch folding method, joint analysis of the detected pre-seismic electro-magnetic and geoacoustic anomalies was carried out. The estimates of occurrence probability for such amomalies of the considered geophysical fields are presented.

Geoacoustic emission during the passage through the Earth's crust of high-energy cosmic ray muons

The unresolved problem of traditional seismology to date is the separation from the stream of information recorded by numerous seismic sensors of a strictly defined signal about the approach of a catastrophic earthquake specific in time and space. Such a signal is usually lost against a constant background from a large number of another events. At the turn of the 1980s and 1990s, scientists from the Physics Institute and the Institute of Physics of the Earth developed a preliminary concept for a new promising direction in seismology. Using the signal from elastic vibrations in the acoustic frequency range for earthquake prediction. These signals can be generated by ionization. Ionization is formed at the moment of the passage of high-energy muons through a seismically stressed medium in the deep layers of the earth's crust. It is hoped that this method may be one way to predict earthquakes in the future.

Application of adaptive wavelet thresholding to recovery geoacoustic signal pulse waveforms

Recorded geoacoustic signals often contain noise and interference. Their appearance is caused by various reasons, e.g. of propagation environment heterogeneity, weather condition influence, human activity, etc. So, geoacoustic emission signals contain a persistent background noise that changes in intensity over time. This noise significantly distorts the geoacoustic pulse waveforms and thus complicates analysis of the signal characteristics. The article presents results of estimating the geoacoustic signal background noise. On the basis of these estimates, a method of adaptive wavelet thresholding is proposed to remove noise from the signal and recovery the single pulse waveforms. In conclusion, the results of a computational experiment are presented. They confirm effectiveness of using the chosen method for the geoacoustic signal preprocessing. The work was carried out as part of the implementation of the state task AAAA-A21-121011290003-0.

Deformation waves from distant earthquakes as a trigger mechanism for activating geodynamic processes in rock mass

The results of experimental studies with a laser strainmeter and a multichannel automated geoacoustic rock pressure control system “PROGNOZ ADS” aimed at identifying the nature of the effect of deformation waves from distant earthquakes on the geodynamic activity of the monitored rock mass are presented. The quantitative and energy characteristics of geoacoustic emission before and after the arrival of deformation waves in the controlled rock mass are analyzed. The analysis performed indicates a trigger mechanism of the influence of a distant earthquake on the geodynamic activity of the rock mass. It is noted that the direction of arrival of the deformation wave is an essential factor in the intensification of geodynamic activity in the rock mass. The experiments also revealed the characteristics of rock burst precursors when registering deformation waves in the low-frequency range.

Analysis of geoacoustic emission and electromagnetic radiation signals accompanying earthquake with magnitude Mw = 7.5

The paper is devoted to the analysis of frequency spectra and pulse waveform variety of the geoacoustic and electromagnetic signals recorded on Kamchatka Peninsula at “Karymshina” site during seismically calm and active periods. Signal pre-processing includes pulse detection and their waveforms reconstruction. A frequency spectrum is analyzed using the Adaptive Matching Pursuit algorithm. To study a variety of waveforms, each pulse is encoded by a special descriptive matrix. Then pulse classification based on similarity of the descriptive matrices is performed. Thus, a signal alphabet is formed. The authors analyzed the geophysical signals recorded before, during and after the earthquake with the magnitude Mw = 7.5 dated March 25, 2020. The obtained estimates of frequency spectra and signal alphabets are compared with the analysis results of signal recoded during the seismically calm period of March 22, 2020.

REGRESSION ANALYSIS OF THE SEISMIC AND GEOPHYSICAL PARAMETERS AND ITS APPLICATION FOR SEISMICITY STUDY OF THE TRANSCARPATHIAN REGION

The purpose of this work is to interpret the experimental data (deformation, geoacoustic and earthquake parameters) and to establish their relation with the seismicity of the Transcarpathian region using statistical (regression) analysis. The correlation of geophysical parameters is described, namely: deformation, geoacoustic emission and seismic characteristics of magnitude and energy class.For construction of the statistical (regression) model, geoacoustic and deformation data for the period of 2014, as well as data of the seismological catalog provided by the seismicity department of the Carpathian region (Subbotin Institute of Geophysics of NAS of Ukraine) were used. The statistical model of seismicity is built to analyze various geophysical parameters and to establish their relationship with each other by means of regression analysis.This interconnection will give an opportunity to understand how seismicity influences the change of various environmental parameters of the Transcarpathian region. The deformation and geoacoustic data used in the work were obtained at the mode geophysical station (MGS) "Beregove" and the observation point "Janoshi" (Transcarpathia). The basic regression analysis formulas used to construct a linear statistical model are given. According to the seismic catalog, a graph of dependence between energy class (K) and magnitude (MD) for the period 2002–2016 was constructed, which confirmed their dependence, as well as a histogram of seismic activity for the period 2002–2016, from which it follows that the largest number of events was in 2015. The tables, on which graphs of seismicity dependence on deformation and geoacoustics, are presented. The relationship between the magnitude (MI) and the offset shift (lg DP) in depth (h) is shown. Studies were conducted for different depths: 1) up to 2 km, 2) from 2–5 km, 3)5–10 km and 4) from 10 km or more. The results showed that the greater the depth, the greater the relationship between the magnitude (MI) and the offset shift (lg DP) is. Such studies are needed to identify the effect of seismicity on the change of other environmental parameters, in particular, temperature, characteristics of earthquake foci, which will allow building an existing model of seismicity of the Transcarpathian region.