Методика выделения информативных признаков в сигналах геоакустической эмиссии

Исследования геоакустической эмиссии в сейсмоактивном регионе на Камчатке показывают, что при подготовке землетрясений и последующей релаксации поля локальных напряжений в пункте наблюдений в геоакустических сигналах возникают ярко выраженные импульсные аномалии. Качественному выделению таких аномалий препятствуют сильное искажение и ослабление амплитуды сигнала. Обзор существующих методов анализа акустической эмиссии показывает, что чаще всего исследователи обращаются к анализу энергетических и статистических свойств сигналов, как более доступных для изучения. Отличительными особенностями предлагаемого авторами подхода являются выделение информативных признаков на основе анализа временной и частотно-временной структур геоакустических сигналов и описание многообразных форм распознаваемых импульсов ограниченным набором паттернов. Настоящее исследование открывает перспективу разработки новых методов выявления аномального поведения геоакустических сигналов, в том числе и перед землетрясениями. В работе описана методика извлечения информации из потоков импульсов геоакустической эмиссии звукового частотного диапазона. Представлена математическая модель геоакустического импульса, отражающая процесс генерации сигнала от множества элементарных источников. Приводится решение задачи выделения информативных признаков в геоакустических сигналах путем описания фрагментов сигнала матрицами отношений амплитуд локальных экстремумов и интервалов между ними. Приводится результат применения разработанного алгоритма для автоматического описания структуры выделяемых импульсов и для образования множества паттернов, характеризующих особенности сигналов геоакустической эмиссии, наблюдаемых на полевых станциях ИКИР ДВО РАН. Представлена методика сокращения размерности множества выделенных импульсов, позволяющая найти близкие по структуре паттерны. Предложено решение проблемы обработки большого потока данных путем унификации описания импульсов и их систематизации. Предлагается метод идентификации модели геоакустического импульса с использованием разреженных аппроксимационных схем. Дано алгоритмическое решение задачи понижения вычислительной сложности метода согласованного преследования, заключающееся во включении в метод алгоритма итерационного уточнения решения на каждом шаге. Результаты проведенных научных работ позволили создать инструмент для исследования динамических свойств сигналов геоакустической эмиссии в интересах разработки детекторов предсказания землетрясений

Estimation of the power of geoacoustic emission sources registered in Mikizha Lake, Kamchatka region

A method for estimating the power of geoacoustic emission sources recorded by a combined hydroacoustic receiver in Mikizha lake (Kamchatka region) is proposed. The results of the method application at different stages of seismic activity are presented

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

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

Methods for spatial direction finding of geoacoustic signals at Mikizha Lake in Kamchatka

In the framework of the work, a spatial analysis of geoacoustic emissions properties recorded by a hydroacoustic receiver in a shallow Mikizha Lake, Kamchatkskiy kray, is carried out. The features of geoacoustic pulse registration are considered, methods to determine the directions of their arrival and to locate the sources are proposed. Examples of geoacoustic signals during background periods and seismic event preparation periods are presented

Changes of geoacoustic emission directivity at «Mikizha» site associated with earthquakes in Kamchatka

To investigate high frequency geoacoustic emission, a receiving system based on a compound vector receiver was installed in Kamchatka. It allows the authors to determine the direction of sound wave arrival. In the result of data analysis for the period from August 2008 to January 2016, it was determined that anomalies of geoacoustic emission directivity occur during the majority of the earthquakes with Ks > 9.0 in the South of Kamchatka

Changes of geoacoustic emission directivity at «Mikizha» site associated with earthquakes in Kamchatka

To investigate high frequency geoacoustic emission, a receiving system based on a compound vector receiver was installed in Kamchatka. It allows the authors to determine the direction of sound wave arrival. In the result of data analysis for the period from August 2008 to January 2016, it was determined that anomalies of geoacoustic emission directivity occur during the majority of the earthquakes with Ks > 9.0 in the South of Kamchatka

Adaptive Approach to Time-Frequency Analysis of AE Signals of Rocks

The paper describes a new adaptive approach to the investigation of acoustic emission of rocks, the anomalies of which may serve as short-term precursors of strong earthquakes. The basis of the approach is complex methods for monitoring acoustic emission and for analysis of its time-frequency content. Piezoceramic hydrophones and vector receivers, installed at the bottom of natural and artificial water bodies, as well as in boreholes with water, are used as acoustic emission sensors. To perform a time-frequency analysis of geoacoustic signals, we use a sparse approximation based on the developed Adaptive Matching Pursuit algorithm. The application of this algorithm in the analysis makes it possible to adapt to the concrete characteristics of each geoacoustic pulse. Results of the application of the developed approach for the investigation of acoustic emission anomalies, occurring before earthquakes, are presented. We analyzed the earthquakes, that occurred from 2011 to 2016 in the seismically active region of the Kamchatka peninsula, which is a part of the circum-Pacific orogenic belt also known as the “Ring of Fire”. It was discovered that geoacoustic pulse frequency content changes before a seismic event and returns to the initial state after an earthquake. That allows us to make a conclusion on the transformation of acoustic emission source scales before earthquakes. The obtained results may be useful for the development of the systems for environmental monitoring and detection of earthquake occurrences

Complex analysis of pre-seismic geoacoustic and electromagnetic emission signals

The article describes the results of complex analysis of pre-seismic signals of electromagnetic and geoacoustic radiation. We analyzed the frequency content of single sferics and geoacoustic impulses recorded before the Zhupanov earthquake that occurred on January 30, 2016. The signals were analyzed using sparse approximation method, in particular Adaptive Matched Pursuit. Background signals were studied together with pre-seismic ones. Distributions of frequencies, that are part of background and pre-seismic signals, were compared. Differences in the frequency content of pre-seismic sferics and geoacoustic impulses were found. The revealed features of pre-seismic signals in the future can be used in the design of systems for monitoring, forecasting and prevention of natural disasters. The research was supported by Russian Science Foundation (project No. 18-11-00087)

Joint perturbation of geoacoustic, emanation, and atmospheric electric fields at the boundary of the earth’s crust and the atmosphere before an earthquake

The possibility of joint perturbation of geoacoustic, emanation and atmospheric electric fields by the Earth’s crust — atmosphere boundary before an earthquake is considered. In order to detect it, simultaneous registration of these fields was carried out in Kamchatka in August–October 2012. Synchronous anomalous disturbances were recorded 13 days before an earthquake with the magnitude Mw = 5.6 at the distance of 140 km from an epicenter. It may be considered to be a complex short-term precursor

Overview of processing and analysis methods for pulse geophysical signals

The paper discusses the processing and analysis methods for the geoacoustic and electromagnetic emission pulse signals recorded for more than 20 years at the IKIR FEB RAS geodynamic proving ground (Kamchatka Peninsula). The methods for pulse detection, waveform reconstruction, pulse time-frequency analysis using adaptive sparse approximation, structural description of pulse waveforms and pulse classification are proposed. To detect pulses, the adaptive threshold scheme is used. It adjusts to the noise level of a processed signal. To analyze time-frequency structure of the pulses, the adaptive matching pursuit algorithm is used. To identify pulse waveform, the structural description method is proposed. It encodes pulses with special image matrices. The method of the identified pulses classification is considered. Since the methods for pulse structure analysis are sensitive to noise and distortions, the authors propose the method for pulse waveform reconstruction based on wavelet filtering. The geophysical signal information features determined during the analysis can be used to search for anomalies in the data, and then establish a relationship between these anomalies and deformation process dynamics, in particular, with earthquake development processes