SEASONAL PERIODICITY AND NOISE DISCRIMINATION OF MICROEARTHQUAKES AT THE GARM TEST AREA
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences
Journal: Problems of Engineering Seismology
Tome: 48
Number: 2
Year: 2021
Pages: 24-46
UDK: 550.34
DOI: 10.21455/VIS2021.2-2
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DESHCHEREVSKII A.V., ZHURAVLEV V.I., LUKK A.A., SIDORIN A.Y. SEASONAL PERIODICITY AND NOISE DISCRIMINATION OF MICROEARTHQUAKES AT THE GARM TEST AREA // . 2021. Т. 48. № 2. С. 24-46. DOI: 10.21455/VIS2021.2-2
@article{DESHCHEREVSKIISEASONAL2021,
author = "DESHCHEREVSKII, A. V. and ZHURAVLEV, V. I. and LUKK, A. A. and SIDORIN, A. Y.",
title = "SEASONAL PERIODICITY AND NOISE DISCRIMINATION OF MICROEARTHQUAKES AT THE GARM TEST AREA",
journal = "Problems of Engineering Seismology",
year = 2021,
volume = "48",
number = "2",
pages = "24-46",
doi = "10.21455/VIS2021.2-2",
language = "English"
}
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Keywords: microseismic noise, microearthquakes, time series, seasonal periodicity, antiphase of noise and the number of microearthquakes, noise discrimination
Аnnotation: We studied the time series of the number of the weakest earthquakes (microearthquakes) with a magnitude of M £ 2, recorded by 15 seismic stations of the Garm test area in 1975-1985, and the level of microseismic noise at different frequencies in the range from about 0.005 to 50 Hz, recorded by the Garm station of the IRIS observation network for periods 2006-2009 and 2013-2019. The main goal of the research was to find a correspondence and, if possible, cause-and-effect relationships between quasiperiodic components present in both types of time series. Seismic events recorded by less than 4 stations and not included in the main earthquake catalog due to the impossibility of reliable determination of their hypocentral parameters were used as microearthquakes. At each station, only the number of such events per day was recorded. To identify stable periodicities, all series were studied using spectral and periodogram analysis methods, adapted to work with non-stationary signals. The original data series were analyzed, as well as their regularized variants (logarithms and ranks of the number of events). Regularization made it possible to reduce the contribution of non-stationary effects (random bursts of activity, an increase in the number of microearthquakes during periods of aftershock series, etc.) and ensured robustness of the results. As a result of the analysis, it was found that of all possible rhythms common for the two types of time series, only the seasonal one is significant. The seasonal rhythm of microseismic noise at different frequency channels differs in phase and amplitude. High-frequency noise (channels of the IRIS system with a central frequency from 1 to 47 Hz), falling into the frequency range of the measuring and recording channels of the seismic stations of the Garm test area, is in antiphase with the seasonal variation in the number of registered microearthquakes at all stations, with some specificity for individual stations. The antiphase change in the number of registered microearthquakes and the level of microseismic noise in the recording band of seismic stations suggests that the reason for these changes is due to the noise discrimination of microearthquakes when they are identified on seismograms.