Analysis of VLF Signal Noise Changes in the Time Domain and Excitations/Attenuations of Short-Period Waves in the Frequency Domain as Potential Earthquake Precursors

Nina, Aleksandra

doi:10.3390/rs16020397

Cited by 1 publication

(12 citation statements)

References 31 publications

(59 reference statements)

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“…This also applies to other analyses in which this parameter is used. In the case of an error in the determination of T, there are two cases that depend on the values of T. This explanation is given in [30] and is based on the fact that by applying the FFT to data recorded at equidistant time intervals, equidistant values of f are obtained.…”

Section: Discussionmentioning

confidence: 99%

“…As in previous analyses of excitations and attenuations of small-period waves in the time intervals around the considered earthquakes [27,29,30], we examined the changes in the amplitude characteristics of the VLF signal emitted by the ICV transmitter located in Isola di Tavolara, Sardinia, Italy (40.92 N, 9.73 E) and received by the Absolute Phase and Amplitude Logger (AbsPAL) receiver in Belgrade, Serbia (44.8 N, 20.4 E). The ICV transmitter emits at 20.27 kHz with a power of 20 kW.…”

Section: Observationsmentioning

confidence: 99%

“…The investigation of the excitations and attenuations of small-period waves by processing the amplitude of the VLF signal in this study is based on the procedures applied in previous relevant studies [27,28,30]. For this reason, we only list the main features of these procedures in this section.…”

Section: Data Processingmentioning

confidence: 99%

“…In the frequency domain, the analysis of the Fourier amplitude obtained by applying the fast Fourier transform (FFT) to the time evolutions of the signal amplitude and phase shows its increases at discrete low values of wave periods and its decreases at other, also low-value, wave periods. The first investigations of these changes in signal characteristics have been published in several studies [27][28][29][30][31]. One of the basic conclusions is that it is possible to connect several earthquakes that occur in a short time interval in some localised area with one change in the signal, i.e., that several events occur during one continuous disturbance.…”

Section: Introductionmentioning

confidence: 99%

“…The focus of the analysis is on the eight-day period from 26 October to 2 November 2016. Here, we use the same methods as those described in the studies of earthquakes that occurred during periods without intense seismic activity (PWISA) [27,30]. In addition, the daily values of the parameters relevant to the study during a one-month interval (10 October-10 November 2016) are presented in order to determine the beginnings and endings of the observed changes.…”

Section: Introductionmentioning

confidence: 99%

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VLF Signal Noise Reduction during Intense Seismic Activity: First Study of Wave Excitations and Attenuations in the VLF Signal Amplitude

Nina

2024

Remote Sensing

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This study is a continuation of pilot research on the relationships between seismic activity and changes in very low frequency (VLF) signals starting a few minutes or a few dozen minutes before an earthquake. These changes are recorded in the time and frequency domains and their duration can be influenced not only by the strongest earthquake but also by others that occur in a short time interval. This suggests that there are differences in these changes in cases of individual earthquakes and during the period of intense seismic activity (PISA). In a recent study, they were validated in the time domain by comparing the amplitude noise reductions during the PISA and before earthquakes that occurred in the analysed periods without intense seismic activity (PWISA). Here, we analyse the changes in the VLF signal amplitude in the frequency domain during the PISA and their differences are compared to the previously investigated relevant changes during PWISA. We observe the signal emitted by the ICV transmitter in Italy and received in Serbia from 26 October to 2 November 2016 when 907 earthquakes occurred in Central Italy. The study is based on analyses of the Fourier amplitude AF obtained by applying the fast Fourier transform (FFT) to the values of the ICV signal amplitude sampled at 0.1 s. The obtained results confirm the existence of one of the potential earthquake precursors observed during PWISA: significantly smaller values of AF for small wave periods (they can be smaller than 10−3 dB) than under quiet conditions (the expected values are larger than 10−2 dB). Exceptions were the values of AF for wave periods between 1.4 s and 2 s from a few days before the observed PISA to almost the end of that period. They were similar or higher than the values expected under quiet conditions. The mentioned decrease lasted throughout the observed longer period from 10 October to 10 November, with occasional normalisation. It was many times longer than the decreases in AF around the considered earthquakes during PWISA, which lasted up to several hours. In addition, no significant wave excitations were recorded at discrete small values of the wave periods during the PISA, as was the case for earthquakes during PWISA. These differences indicate the potential possibility of predicting the PISA if the corresponding earthquake precursors are recorded. Due to their importance for potential warning systems, they should be analysed in more detail in future statistical studies.

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Section: Discussionmentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%