Studies of seismo-ionospheric correlations using anomalies in phase of very low frequency signal

Pal, Pikesh; Sasmal, Sudipta; Chakrabarti, S.

doi:10.1080/19475705.2016.1161666

Cited by 8 publications

(5 citation statements)

References 38 publications

(42 reference statements)

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“…Additionally, studies by Indian scientists have also reported shifts in TTs, and consequent increases in D VLF , before an impending EQ [47][48][49][50]. Many other statistical studies have also reported correlations between EQs and TT anomalies, with maximal shifts occurring 0-4 days prior to the main EQ event [47,[51][52][53][54][55][56][57][58]. Furthermore, some studies based on numerical simulation of the diurnal variation of the amplitude of the VLF signal, taking into consideration the characteristics of the VLF propagation path, the transmitter, and the receiver, are applied for the determination of TTs [50,59].…”

Section: Terminator Time Methods (Ttm)mentioning

confidence: 99%

Statistical and Criticality Analysis of the Lower Ionosphere Prior to the 30 October 2020 Samos (Greece) Earthquake (M6.9), Based on VLF Electromagnetic Propagation Data as Recorded by a New VLF/LF Receiver Installed in Athens (Greece)

Politis

Potirakis

Contoyiannis

et al. 2021

Entropy

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In this work we present the statistical and criticality analysis of the very low frequency (VLF) sub-ionospheric propagation data recorded by a VLF/LF radio receiver which has recently been established at the University of West Attica in Athens (Greece). We investigate a very recent, strong (M6.9), and shallow earthquake (EQ) that occurred on 30 October 2020, very close to the northern coast of the island of Samos (Greece). We focus on the reception data from two VLF transmitters, located in Turkey and Israel, on the basis that the EQ’s epicenter was located within or very close to the 5th Fresnel zone, respectively, of the corresponding sub-ionospheric propagation path. Firstly, we employed in our study the conventional analyses known as the nighttime fluctuation method (NFM) and the terminator time method (TTM), aiming to reveal any statistical anomalies prior to the EQ’s occurrence. These analyses revealed statistical anomalies in the studied sub-ionospheric propagation paths within ~2 weeks and a few days before the EQ’s occurrence. Secondly, we performed criticality analysis using two well-established complex systems’ time series analysis methods—the natural time (NT) analysis method, and the method of critical fluctuations (MCF). The NT analysis method was applied to the VLF propagation quantities of the NFM, revealing criticality indications over a period of ~2 weeks prior to the Samos EQ, whereas MCF was applied to the raw receiver amplitude data, uncovering the time excerpts of the analyzed time series that present criticality which were closest before the Samos EQ. Interestingly, power-law indications were also found shortly after the EQ’s occurrence. However, it is shown that these do not correspond to criticality related to EQ preparation processes. Finally, it is noted that no other complex space-sourced or geophysical phenomenon that could disturb the lower ionosphere did occur during the studied time period or close after, corroborating the view that our results prior to the Samos EQ are likely related to this mainshock.

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Section: Terminator Time Methods (Ttm)mentioning

confidence: 99%

Statistical and Criticality Analysis of the Lower Ionosphere Prior to the 30 October 2020 Samos (Greece) Earthquake (M6.9), Based on VLF Electromagnetic Propagation Data as Recorded by a New VLF/LF Receiver Installed in Athens (Greece)

Politis

Potirakis

Contoyiannis

et al. 2021

Entropy

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“…By this concept several other studies have also reported shifts in TTs, and consequent increases in , before an impending EQ [Ray et al, 2013;Sasmal & Chakrabarti, 2009;Sasmal et al, 2010;Chakraborty et al, 2017]. Many other statistical studies have also reported correlations between EQs and TT anomalies, with maximal shifts occurring 0-4 days prior to the EQ [Chakrabarti et al, 2005[Chakrabarti et al, , 2007[Chakrabarti et al, , 2010Ray et al, 2010Ray et al, , 2012Ray et al, , 2013Sasmal et al, 2014;Pal et al, 2017].…”

Section: Terminator Time Methods (Ttm)mentioning

confidence: 88%

Lower-ionosphere anomalies prior to strong earthquakes that occurred in north-central mainland Greece on March 2021 as revealed by multi-method analysis of VLF sub-ionospheric propagation data

Politis,

Potirakis,

Contoyiannis

et al. 2023

Annals of Geophysics

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In this work we present the multi-method analysis of very low frequency (VLF) data, acquired by the radio receiver with call name UWA, located in Athens (Greece), in the University of West Attica, focusing on two strong ( ) earthquakes (EQs) that occurred in north-central mainland Greece sequentially, on 3 and 4 March 2021, with very close epicenters. Specifically, we used the data acquired from seven VLF transmitters located in Europe, North/North-West to UWA, and their propagation paths include the specific EQs epicenters. We analyzed these data using multiple analysis methods in order to investigate for possible EQ-related anomalies, taking also into account all the other possibly ionosphere-influencing extreme events that occurred during the studied period. Especially, we applied the “nighttime fluctuation method” (NFM), as well as, the “terminator time method” (TTM) in order to reveal any statistical anomaly in the nighttime amplitude recordings of VLF sub-ionospheric propagation data within 15 days before each one examined EQs. Also, we calculated the scalogram (wavelet power spectrum over time) using Morlet mother wavelet of the same nighttime data searching for possible imprints of wave-like structures during the same time period. In terms of criticality analysis, first we applied the “natural time” (NT) analysis method to the daily-valued NFM VLF propagation quantities, and subsequently applied the “method of critical fluctuations” (MCF) to the raw nighttime amplitude VLF recordings, to check for any criticality signatures up to two weeks before the examined EQs. Taking into account all the above-mentioned analysis results, we conclude that there are multiple indications that the lower ionosphere was indeed disturbed due to the preparation processes of the above-mentioned EQs, offering different types of seismogenic indications.

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“…However, the mechanism of why the ionosphere is perturbed before an EQ, is a challenge and is poorly understood, but we show the plausible hypotheses of this LAIC process so far proposed. Emergence of lower ionospheric perturbations prior to a large EQ has already been evidenced by means of subionospheric VLF/LF propagation anomalies [129]- [137]. Because these subionospheric VLF/LF signals are known to be reflected from the lowest ionosphere (D region at day and lower E layer at night), it is already believed that the lowest ionosphere is perturbed a few days to about a week before large EQs.…”

Section: Consideration Of the Mechanism Of Ulf Depressionmentioning

confidence: 97%

“…ULF geomagnetic fluctuations depends both on the amplitude of incident wave and the parameters during their propagation in the magnetosphere/ionosphere [128]. It is not reasonable to think about the EQ effect on the equatorial plane of the magnetosphere where those pulsations are mainly generated, so it is quite natural to attribute some changes in the ground-based ULF noise to the change in the ionospheric parameter of the propagation medium as in the case of subionospheric VLF/LF (low frequency) propagation anomalies, because we already know that the lower ionosphere is definitely perturbed before major EQs [129]- [137]. Molchanov et al (2004) [120] suggested that the depression of magnetic pulsations is caused by any ionospheric disturbances before violent EQs in the following ways.…”

Section: Consideration Of the Mechanism Of Ulf Depressionmentioning

confidence: 99%

Seismogenic ULF/ELF Wave Phenomena: Recent Advances and Future Perspectives

Hayakawa¹,

Schekotov²,

Izutsu³

et al. 2023

OJER

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There has been enormous progress in the field of electromagnetic phenomena associated with earthquakes (EQs) and EQ prediction during the last three decades, and it is recently agreed that electromagnetic effects do appear prior to an EQ. A few phenomena are well recognized as being statistically correlated with EQs as promising candidates for short-term EQ predictors: the first is ionospheric perturbation not only in the lower ionosphere as seen by subionospheric VLF (very low frequency, 3 kHz < f < 30 kHz)/LF (low frequency, 30 kHz < f < 300 kHz) propagation but also in the upper F region as detected by ionosondes, TEC (total electron content) observations, satellite observations, etc, and the second is DC earth current known as SES (Seismic electric signal). In addition to the above two physical phenomena, this review highlights the following four physical wave phenomena in ULF (ultra low frequency, frequency < 3 Hz)/ELF

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Studies of seismo-ionospheric correlations using anomalies in phase of very low frequency signal

Cited by 8 publications

References 38 publications

Statistical and Criticality Analysis of the Lower Ionosphere Prior to the 30 October 2020 Samos (Greece) Earthquake (M6.9), Based on VLF Electromagnetic Propagation Data as Recorded by a New VLF/LF Receiver Installed in Athens (Greece)

Statistical and Criticality Analysis of the Lower Ionosphere Prior to the 30 October 2020 Samos (Greece) Earthquake (M6.9), Based on VLF Electromagnetic Propagation Data as Recorded by a New VLF/LF Receiver Installed in Athens (Greece)

Lower-ionosphere anomalies prior to strong earthquakes that occurred in north-central mainland Greece on March 2021 as revealed by multi-method analysis of VLF sub-ionospheric propagation data

Seismogenic ULF/ELF Wave Phenomena: Recent Advances and Future Perspectives

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