scholarly journals On Possible Electromagnetic Precursors to a Significant Earthquake (Mw = 6.3) Occurred in Lesvos (Greece) on 12 June 2017

Entropy ◽  
2019 ◽  
Vol 21 (3) ◽  
pp. 241 ◽  
Author(s):  
Stelios Potirakis ◽  
Alexander Schekotov ◽  
Yiannis Contoyiannis ◽  
Georgios Balasis ◽  
Grigorios Koulouras ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Statistical Methods ◽  
Focal Depth ◽  
Low Frequency ◽  
Electromagnetic Emission ◽  
Magnetic Field Data ◽  
Magnetometer Array ◽  
Natural Time ◽  
Electromagnetic Precursors ◽  
Criticality Analysis

This paper reports an attempt to use ultra-low-frequency (ULF) magnetic field data from a space weather monitoring magnetometer array in the study of earthquake (EQ) precursors in Greece. The data from four magnetometer stations of the HellENIc GeoMagnetic Array (ENIGMA) have been analyzed in the search for possible precursors to a strong EQ that occurred south of Lesvos Island on 12 June 2017, with magnitude Mw = 6.3 and focal depth = 12 km. The analysis includes conventional statistical methods, as well as criticality analysis, using two independent methods, the natural time (NT) method and the method of critical fluctuations (MCF). In terms of conventional statistical methods, it is found that the most convincing ULF precursor was observed in the data of ULF (20–30 mHz) depression (depression of the horizontal component of the magnetic field), which is indicative of lower ionospheric perturbation just 1 day before the EQ. Additionally, there are indications of a precursor in the direct ULF emission from the lithosphere 4 days to 1 day before the EQ. Further study in terms of NT analysis identifies criticality characteristics from 8 to 2 days before the EQ both for lithospheric ULF emission and ULF depression, while MCF reveals indications of criticality in all recorded magnetic field components, extending from 10 to 3 days before the EQ. Beyond the recordings of the geomagnetic stations of ENIGMA, the recordings of the fracto-electromagnetic emission stations of the HELlenic Seismo-ElectroMagnetics Network (ELSEM-Net) in Greece have been analyzed. The MHz recordings at the station that is located on Lesvos Island presented criticality characteristics (by means of both NT analysis and MCF) 11 days before the EQ, while a few days later (7–6 days before the EQ), the kHz recordings of the same station presented tricritical behavior. It is noted that the magnetosphere was quiet for a period of two weeks before the EQ and including its occurrence.

scholarly journals Comment on "Ultra low frequency (ULF) electromagnetic anomalies associated with large earthquakes in Java Island, Indonesia by using wavelet transform and detrended fluctuation analysis" by Febriani et al. (2014)

2015 ◽  
Vol 15 (12) ◽  
pp. 2697-2701 ◽  
Author(s):  
F. Masci ◽  
J. N. Thomas
Keyword(s):  
Magnetic Field ◽  
Detrended Fluctuation Analysis ◽  
Field Data ◽  
Low Frequency ◽  
Fluctuation Analysis ◽  
Geomagnetic Disturbances ◽  
Magnetic Field Data ◽  
Seismic Origin ◽  
Detrended Fluctuation ◽  
Large Earthquakes

Abstract. We examine the recent report of Febriani et al. (2014) in which the authors show changes in ULF magnetic field data prior to the M7.5 Tasikmalaya earthquake that occurred south of Java, Indonesia, on 2 September 2009. Febriani et al. (2014) state that the magnetic changes they found may be related to the impending earthquake. We do not agree that the pre-earthquake magnetic changes shown in Febriani et al. (2014) are seismogenic. These magnetic changes, indeed, are too closely related to global geomagnetic disturbances to be regarded as being of seismic origin.

scholarly journals Comment on "Ultra low frequency (ULF) electromagnetic anomalies associated with large earthquakes in Java Island, Indonesia by using wavelet transform and detrended fluctuation analysis", by Febriani et al. (2014)

2015 ◽  
Vol 3 (9) ◽  
pp. 5665-5675 ◽  
Author(s):  
F. Masci ◽  
J. N. Thomas
Keyword(s):  
Magnetic Field ◽  
Detrended Fluctuation Analysis ◽  
Field Data ◽  
Low Frequency ◽  
Activity Level ◽  
Fluctuation Analysis ◽  
Magnetic Field Data ◽  
Seismic Origin ◽  
Detrended Fluctuation ◽  
Large Earthquakes

Abstract. We examine the recent report of Febriani et al. (2014) where the authors show changes in ULF magnetic field data prior to the M7.5 Tasikmalaya earthquake occurred south of Java, Indonesia, on 2 September 2009. Febriani et al. (2014) state that the magnetic changes they found may be related to the impending earthquake. We do not agree that the preearthquake magnetic changes shown in Febriani et al. (2014) are seismogenic. These magnetic changes, indeed, are too closely related to the global geomagnetic activity level to be regarded as being of seismic origin.

scholarly journals Low-frequency Waves due to Newborn Interstellar Pickup He+ Observed by the Ulysses Spacecraft

2021 ◽  
Vol 923 (2) ◽  
pp. 185
Author(s):  
Anastasia V. Marchuk ◽  
Charles W. Smith ◽  
Abigale S. Watson ◽  
Matthew R. Argall ◽  
Colin J. Joyce ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Data ◽  
Low Frequency ◽  
Wave Excitation ◽  
Pickup Ions ◽  
Magnetic Field Data ◽  
Ion Production ◽  
Background Turbulence ◽  
The Waves ◽  
Low Frequency Waves

Abstract We have surveyed magnetic field data from the Ulysses spacecraft and found examples of magnetic waves with the expected characteristics that point to excitation by newborn pickup He+. With interstellar neutrals as the likely source for the pickup ions, we have modeled the ion production rates and used them to produce wave excitation rates that we compare to the background turbulence rates. The source ions are thought to be always present, but the waves are seen when growth rates are comparable to or exceed the turbulence rates. With the exception of the fast latitude scans, and unlike the waves excited by newborn interstellar pickup H+, the waves are seen throughout the Ulysses orbit.

scholarly journals On ion gyro-harmonic structuring in the stimulated electromagnetic emission spectrum during second electron gyro-harmonic heating

2012 ◽  
Vol 30 (11) ◽  
pp. 1587-1594 ◽  
Author(s):  
A. Samimi ◽  
W. A. Scales ◽  
P. A. Bernhardt ◽  
S. J. Briczinski ◽  
C. A. Selcher ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
Electromagnetic Emission ◽  
Spectral Lines ◽  
Critical Parameters ◽  
Pump Field ◽  
Pump Frequency ◽  
Ionospheric Heating ◽  
Background Magnetic Field ◽  
Stimulated Electromagnetic Emission

Abstract. Recent observations show that, during ionospheric heating experiments at frequencies near the second electron gyro-harmonic, discrete spectral lines separated by harmonics of the ion-gyro frequency appear in the stimulated electromagnetic emission (SEE) spectrum within 1 kHz of the pump frequency. In addition to the ion gyro-harmonic structures, on occasion, a broadband downshifted emission is observed simultaneously with these spectral lines. Parametric decay of the pump field into upper hybrid/electron Bernstein (UH/EB) and low-frequency ion Bernstein (IB) and oblique ion acoustic (IA) modes is considered responsible for generation of these spectral features. Guided by predictions of an analytical model, a two-dimensional particle-in-cell (PIC) computational model is employed to study the nonlinear processes during such heating experiments. The critical parameters that affect the spectrum, such as whether discrete gyro-harmonic on broadband structures is observed, include angle of the pump field relative to the background magnetic field, pump field strength, and proximity of the pump frequency to the gyro-harmonic. Significant electron heating along the magnetic field is observed in the parameter regimes considered.

scholarly journals Statistical Significance of Earth’s Electric and Magnetic Field Variations Preceding Earthquakes in Greece and Japan Revisited

Entropy ◽  
2018 ◽  
Vol 20 (8) ◽  
pp. 561 ◽  
Author(s):  
Nicholas Sarlis
Keyword(s):  
Magnetic Field ◽  
Statistical Significance ◽  
Low Frequency ◽  
Lead Times ◽  
Operating Characteristics ◽  
Complexity Measures ◽  
Natural Time ◽  
Experimental Findings ◽  
Precursory Phenomena ◽  
Magnetic Field Variations

By analyzing the seismicity in a new time domain, termed natural time, we recently found that the change of the entropy under time reversal (Physica A2018, 506, 625–634) and the relevant complexity measures (Entropy2018, 20, 477) exhibit pronounced variations before the occurrence of the M8.2 earthquake in Mexico on 7 September 2017. Here, the statistical significance of precursory phenomena associated with other physical properties and in particular the anomalous variations observed in the Earth’s electric and magnetic fields before earthquakes in different regions of the world and in particular in Greece since 1980s and Japan during 2001–2010 are revisited (the latter, i.e., the magnetic field variations are alternatively termed ultra low frequency (ULF) seismo-magnetic phenomena). Along these lines we employ modern statistical tools like the event coincidence analysis and the receiver operating characteristics technique. We find that these precursory variations are far beyond chance and in addition their lead times fully agree with the experimental findings in Greece since the 1980s.

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