scholarly journals Similar behaviors of natural ELF/VLF ionospheric emissions and transmitter signals over seismic Adriatic regions

2008 ◽  
Vol 8 (6) ◽  
pp. 1229-1236 ◽  
Author(s):  
M. Y. Boudjada ◽  
K. Schwingenschuh ◽  
H. K. Biernat ◽  
J. J. Berthelier ◽  
J. Blecki ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Geomagnetic Activity ◽  
Seismic Events ◽  
Electromagnetic Emissions ◽  
Vlf Emissions ◽  
Large Earthquakes ◽  
Key Parameter

Abstract. We report on the analysis of ELF/VLF emissions observed by the Instrument Champ Electrique (ICE) experiment onboard the DEMETER micro-satellite. We consider principally selected seismic events reported by Molchanov et al. (2006). These authors studied the VLF signals radiated by ground transmitters and received on board the DEMETER micro-satellite. They revealed a drop of the signals (scattering spot) connected with the occurrence of large earthquakes. In our investigations, we proceed to a spectral analysis of ICE observations with the aim to find if the natural ionospheric VLF/ELF emissions show, or not, a similar ''drop'' in the intensity as it is the case of the VLF transmitter signal. We combine our results with those of Molchanov et al. (2006), and we discuss the origin of such interesting ionospheric features in the frame of the investigation of the pre-seismic electromagnetic emissions. We show that the geomagnetic activity is a key parameter which could disturb the natural VLF ionospheric emissions, and also the transmitter signal. We find that it is not possible to conclude the presence, or not, of a preseismic effect when the Kp-index is higher than one.

scholarly journals Investigation of Pre-Earthquake Ionospheric and Atmospheric Disturbances for Three Large Earthquakes in Mexico

Geosciences ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 16
Author(s):  
Christina Oikonomou ◽  
Haris Haralambous ◽  
Sergey Pulinets ◽  
Aakriti Khadka ◽  
Shukra R. Paudel ◽  
...  
Keyword(s):  
Chemical Potential ◽  
Atmospheric Model ◽  
Satellite System ◽  
Seismic Events ◽  
Electron Content ◽  
Total Electron ◽  
Atmospheric Disturbances ◽  
Global Ionospheric Maps ◽  
Global Navigation Satellite ◽  
Large Earthquakes

The purpose of the present study is to investigate simultaneously pre-earthquake ionospheric and atmospheric disturbances by the application of different methodologies, with the ultimate aim to detect their possible link with the impending seismic event. Three large earthquakes in Mexico are selected (8.2 Mw, 7.1 Mw and 6.6 Mw during 8 and 19 September 2017 and 21 January 2016 respectively), while ionospheric variations during the entire year 2017 prior to 37 earthquakes are also examined. In particular, Total Electron Content (TEC) retrieved from Global Navigation Satellite System (GNSS) networks and Atmospheric Chemical Potential (ACP) variations extracted from an atmospheric model are analyzed by performing statistical and spectral analysis on TEC measurements with the aid of Global Ionospheric Maps (GIMs), Ionospheric Precursor Mask (IPM) methodology and time series and regional maps of ACP. It is found that both large and short scale ionospheric anomalies occurring from few hours to a few days prior to the seismic events may be linked to the forthcoming events and most of them are nearly concurrent with atmospheric anomalies happening during the same day. This analysis also highlights that even in low-latitude areas it is possible to discern pre-earthquake ionospheric disturbances possibly linked with the imminent seismic events.

scholarly journals Spectral analysis of auroral geomagnetic activity during various solar cycles between 1960 and 2014

2016 ◽  
Vol 34 (12) ◽  
pp. 1159-1164 ◽  
Author(s):  
Pieter Benjamin Kotzé
Keyword(s):  
Spectral Analysis ◽  
Geomagnetic Activity ◽  
Solar Minimum ◽  
High Speed ◽  
Solar Rotation ◽  
Pearson Correlation ◽  
Coronal Holes ◽  
Rotation Period ◽  
Period Change ◽  
Solar Cycles

Abstract. In this paper we use wavelets and Lomb–Scargle spectral analysis techniques to investigate the changing pattern of the different harmonics of the 27-day solar rotation period of the AE (auroral electrojet) index during various phases of different solar cycles between 1960 and 2014. Previous investigations have revealed that the solar minimum of cycles 23–24 exhibited strong 13.5- and 9.0-day recurrence in geomagnetic data in comparison to the usual dominant 27.0-day synodic solar rotation period. Daily mean AE indices are utilized to show how several harmonics of the 27-day recurrent period change during every solar cycle subject to a 95 % confidence rule by performing a wavelet analysis of each individual year's AE indices. Results show that particularly during the solar minimum of 23–24 during 2008 the 27-day period is no longer detectable above the 95 % confidence level. During this interval geomagnetic activity is now dominated by the second (13.5-day) and third (9.0-day) harmonics. A Pearson correlation analysis between AE and various spherical harmonic coefficients describing the solar magnetic field during each Carrington rotation period confirms that the solar dynamo has been dominated by an unusual combination of sectorial harmonic structure during 23–24, which can be responsible for the observed anomalously low solar activity. These findings clearly show that, during the unusual low-activity interval of 2008, auroral geomagnetic activity was predominantly driven by high-speed solar wind streams originating from multiple low-latitude coronal holes distributed at regular solar longitude intervals.

Near-field spectral analysis of data-integrative dynamic rupture earthquake simulations of the 1992 Landers earthquake

2020 ◽  
Author(s):  
Nico Schliwa ◽  
Alice-Agnes Gabriel
Keyword(s):  
Spectral Analysis ◽  
Ground Motion ◽  
Near Field ◽  
Slip Distribution ◽  
Corner Frequency ◽  
Dynamic Rupture ◽  
Geophysical Research ◽  
Acoustic Sensing ◽  
Distributed Acoustic Sensing ◽  
Large Earthquakes

<p>The rise of observations from Distributed Acoustic Sensing (e.g., Zhan 2020) and high-rate GNSS networks (e.g., Madariaga et al., 2019) highlight the potential of dense ground motion observations in the near-field of large earthquakes. Here, spectral analysis of >100,000 synthetic near-field strong motion waveforms (up to 2 Hz) is presented in terms of directivity, corner frequency, fall-off rate, moment estimates and static displacements.</p><p>The waveforms are generated in 3‐D large-scale dynamic rupture simulations which incorporate the interplay of complex fault geometry, topography, 3‐D rheology and viscoelastic attenuation (Wollherr et al., 2019). A preferred scenario accounts for off-fault deformation and reproduces a broad range of observations, including final slip distribution, shallow slip deficits, and spontaneous rupture termination and transfers between fault segments. We examine the effects of variations in modeling parameterization within a suite of scenarios including purely elastic setups and models neglecting viscoelastic attenuation. </p><p>First, near-field corner frequency mapping implementing a novel spectral seismological misfit criterion reveals rays of elevated corner frequencies radiating from each slipping fault at 45 degree to rupture forward direction. The azimuthal spectral variations are specifically dominant in the vertical components indicating we map rays of direct P-waves prevailing (Hanks, 1980). The spatial variation in corner frequencies carries information on co-seismic fault segmentation, slip distribution, focal mechanisms and stress drop. Second, spectral fall-off rates are variably inferred during picking the associated corner frequencies to identify the crossover from near-field to far-field spectral behaviour in dependence on distance and azimuth. Third, we determine static displacements with the help of near-field seismic spectra.</p><p>Our findings highlight the future potential of spectral analysis of spatially dense (low frequency) ground motion observations for inferring earthquake kinematics and understanding earthquake physics directly from near-field data; while synthetic studies are crucial to identify "what to look for" in the vast amount of data generated.</p><p><em>References:</em></p><p>Hanks, T.C., 1980. The corner frequency shift, earthquake source models and Q.</p><p>Madariaga, R., Ruiz, S., Rivera, E., Leyton, F. and Baez, J.C., 2019. Near-field spectra of large earthquakes. Pure and Applied Geophysics, 176(3), pp.983-1001.</p><p>Wollherr, S., Gabriel, A.-A. and Mai, P.M., 2019.  Landers 1992 “reloaded”: Integrative dynamic earthquake rupture modeling. Journal of Geophysical Research: Solid Earth, 124(7), pp.6666-6702.</p><p>Zhan, Z., 2020. Distributed Acoustic Sensing Turns Fiber‐Optic Cables into Sensitive Seismic Antennas. Seismological Research Letters, 91(1), pp.1-15.</p>

scholarly journals Search for anomalies in pulse flows of acoustic and electromagnetic emissions

2020 ◽  
Vol 196 ◽  
pp. 03006
Author(s):  
Yury Senkevich
Keyword(s):  
Electromagnetic Emission ◽  
Structural Features ◽  
Seismic Events ◽  
Important Research ◽  
Near Surface ◽  
Kamchatka Region ◽  
Research Task ◽  
Electromagnetic Emissions ◽  
Pulse Streams ◽  
Timely Warning

Timely warning of disasters caused by earthquakes ensures life safety. Therefore, the search for markers of pre-seismic events preceding earthquakes remains an important research task. The article presents experimental methods for assessing seismic activity in the Kamchatka region based on the results of processing and analysis of geoacoustic and electromagnetic emission signals. The research is aimed at detecting anomalies in quantitative and qualitative indicators that characterize the pulse streams of acoustic emission of near-surface rocks and electromagnetic emission in the surface layer of the atmosphere. Signal processing and analysis are carried out using special algorithms that take into account the structural features of the variety of pulse shapes and their distribution over time.

scholarly journals On the use of ELF/VLF emissions triggered by HAARP to simulate PLHR and to study associated MLR events

2022 ◽  
Vol 74 (1) ◽  
Author(s):  
Michel Parrot ◽  
Frantisěk Němec ◽  
Morris B. Cohen ◽  
Mark Gołkowski
Keyword(s):  
Spectral Analysis ◽  
Time Delay ◽  
High Frequency ◽  
Conjugate Point ◽  
Physical Processes ◽  
Line Radiation ◽  
Harmonic Radiation ◽  
Frequency Spacing ◽  
Low Altitude ◽  
Vlf Emissions

AbstractA spectrogram of Power Line Harmonic Radiation (PLHR) consists of a set of lines with frequency spacing corresponding exactly to 50 or 60 Hz. It is distinct from a spectrogram of Magnetospheric Line Radiation (MLR) where the lines are not equidistant and drift in frequency. PLHR and MLR propagate in the ionosphere and the magnetosphere and are recorded by ground experiments and satellites. If the source of PLHR is evident, the origin of the MLR is still under debate and the purpose of this paper is to understand how MLR lines are formed. The ELF waves triggered by High-frequency Active Auroral Research Program (HAARP) in the ionosphere are used to simulate lines (pulses of different lengths and different frequencies). Several receivers are utilized to survey the propagation of these pulses. The resulting waves are simultaneously recorded by ground-based experiments close to HAARP in Alaska, and by the low-altitude satellite DEMETER either above HAARP or its magnetically conjugate point. Six cases are presented which show that 2-hop echoes (pulses going back and forth in the magnetosphere) are very often observed. The pulses emitted by HAARP return in the Northern hemisphere with a time delay. A detailed spectral analysis shows that sidebands can be triggered and create elements with superposed frequency lines which drift in frequency during the propagation. These elements acting like quasi-periodic emissions are subjected to equatorial amplification and can trigger hooks and falling tones. At the end all these known physical processes lead to the formation of the observed MLR by HAARP pulses. It is shown that there is a tendency for the MLR frequencies of occurrence to be around 2 kHz although the exciting waves have been emitted at lower and higher frequencies. Graphical Abstract

scholarly journals A Review on the Mechanism of Reservoir-Induced Seismicity for Nepalese Context

2020 ◽  
Vol 19 (1) ◽  
pp. 215-221
Author(s):  
Umesh Raj Joshi ◽  
Ramesh Kumar Maskey ◽  
Kumud Raj Kafle
Keyword(s):  
Active Zone ◽  
Induced Seismicity ◽  
Seismic Events ◽  
Reservoir Induced Seismicity ◽  
The Earth ◽  
Richter Scale ◽  
Active Zones ◽  
Large Earthquakes ◽  
Storage Type ◽  
Tectonic Movements

 Over 90 cases of Reservoir Induced Seismicity have been recorded around the earth. The magnitude was varying from 3.0 to 6.3 on the Richter scale. A Reservoir Induced Seismicity (RIS) can increase the frequency of earthquakes in seismically active zones and cause a shock in seismically inactive zones. Nepal is situated in a seismically active zone with six large earthquakes of magnitude equal to or greater than 7.6. It increases the risk of RIS, while several storage-type hydropower projects are being proposed in Nepal. Seismic activities recorded around the Kulekhani-I reservoir could be a reservoir induced seismicity. However, consistent data of seismic events and reservoir levels during all phases of filling or drawing of water level is missing. This paper reviews the researches on seismic activities caused by reservoirs or tectonic movements, and the need for the study on the mechanism of RIS for the Nepalese context is identified.

Ionospheric Induction of Earthquakes: Fitting the Data

2021 ◽  
Author(s):  
Daniel Helman
Keyword(s):  
Solar Activity ◽  
Small Sample ◽  
Lower Atmosphere ◽  
Seismic Events ◽  
Petrographic Analysis ◽  
Ionospheric Disturbances ◽  
Simple Explanation ◽  
Total Electron ◽  
Ion Concentrations ◽  
Large Earthquakes

<p>This discussion assumes that there are ionospheric anomalies in total electron count (TEC) as precursors to major earthquakes. Very careful work by Thomas et al. (2017) and others remove TEC anomalies when correlated with natural events such as geomagnetic or solar activity. Without these data, correlation between ionospheric disturbances and large earthquakes (M ≥ 7.0) occurs infrequently (~20% of events) and is within the standard error resulting from the small sample size. There are two possibilities: (1) either the mechanism of volatile (including radon) release that occurs in some regions precursory to major seismic events is unrelated to ionospheric disturbances; or (2) the occurrence of these volatiles is related first to geomagnetic and solar activity. The first hypothesis is easily falsified. In addition to careful statistical analysis by Thomas et al. and others, the mechanism for travel through the lower atmosphere of matter arising on the ground as a stable electric signal is not physically plausible. The second hypothesis awaits falsification, as the correlation fits the data. If natural events such as geomagnetic and solar activity are a trigger for large earthquakes, a plausible mechanism ought to be explored. In considering the effects of ionospheric disturbances on ground-based phenomena, geomagnetically induced currents (GIC) are a reasonable model. GIC occur generally at high latitudes and are responsible for the electrocorrosion of bridges and other metal infrastructure. Fluids laden with dissolved ions occur in faults and are a potential conduit for GIC. Electromagnetic fields induced by ionospheric anomalies may be present at depth. Can these types of fields weaken earth materials? One reason dilatancy diffusion models fell out of favor is scale. The microcracks observed are too small to hold the volume of volatiles required to account for observed changes to groundwater. If instead the presence of electric and magnetic fields aid in the liberation of volatiles and dissolution of certain minerals in rock, seismic events may occur. Andrén et al. (2016), for example, note decreasing groundwater (Si and Na) ion concentrations (ratio 2:1) as well as a small decrease in Ca and an increase in K ion concentrations during a period leading up to two consecutive M > 5 earthquakes in Hafralækur, Iceland. They took well cuttings for petrographic analysis: The observed groundwater changes are consistent with contemporary replacement of labradorite with analcime and the precipitation of zeolite minerals before and during the seismic activity, respectively, when the cuttings were taken. These observations fit the data well. In some cases, solar and geomagnetic activity cause ionospheric anomalies. These then induce electromagnetic currents in faults. The resulting fields aid in the dissolution of certain minerals and release volatiles, which are then precursory to seismic events. Groundwater changes before and after such events are related to the dissolution and subsequent precipitation of minerals in the rock. This rock weakening hypothesis fits the data, and is a simple explanation for how correlations between ionospheric disturbances caused by solar or geomagnetic events and large seismic events may arise.</p>

scholarly journals Electron and ion density variations before strong earthquakes (<i>M</i>>6.0) using DEMETER and GPS data

2010 ◽  
Vol 10 (1) ◽  
pp. 7-18 ◽  
Author(s):  
M. Akhoondzadeh ◽  
M. Parrot ◽  
M. R. Saradjian
Keyword(s):  
Gps Data ◽  
Electron Content ◽  
Ion Density ◽  
Total Electron ◽  
Strong Earthquakes ◽  
Total Electron Content Data ◽  
Electromagnetic Emissions ◽  
Seismic Anomalies ◽  
Geomagnetic Activities ◽  
Large Earthquakes

Abstract. Using IAP (plasma analyzer) and ISL (Langmuir probe) experiments onboard DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite and GPS (Global Positioning System) measurements, we have statistically analyzed the variations of the electron and ion densities to search for disturbances in the vicinity of four large earthquakes prior to events. The indices Dst and Kp were used to distinguish pre-earthquake anomalies from the other anomalies related to the geomagnetic activities. For each studied case, a very good agreement was found between the different parameters estimated by DEMETER and GPS data in the detection of pre-seismic anomalies. Our statistics results show that the anomalous deviations prior to earthquakes have different sign from case to case, and that their amplitude depends on the magnitude of the earthquake. It has also been found that the electron density measured by the ISL experiment at night detects anomalous variations significantly before the earthquakes. The appearance of positive and negative anomalies in both of DEMETER and TEC (Total Electron Content) data during 1 to 5 days before all studied earthquakes during quiet geomagnetic conditions indicates that these anomalous behaviors are highly regarded as seismo-ionospheric precursors.

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