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Unusual Change in Critical Frequency of F<sub>2</sub> Layer during and Prior to Earthquakes


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The unusualness in the critical frequency of different layers of earth’s ionosphere is commensurate to be associated with seismic events. We present study of critical frequency of F2 layer (denoted as f0F2) during some major earthquakes in South American region. We use the semi-empirical Barbier’s theorem of air-glow and define a parameter using the critical frequency and virtual height of F2 layer and named it as ‘F Parameter’. To investigate the variation of this parameter we consider five large earthquakes in the junction of Nazca plate and South American plate having magnitude greater than M > 6.5 and study the temporal variation of F parameter during these earthquakes. The F Parameter is measured using the ionograms as recorded from the Ionosonde in Jicamarca Radio Observatory (lat. 11.95◦ S, long 76.87◦ W) in Chile which lies within the earthquake preparation zones of these five earthquakes. We examine the F Parameter with in a span of ± 15 days during earthquakes and observed significant change in the evaluated F Parameter in 12 to 3 days prior to the earthquakes. The increment is over +3σ from the normal variation. We also observe significant changes during aftershock events. The solar geomagnetic indices were found to be low which ensures that these anomaly in F Parameter are due to seismic events.
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Open Journal of Earthquake Research, 2017, 6, 191-203
ISSN Online: 2169-9631
ISSN Print: 2169-9623
10.4236/ojer.2017.64012 Oct. 19, 2017 191 Open Journal of Earthquake Research
Unusual Change in Critical Frequency of F2
Layer during and Prior to Earthquakes
Soujan Ghosh1, Sudipta Sasmal1, Subrata Kumar Midya1,2, Sandip K. Chakrabarti1,3
1Indian Centre for Space Physics, Kolkata, India
2Department of Atmospheric Sciences, Calcutta University, Kolkata, India
3S. N. Bose National Centre for Basic Sciences, Kolkata, India
The unusualness in the critical frequency of different layers of earths iono
phere is commensurate to be
associated with seismic events. We present study
of critical frequency of F2 layer (denoted as f0F2) during some major eart
quakes in South American region. We use the semi-empirical Barbier’s the
rem of air-glow and define a parameter using the critical f
requency and virtual
height of F2 layer and named it as F Parameter
. To investigate the variation
of this parameter,
we consider five large earthquakes in the junction of Nazca
plate and South American plate having magnitude greater than M > 6.5 and
y the temporal variation of F parameter during these earthquakes. The F
Parameter is measured using the ionograms as recorded from the Ionosonde
in Jicamarca Radio Observatory (lat. 11.95˚S, long 76.87˚
W) in Chile which
lies within the earthquake preparati
on zones of these five earthquakes. We
examine the F Parameter within a span of ±15 days during earthquakes and
observed significant change in the evaluated F Parameter in 12 to 3 days prior
to the earthquakes. The increment is over +3σ from the normal var
iation. We
also observe significant changes during aftershock events. The solar geoma
netic indices were found to be low which ensures that these anomalies
in F
Parameter are due to seismic events.
Earthquake Early Warning, Wave Propagation, Earthquake Interaction,
Forecasting and Prediction, Ionosphere/Atmosphere Interactions,
Electrical Properties
1. Introduction
This understanding of seismicity is a vast, complicated, anisotropic and multi
How to cite this paper:
Ghosh, S., Sasmal,
., Midya, S.K. and Chakrabarti, S.K. (2017
Unusual Change in Critical Frequency of F
Layer during and Prior to Earthquakes
Journal of Earthquake Research
, 191-203.
June 15, 2017
October 16, 2017
October 19, 2017
Copyright © 201
7 by authors and
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY
Open Access
S. Ghosh et al.
10.4236/ojer.2017.64012 192 Open
Journal of Earthquake Research
parametric problem. Predictions of earthquakes from perceived precursory phe-
nomena with accurate specification of time, location and magnitude of a future
earthquake with sufficient precision is therefore not very easy. It is well recognized
that electromagnetic wave propagation technique through earth-ionosphere wa-
veguide could be an important tool to predict occurrences of seismic hazards.
The mechanism of seismicity can create a significant thermal, mechanical and
electrical perturbation in ionospheric layers through the so-called Lithos-
phere-Atmosphere-Ionosphere Coupling (LAIC). Thus any physical or chemical
changes resulting from such a coupling can be used as a precursory tool for
seismic hazards.
Ionosphere is divided in mainly three distinct layers, namely, D, E and F. F is
also divided in two sub layers, namely, F1 and F2. The behavior of F2 layer is de-
scribed in terms of the extent of its departure from that of a hypothetical Chap-
man layer. The departure can be termed as an “anomaly”. Geographical anoma-
ly, Diurnal anomaly, Seasonal anomaly, winter anomaly are some of such ano-
malies observed usually in the experimental measurement of Critical frequency
of F2 layer. The Critical frequency is the highest frequency which could be re-
flected from ionosphere. Above this frequency, the radio wave penetrates into
the upper ionosphere. The critical frequency of F2 layer is denoted by f0F2. When
a radio wave is reflected from a perfect reflector, it is likely to be reflected from a
point. But in reality the signal is continuously bent or refracted as it travels
through ionosphere, since the reflection and penetration both occurs simulta-
neously till a height is reached where the residual ray is totally reflected. Howev-
er, though the path is bent gradually, one can conceive that the incident and re-
flected rays, when extrapolated, meet at a point. This height could be called the
virtual reflection height. The virtual height of an ionized atmospheric layer is
measured by the time interval between the transmission of a radio signal and the
receipt of the return of its echo.
The existence of a phenomenon called “airglow” was probably discovered be-
fore 1800. Yntema [1] was the first person to photometrically establish the phe-
nomenon of airglow which he termed as Earthlight. Following a suggestion of
Otto Struve, Elvey [2] introduced the name airglow for the first time. From the
basic physics of airglow, related chemical kinetics and excitation mechanism and
above all, the ionospheric physics and chemistry, it is obvious that there exists a
direct relationship, either of complex or of straightforward nature between io-
nospheric parameters and airglow emissions. The well-known Barbier formula
establishes a direct relationship between the airglow intensity and the critical
frequency of the F2 layer. The variable part of this formula deals with the critical
frequency and the virtual reflection height of F layer. The airglow intensity vari-
ation depends on the charge densities and type of ions which recombines to emit
the radiation. As a whole, the critical frequency is associated with the charge
density profile of the ionospheric layers. So can be used as a tool to study the va-
riabilities of the charge density profiles. LAIC mechanism predicts anomalous
changes of charge density profile before seismic events.
S. Ghosh et al.
10.4236/ojer.2017.64012 193 Open Journal of Earthquake Research
Ionospheric disturbance associated with seismic activities has been largely
studied since the Great Alaska Earthquake in March 27, 1964 [3]-[30]. Correla-
tions of seismicity with anomaly in F-layer were achieved using different me-
thodologies from spectral analysis [31], satellite observation [32], equatorial io-
nization anomaly [33], etc. The first publications deal with ionospheric charac-
teristics variations as seismic precursors were Antselevich [34] study of the vari-
ations of f0E parameter before the Tashkent earthquake 1966. The peak electron
density in the F2 layer appears to be one of the most sensitive parameters con-
nected to seismic activity. Spatial and Temporal variation of electron concentra-
tion based on topside ionosonde data during seismic events was done by Puli-
et al.
[35]. Several studies were carried out regarding the f0F2 variation by
Gaivoronskaya & Zelenova [36]; Dupuev & Zelenova [37]; Chuo
et al.
[38]; Pu-
et al.
[39] [40]; Liu
et al.
[41]; Silina
et al.
[42]; Pulinets & Legen’ka [43];
et al.
[44]; Pulinets & Boyarchuk [16]; Hobara & Parrot [45]; Liperovskaya
et al.
In this paper, we consider five different earthquakes from South American re-
gion near Peru and Chile. We compute a variable parameter from Barbier theo-
rem using the (
2) and virtual height profile and study this parameter for a du-
ration of ±15 days around those five earthquakes. The plan of the paper is as
following: in the next Section, we explain the methodology and data analysis; in
Section 3, we present our results; and in Section 4, we draw our conclusion.
2. Data and Methodologies
In our entire analysis, we gathered the Ionosonde data from Jicamarca station
from In Figure 1, we present schematic diagram of radio
wave propagation technique to indicate the reflection height and critical fre-
Figure 1. Schematic diagram of radio wave propagation technique through earth-ionosphere
waveguide depicting the concept of critical frequency and virtual reflection height.
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We found the all the chosen earthquakes are near the junction of two tectonic
plates, the Nazca plate to the West and the South American plate to the East.
The South American Plate is in motion, moving westward away from the Mid-
Atlantic Ridge. The eastward-moving and denser Nazca Plate is sub-ducting
under the western edge of the South American Plate along the Pacific coast of
the continent at a rate of 77 mm per year. Subduction zones such as the South
America arc are geologically complex and generate numerous earthquakes from
a variety of tectonic processes that cause deformation of the western edge of
South America. The Ionosonde observatory near this place is the Jicamarca Ra-
dio Observatory (JRO) (latitude 11.95˚ South, longitude 76.87˚ West). The alti-
tude of JRO is about 520 meters above the sea level. The location of the Jicamar-
ca observatory (blue square) and the 5 earthquakes (>6.5) in the South American
region (red circle) are shown in Figure 2.
We also calculate the radius of earthquake preparation zone for these chosen
earthquakes using Dobrovolsky formula [47]
10 km
is the radius of the earthquake preparation zone and
is the Richter
magnitude of the earthquake. We found that the distance of Jicamarca Radio
Observatory from the epicenter of 5 earthquake lies within the preparation zone.
The detail information of the earthquakes is given in Table 1.
Figure 2. The location of Jicamarca Ionosonde observatory (blue square)
and epicenters of five earthquakes (red circles) under consideration.
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Table 1. Earthquake details.
Date Magnitude Lat (S) Long (W)
Radius of
zone (km)
Distance from
Jicamarca Radio
Observatory (km)
15/08/2007 8 13.32 76.51 2754.2287 157.3
23/06/2001 8.4 16.26 73.64 4092.6065 592.4
01/04/2014 8.2 19.64 70.81 3357.3761 1073
25/09/2005 7.5 5.67 76.41 1678.8040 700.1
28/10/2011 6.9 14.52 76.01 926.8298 300.5
In Figure 3, we present a typical ionogram as obtained from the Jicamarca
station. The ionogram is a six-dimensional display, with sounding frequency as
the abscissa, virtual reflection height (simple conversion of time delay to range
assuming propagation at 3 × 108 m/sec) as the ordinate, signal amplitude as the
dot size, and echo status (Polarization, Doppler shift, and angle of arrival)
mapped into 12 available distinct colors. The wave polarizations are shown as
two different color groups. Firstly, the green scale, “neutral” colors showing ex-
traordinary polarization and the red scale, “demanding attention” colors show-
ing ordinary polarization. The angle of arrival is shown by different colors (using
the “warm” scale for South and the “cold” scale for North) and the Doppler shift
is indicated by the color shades. The left side of Figure shows a table of ionos-
pheric characteristics scaled automatically by the ARTIST software [48].
The airglow intensity variation can be can mathematically represented as,
[ ]
( )
02 0
Airglow intensity expfF z z H
∝ −−
Barbier [49] [50] was the first to establish a semi empirical formula for OI
6300 Å airglow emission which is given by,
is the scale height in terms of oxygen and was assumed by Barbier
himself to be equal to 80 km. We only consider the variable part of this semi
empirical formula and modified this equation to
( )
6300 0 2
expQ f F hF H
We name the variable quantity
expf F hF H
calculate this for all the five earthquakes to check possible correlations.
3. Result
We compute the
value for all the earthquakes using the
2 from the iono-
grams. Figure 4 shows the variation of
2 for a duration of 15 days from 18
September to 2 October 2001. The black curves are the actual values of
2 rec-
orded as an interval of 30 minutes. So for each single day, there are 48 data
points. The red curves are the average variation of
2 for the same time period
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Figure 3. A typical ionogram as observed from Jicamarca Lowell Digisonde instrument
Figure 4. The variation of f0F2 as a function of day number around the earthquake day on
25 September, 2005. The black curves are the actual f0F2 variations where the red curves
are the average value of f0F2 when there was no earthquake. There was strong earthquake
on 25 September, 2005. There is an enhancement of f0F2, four days before the earthquake.
The peak after the earthquake day is due to the major aftershocks after the main quake.
for which there were no significant seismic event. Therefore the red curve is a
basic calibration of the regular variation of
2 in a seismically quiet condition.
An earthquake of Richter scale magnitude (
= 7.5) occurred on 25 September,
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2005. It is clear from the above Figure that the value of
2 increases unusually
four days before the earthquake. There is a similar enhancement of
2 just after
the earthquake. After the main shock there were a series of aftershocks up to 3 to
4 days with average magnitude more than 5.5. The origin of the second peak is
possibly due to these aftershocks.
We computed F parameter for all the earthquakes under consideration using
the formula mentioned above. Figure 5 shows variation of F parameter as a
function of time in days for a span of 21 (10 days before and after) days around
the earthquake. The thick curve is the average value of F parameter. We calculate
the standard deviation from the mean value and plotted the ±σ, ±2σ and ±3σ
with the thick dashed, dotted-dashed and dotted curves respectively with the av-
erage value.
Figure 5 shows an enhancement of the F parameter six days before the earth-
quake. The zero of the X-axis represents the day of the earthquake. It is clear that
the F parameter increases anomalously with an order of more than 5σ from the
average value. The variation of F parameter does not follow the actual f0F2 varia-
tion as presented in Figure 4. There is no secondary maximum after the earth-
quake day. So the entire effect is pre-seismic.
In Figure 6, we present variation of F parameter for the rest of the four
earthquakes in a single grid. The for graphs represents the earthquake as (a)
01/04/2014; (b) 15/08/2007; (c) 23/06/2001 and (d) 28/10/2011. We follow the
same convention for calculating the σ and put the different σ level envelop with
the same line style we use in Figure 5. The zero represents the earthquake day
marked as E.
Figure 5. The variation of F parameter as a function of day number for ±10 days around
the earthquake day on 25 September, 2005. The thick solid curve is the average value of
the F parameter. The dashed, dotted-dashed and dotted curves are for ±σ, ±2σ and ±3σ
level respectively added with the average curve. E is the day of the earthquake. F parame-
ter shows an enhancement before the earthquake.
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Figure 6. The variation of f 0 F 2 as a function of day number for the four earthquakes (a)
01/04/2014; (b) 15/08/2007; (c) 23/06/2001 and (d) 28/10/2011. The dashed, dotted-
dashed and dotted curves are for ±σ, ±2σ and ±3σ level respectively added with the aver-
age curve. E is the day of the earthquake.
Figure 6 shows a similar enhancement of F parameter for all the cases. For
(a), (b) and (d), the F parameter suffers from an enhancement on 3 to 9 days
before the earthquake. For the case of 28 October, 2011 (d), the maximum is
quite sharp and reaches more than 7σ level. For (a) 1 April, 2014 and (b) 15 Au-
gust, 2007, the enhancement is not so sharp but crosses 3σ and 2σ level respec-
tively. For the case of (c) 23 June, 2001, the behavior of F parameter is still ano-
malous but rather different. The F value becomes minimum on the day of the
earthquake. Before the earthquake the F value is quite higher than that for the
earthquake day but the values just cross the σ level. The value has a pre-seismic
maxima on 11 days prior to the maxima but have significant secondary maxima
on 2 to 5 days after the earthquake day. There are two possible reasons behind
this post-seismic maxima. First, there are a series of aftershocks occurred for this
earthquake. Secondly, there was another strong earthquake with Magnitude M =
7.6 occurring on 7 July, 2001. The secondary peak can be due to pre-seismic ef-
fects of the second quake as the second main shock occurs within the next 14
days. So we believe the post-seismic shocks are due to the combined effects of
these two factors. To check the solar geomagnetic condition during the earth-
quake and its associated days we plot the geomagnetic k p index for ±7 days
around the earthquake day for all the 5 earthquakes. Figure 7 shows variation of
kp index for a duration of 15 days.
It is clear from Figure 7 that during all the earthquakes and their surrounding
days, the value k p index ranges between 0 to 4.29 which implies geomagnetically
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Figure 7. Variation of geomagnetic k p index on and around five earthquakes [(a) 25/09/2005; (b) 01/04/2014; (c) 15/08/2007; (d)
23/06/2001 and (e) 28/10/2011]. For all the earthquakes, kp index is below 5.
quiet condition (kp < 5). So for the signal has no perturbation due to solar geo-
magnetic activities and the anomaly in the signal is due to the seismic events.
4. Conclusion
The LAIC mechanism relates properties of apparently distant and distinct com-
ponents of Earth system science ranging from lithosphere, lower ionospheric
D-layer to upper F2 layer. Starting from the tropospheric thermal anomalies,
lower ionospheric electron density variation to upper ionospheric critical fre-
quency modulation, LAIC takes into account a wide range of geochemical and
geo-physical phenomena which could be affected simultaneously. In this paper,
S. Ghosh et al.
10.4236/ojer.2017.64012 200 Open
Journal of Earthquake Research
we focused our study on the ionospheric F2 layer where we observe the critical
frequency variation for a span of three weeks during some strong seismic events
in South America region. We compute a parameter (F) which contains the criti-
cal frequency of F2 layer (f0F2) and the virtual reflection height (h') from the his-
toric Barbier’s airglow equation and study the behavior of this parameter during
those earthquake days. We observe significant increase of this parameter on
three to nine days prior to those seismic events. We observe the effects of the af-
tershocks in the direct observation of both f0F2 and F parameter. We also pre-
sented the geomagnetic kp indices for all the five earthquakes and found low
geomagnetic condition during all the earthquakes, suggesting our assumption of
LAIC mechanism. As yet, we have no clear idea of how and why exactly the li-
thospheric changes percolate into ionospheric changes. However, our study
proves that such changes do occur. Study of physical mechanisms behind the
LAIC mechanism and implementing acquired knowledge for future earthquake
prediction, regular monitoring of such parameters is absolutely essential to
achieve our goal. At the same time, we need to increase number of receiving sta-
tions so as to compare the anomalies from different points in order to locate the
epicenter with accuracy.
The authors thank to Lowell Digisonde International, Prof. Bodo W. Reinisch
and United States Geological Survey (USGS) for providing the ionogram and
earthquake data respectively. S. Ghosh and S. Sasmal acknowledge Ministry of
Earth Sciences (MoES) for financial support.
[1] Yntema, L. (1909) On the Brightness of the Sky and Total Amount of Starlight: An
Experimental Study. Publications of the Kapteyn Astronomical Laboratory, Gro-
ningen, 22, 62.
[2] Elvey, C.T. (1950) Note on the Spectrum of the Airglow in the Red Region.
physical Journal
, 111, 432-433.
[3] Davis, K. and Barker, D. (1965) Ionospheric Effects Observed around the Time of
the Alaska Earthquake of March 1964.
Journal of Geophysical Research
, 70,
[4] Hayakawa, M. and Fujinawa, Y. (1994) Electromagnetic Phenomena Related to
Earthquake Prediction. Terra Scientific Publication Company, Tokyo.
[5] Calais, E. and Minster, J.B. (1995) GPS detection of Ionospheric Perturbations Fol-
lowing the January 17, 1994, Northridge Earthquake.
Geophysical Research Letters
22, 1045-1048.
[6] Chmyrev, V.M., Isaev, N.V., Serebryakova, O.N., Sorokin, V.M. and Sobolev, Y.P.
(1997) Small-Scale Plasma Inhomogeneities and Correlated ELF Emissions in the
Ionosphere over an Earthquake Region.
Journal of Atmospheric and Solar-Terrestrial
, 59, 967-974.
[7] Liperovsky, V.A., Pokhotelov, O.A., Liperovskaya, E.V., Parrot, M., Meister, C.V.
and Alimov, O.A. (2000) Modification of Sporadic E-Layers Caused by Seismic Ac-
Surveys in Geophysics
, 21, 449-486.
S. Ghosh et al.
10.4236/ojer.2017.64012 201 Open Journal of Earthquake Research
[8] Liu, J.Y., Chen, Y.I., Chuo, Y.J. and Tsai, H.F. (2001) Variations of Ionospheric To-
tal Content during the Chi-Chi Earthquake.
Geophysical Research Letters
, 28,
[9] Liu, J.Y., Chuo, Y.J., Pulinets, S.A., Tsai, H.F. and Zeng, X. (2002) A Study on the
TEC Perturbations Prior to the Rei-Li, Chi-Chi and Chia-Yi Earthquakes. In:
Hayakawa, M. and Molchanov, O.A., Eds.,
phere-Atmosphere-Ionosphere Coupling
, TERRAPUB, Tokyo, 297-301.
[10] Liu, J.Y., Chuo, Y.J., Shan, S.J., Tsai, Y.B., Pulinets, S.A. and Yu, S.B. (2004)
Pre-Earthquake Anomalies Registered by Continuous GPS TEC Measurements.
Annales Geophysicae
, 22, 1585-1593.
[11] Liu, J.A., Tasi, Y.B., Chen, S.W., Lee, C.P., Chen, Y.C., Yen, H.Y., Chang, W.Y. and
Liu, C. (2006) Giant Ionospheric Disturbances Excited by the M9.3 Sumatra Earth-
quake of 26 December 2004.
Geophysical Research Letters
, 33, L02103.
[12] Gaivoronskaya, T.V. and Pulinets, S.A. (2002) Analysis of F2-Layer Variability in
the Areas of Seismic Activity.
, 2, 20.
[13] Plotkin, V.V. (2003) GPS Detection of Ionospheric Perturbation before the 13 Feb-
ruary 2001, El Salvador Earthquake.
Natural Hazards and Earth System Sciences
, 3,
[14] Afraimovich, E.L., Astafieva, E.I. and Voyeikov, S.V. (2004) Isolated Ionospheric
Disturbances as Deduced from Global GPS Network.
Annales Geophysicae
, 22,
[15] Trigunait, A., Parrot, M., Pulinets, S. and Li, F. (2004) Variations of the Ionospheric
Electron Density during the Bhuj Seismic Event.
Annales Geophysicae
, 22,
[16] Pulinets, S.A. and Boyarchuk, K.A. (2004) Ionospheric Precursors of Earthquakes.
Springer, Berlin, 315.
[17] Pulinets, S.A., Boyarchuk, K.A., Hegai, V.V. and Karelin, A.V. (2002) Conception
and Model of Seismo-Ionosphere-Magnetosphere Coupling. In: Hayakawa, M. and
Molchanov, O.A., Eds.,
Atmosphere Ionos-
phere Coupling
, TERRAPUB, Tokyo, 353-361.
[18] Pulinets, S.A., Ouzounov, D., Ciraolo, L., Singh, R., Cervone, G., Leyva, A., Duna-
jecka, M., Karelin, A.V., Boyarchuk, K.A. and Kotsarenko, A. (2006) Thermal, At-
mospheric and Ionospheric Anomalies around the Time of the Colima M 7.8
Earthquake of 21 January 2003.
Annales Geophysicae
, 24, 835-849.
[19] Larkina, V.I., Migulin, V.V., Nalivaiko, A.V., Gershenzon, N.I., Gokhberg, M.B.,
Liperovsky, V.A. and Shalimov, S.L. (1983) Observation of VLF Emissions, Related
with Seismic Activity, on the Intercosmos-19 Satellite.
Geomagnetism and Aero-
, 23, 684-687.
[20] Zakharenkova, I.E., Shagimuratov, I.I., Krankowski, A. and Lagovsky, A.F. (2007)
Precursor Phenomena Observation in the Electron Content Measurements before
Great Hokkaido Earthquake of September 25, 2003, (M = 8.3).
Studia Geophysica et
, 51, 267-278.
[21] Zakharenkova, I.E., Shagimuratov, I.I. and Krankowski, A. (2007) Features of the
Ionosphere Behavior before the Kythira 2006 Earthquake.
Acta Geophysica
, 55,
S. Ghosh et al.
10.4236/ojer.2017.64012 202 Open
Journal of Earthquake Research
[22] Zakharenkova, I.E., Shagimuratov, I.I., Tepenitzina, N.Y. and Krankowski, A.
(2008) Anomalous Modification of the Ionospheric Total Electron Content Prior to
the 26 September 2005 Peru Earthquake.
Journal of Atmospheric and So-
Terrestrial Physics
, 70, 1919-1928.
[23] Chakrabarti, S., Sasmal, S., Saha, M., Khan, R., Bhoumik, D. and Chakrabarti, S.K.
(2007) Unusual Behavior of D-Region Ionization Time at 18.2 kHz during Seismi-
cally Active Days.
Indian Journal of Physics
, 81, 531-538.
[24] Chakrabarti, S.K., Saha, M., Khan, R., Mandal, S., Acharyya, K. and Saha, R. (2005)
Possible Detection of Ionospheric Disturbances during the Sumatra-Andaman Isl-
ands Earthquakes of December, 2004.
Indian Journal of Radio & Space Physics
, 34,
[25] Chakrabarti, S.K., Sasmal, S. and Chakrabarti, S. (2010) Ionospheric Anomaly Due
to Seismic Activities Part 2: Evidence from D-Layer Preparation and Disappearance
Natural Hazards and Earth System Sciences
, 10, 1751-1757.
[26] Sasmal, S. and Chakrabarti, S.K. (2009) Ionospheric Anomaly Due to Seismic Activ-
ities I: Calibration of the VLF signal of VTX 18.2 kHz Station from Kolkata and
Deviation during Seismic Events.
Natural Hazards and Earth System Sciences
, 9,
[27] Sasmal, S., Chakrabarti, S.K. and Ray, S. (2014) Unusual Behavior of Very Low
Frequency Signal during the Earthquake at Honshu/Japan on 11 March, 2011.
dian Journal of Physics
, 88, 1013-1019.
[28] Ray, S., Chakrabarti, S.K., Mondal, S. and Sasmal, S. (2011) Correlation between
Night Time VLF Amplitude Fluctuations and Effective Magnitudes of Earthquakes
in Indian Sub-Continent.
Natural Hazards and Earth System Sciences
, 11,
[29] Ray, S., Chakrabarti, S.K. and Sasmal, S. (2012) Precursory Effects in the Night
Time VLF Signal Amplitude for the 18th Jan. 2011 Pakistan Earthquake.
Journal of Physics
, 86, 85-88.
[30] Molchanov, O.A., Hayakawa, M., Ondoh, T. and Kawai, E. (1998) Precursory Ef-
fects in the Subionospheric VLF Signals for the Kobe Earthquake.
Physics of the
Earth and Planetary Interiors
, 105, 239-248.
[31] Zelenova, T.I. and Legenka, A.I. (1989) Ionospheric Effects Related to the Moneron
Earthquake of September 5(6) 1971, Izvestiya.
Earth Physics
, 25, 848-853.
[32] Pulinets, S.A. (1998) Strong Earthquakes Prediction Possibility with the Help of
Topside Sounding from Satellites.
Advances in Space Research
, 21, 455-458.
[33] Ryu, K., Lee, E., Parrot, M. and Oyama, K.I. (2014) Multisatellite Observations of
Enhancement of Equatorial Ionization Anomaly around Northern Sumatra Earth-
quake of March 2005.
Journal of Geophysical Research
, 119, 4767-4785.
[34] Antselevich, M.G. (1971) The Influence of Tashkent Earthquake on the Earth’s
Magnetic Field and the Ionosphere. In:
Tashkent Earthquake
1966, FAN
Publ., 187-188.
[35] Pulinets, S.A., Legenka, A.D., Karpachev, A.T., Kochenova, N.A., Fligel, M.D., Mi-
gulin, V.V. and Oraevsky, V.N. (1991) The Earthquakes Prediction Possibility on
the Base of Topside Sounding Data.
, 34, 25.
[36] Gaivoronskaya, T.V. and Zelenova, T.I. (1991) The Effect of Seismic Activity on F2
Layer Critical Frequencies.
Journal of Atmospheric and Terrestrial Physics
, 53,
S. Ghosh et al.
10.4236/ojer.2017.64012 203 Open Journal of Earthquake Research
[37] Depuev, V. and Zelenova, T. (1996) Electron Density Profile Changes in a
Pre-Earthquake Period.
Advances in Space Research
, 18, 115-118.
[38] Chuo, Y.J., Chen, Y.I., Liu, J.Y. and Pulinets, S.A. (2001) Ionospheric f0F2 Variations
Prior to Strong Earthquakes in Taiwan Area.
Advances in Space Research
, 27,
[39] Pulinets, S.A., Kim, V.P., Hegai, V.V., Depuev, V.K. and Radicella, S.M. (1998) Un-
usual Longitude Modification of the Nighttime Midlatitude F2 Region Ionosphere
in July 1980 over the Array of Tectonic Faults in the Andes Area: Observations and
Geophysical Research Letters
, 25, 4143-4136.
[40] Pulinets, S.A., Boyarchuk, K.A., Lomonosov, A.M., Khegai, V.V. and Liu, J.Y.
(2002) Ionospheric Precursors to Earthquakes: A Preliminary Analysis of the f0F2
Critical Frequencies at Chung-Li Ground-Based Station for Vertical Sounding of
the Ionosphere (Taiwan Island).
Geomagnetism and Aeronomy
, 42, 508-513.
[41] Liu, J.Y., Chen, Y.I., Pulinets, S.A., Tsai, Y.B. and Chuo, Y.J. (2000) Seismo Ionos-
pheric Signatures Prior to M ≥ 6.0 Taiwan Earthquakes.
Geophysical Research Let-
, 27, 3113-3116.
[42] Silina, A.S., Liperovskaya, E.V., Liperovsky, V.A. and Meister, C.V. (2001) Ionos-
pheric Phenomena before Strong Earthquakes.
Natural Hazards
, 1, 113-118.
[43] Pulinets, S.A. and Legen’ka, A.D. (2003) Spatial-Temporal Characteristics of the
Large Scale Disturbances of Electron Concentration Observed in the F-Region of
the Ionosphere before Strong Earthquakes.
Kosmicheskie issledovaniya
), 41, 1-10.
[44] Rios, V.H., Kim, V.P. and Hegai, V.V. (2004) Abnormal Perturbations in the F2 Re-
gion Ionosphere Observed Prior to the Great San Juan Earthquake of 23 November
Advances in Space Research
, 33, 323-327.
[45] Hobara, Y. and Parrot, M. (2005) Ionospheric Perturbations Linked to a Very Po-
werful Seismic Event.
Journal of Atmospheric and Solar
Terrestrial Physics
, 67,
[46] Liperovskaya, E.V., Meister, C.V., Pokhotelov, O.A., Parrot, M., Bogdanov, V.V.
and Vasileva, N.E. (2006) On Es-Spread Effects in the Ionosphere Connected to
Natural Hazards and Earth System Science
, 6, 741-744.
[47] Dobrovolsky, I.R., Zubkov, S.I. and Myachkin, V.I. (1979) Estimation of the Size of
Earthquake Preparation Zones.
, 117, 1025-1044.
[48] Reinisch, B.W. and Galkin, I.A. (2011) Global Ionospheric Radio Observatory
and Space
, 63, 377-381.
[49] Barbier, D. (1957) La lumiere du ciel nocturne en ete a Taamanrasset. [The Light of
the Night Sky in Summer in Taamanrasset.]
Comptes Rendus de l
Académie des
, 245, 1559-1561.
[50] Barbier, D. (1959) Recherches sur la raie 6300 de la luminescence atmospherique
nocturne. [Research on the 6300 Line of Atmospheric Luminescence Nocturne.]
Annals of Geophysics
, 15, 179-217.
... The possible earthquakeionospheric correlation is reported for the first time by Bolt (1964) after the great ''Alaskan earthquake", using the ionosonde method. Since then, several methods and articles have been published to confirm the seismicionosphere relationship Davis and Baker, 1965;Yuen et al., 1968;Gokhberg et al., 1989;Kundu et al., 2022;Chakraborty et al., 2019;Ghosh et al., 2017;Ghosh et al., 2022). ...
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Lower ionospheric perturbation during earthquake activity is well recognized by the anomalous behavior of Very Low or Low Frequency (VLF/LF) radio signal. In this study, we present the sub-ionospheric VLF signal modulation during the Samos earthquake that took place on October 30, 2020 (M = 6.9). We use the conventional terminator time method to check the seismogenic impression in the VLF signal during the local sunrise and sunset times. VLF signals from two transmitters ISR (Israel) and TBB (Turkey) are used for this analysis and those are recorded in a receiving station UWA in Greece. Both signals show a strong shift in the sunrise and sunset termi-nator times. The signal profiles are numerically simulated using the Long Wavelength Propagation Capability (LWPC) program by incorporating Wait's two-component ionospheric parameters (b and h 0). The simulation gives highly satisfactory outcomes. The outputs of LWPC are used to compute the electron density profile of the lower ionosphere. It is found that the electron density gets significantly modulated during the maximum shift in the terminator times. The electron density is found to have both increased and decreased from its normal value before the earthquake. The VLF path dependency is strongly observed in the change in the electron density profile. For ISR-UWA, nighttime reflection height has been computed using the modal conversion technique, and it is found to be similar to the LWPC outcomes. The overall condition was geomagnetically quiet, and the results have no contamination due to solar-terrestrial interaction.
... Equation (1) derived by Barbier was later carefully verified (Carman and Kilfoyle, 1963) for GVISS TOWNSVILLE in the Southern Hemisphere (19.25° S, 146.75° E). Ghosh et al. (2017) defined the combined parameter F ≡ (foF2) 2 exp{h'F/H} based on the variable part of Barbier's formula for the analysis of pre-and postseismic activity from ionospheric data and found a significant increase few days before several earthquakes. Note, first, that the mean of that parameter was determined over 24 h, and, second, the sign of the exponent is "+," in contrast to Barbier's formula. ...
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A new relative parameter (δ Barbier) is proposed for the analysis of ionospheric disturbances and the search for ionospheric precursors of earthquakes. The parameter is derived on the basis of the semiempirical Barbier's formula, in which directly and simultaneously measured ionospheric parameters are used: the critical frequency of F2 layer of the ionosphere foF2 and the virtual minimum height of F region h'F. The time prior to a 6.2-magnitude earthquake that occurred in the vicinity of the ground-based station of vertical ionospheric sounding MAUI (Hawaii) on June 26, 1989, is considered as an example of the use of this parameter and its interpretation. We show that δ Barbier ≤ 0 during dark hours, from 2000 to 0400 local time, against the geomagnetically quiet background (Kp ≤ 2 +) on June 25, 1989, i.e., the day before the earthquake. This behavior is interpreted as a decrease (as compared to the median) in the glow intensity of the atomic oxygen O(1 D) emission in the red line (630 nm) estimated from ionospheric data, which is associated with the dissociative recombination of ions at altitude of the F region during this time. The studied effect can be seismogenic and can serve an ionospheric precursor of an earthquake.
... LAIC is proposed to be functional through three major channels: (a) the chemical, (b) the acoustic, and (c) the electromagnetic [3]. There are a wide variety of processes involving electromagnetic disturbances, starting from disruption in the very low frequency (VLF)/low frequency radio signals and ultralow frequency (ULF)/extreme low frequency (ELF) [4][5][6][7][8][9][10][11][12], changes in plasma density in higher ionospheric altitudes [13][14][15], irregularities in total electron content (TEC) [16][17][18][19][20][21][22] etc. The primary acting agent of the acoustic channel is atmospheric gravity wave (AGW) excitation, which may occur as an outcome of atmospheric oscillation in stratospheric heights above the epicenter of a similar earthquake, swaying upward, and disrupting upper atmospheric altitudes. ...
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Atmospheric disturbances caused by seismic activity are a complex phenomenon. The Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) (LAIC) mechanism gives a detailed idea to understand these processes to study the possible impacts of a forthcoming earthquake. The atmospheric gravity wave (AGW) is one of the most accurate parameters for explaining such LAIC process, where seismogenic disturbances can be explained in terms of atmospheric waves caused by temperature changes. The key goal of this work is to study the perturbation in the potential energy associated with stratospheric AGW prior to many large earthquakes. We select seven large earthquakes having Richter scale magnitudes greater than seven (M>7.0) in Japan (Tohoku and Kumamoto), Mexico (Chiapas), Nepal, and the Indian Ocean region, to study the intensification of AGW using the atmospheric temperature profile as recorded from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite. We observe a significant enhancement in the potential energy of the AGW ranging from 2 to 22 days prior to different earthquakes. We examine the conditions of geomagnetic disturbances, typhoons, and thunderstorms during our study and eliminate the possible contamination due to these events.
... Many ground-and space-based instruments are used to detect these disturbances [1,24,25]. The anomalies are observed using ground-based observations with the Very-Low-Frequency (VLF)/Low frequency (LF) radio wave, Critical frequency of F2 layers ( f 0F 2 ), Total Electron Content (TEC), Ultra Low-Frequency (ULF) emissions, etc. [26][27][28][29][30][31][32][33][34]. In parallel, a lot of space-based techniques have been used to investigate the LAIC mechanisms. ...
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Citation: Sasmal, S.; Chowdhury, S.; Kundu, S.; Politis, D.Z.; Potirakis, S.M.; Balasis, G.; Hayakawa, M.; Chakrabarti, S.K. Pre-Seismic Irregularities during the 2020 Samos (Greece) Earthquake (M = 6.9) as Investigated from Multi-Parameter Approach by Ground and Space-Based Techniques. Atmosphere 2021, 12, 1059. https://doi.
... The ionospheric plasma frequency (or electron density) was recorded by a local ionosonde; it was found that the critical frequency of F2 peak showed an anomaly few days prior to most of the M ≥ 6.0 earthquakes in Taiwan between 1994-1999 [19]. The "F parameter" calculated from Barbier equation of airglow emission significantly changes 12 to 3 days prior to five major earthquakes in Najca and South American plate junction [20]. Discussion of seismoionospheric phenomena observed through TEC anomaly can be found in many works [21][22][23][24][25]. LAIC (Lithosphere Atmosphere Ionosphere Coupling) model reported that seismicity can create significant thermal, mechanical, and electrical perturbations in ionospheric layers through LAI coupling [26,27]. ...
The intensity variation of 557.7 nm oxygen green line and 630.0 nm oxygen red line at Kiso observatory, Tokyo, and variations in critical frequency of the ionospheric F2 layer (foF2) and semi transparency coefficient related to the E layer before earthquakes with magnitude ≥ 5 are considered for 1979 to 1990. The intensity of both the lines increases within six days before earthquakes; foF2 and semi transparency coefficient abnormally increase before enhancement of airglow. The superposed epoch analysis of each variable is done for further confirmation. Some physical processes in atmosphere-ionosphere in pre-seismic days enhance the concentration of electron and neutral molecules in the ionospheric F and E regions. These events influence the dissociative recombination processes related to oxygen emission, and so the intensity of two line emissions show some special type of variations during earthquake events.
Conference Paper
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In this paper we present the unusual behavior of critical frequency of ionospheric F2 layer during several large earthquakes in the western coast of South America from 2001 to 2005. We define a new parameter from Barbier's theorem and named it as Ionospheric Parameter (F). We consider five large earthquakes having Richter scale magnitudes greater than six (M > 6.5) and study temporal variation of this newly defined ionospheric parameter (F). Critical frequency and Virtual height are measured by ground based Ionosonde station at Jicamarca (lat. 11.95 S, long 76.87 W) in Chile which lies at a distance within a radius of 1000 km from the epicenter of the quakes under consideration. The critical frequency of F2 layer (denoted as f0F2) and virtual height of F layer (h_F) are used to examine the ionospheric variation during earthquake at a span of ±15 days. We observe significant increase in the evaluated F parameter in 12 to 3 days prior to the earthquakes. The increment is over +-3 from the normal variation. The f0F2 values also revealed significant anomaly is considered as a supporting evidence for our observed correlation. We also check geomagnetic indices in order to establish that these anomalies are indeed due to seismic events only.
Earthquake is a very complex and multiparametric process. Earthquake occurrence is related to the earth’s tectonic structure and crustal dynamics. The net energy released during an earthquake causes some irregularities at the different layers of the atmosphere. In this review work, we choose a complete different approach to discuss about the seismic mechanism and associated significant thermal, mechanical and electrical perturbation in ionospheric and tropospheric layers through the so-called Lithosphere-Atmosphere-Ionosphere Coupling (LAIC). The thermal, VLF, and critical frequency anomalies are analyzed as the tools respectively to probe the tropospheric, lower ionospheric and upper ionospheric perturbations. Respective data collected from different satellites and ground based receivers are analysed and the results are presented here. © Springer International Publishing AG, part of Springer Nature 2018.
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We have been monitoring the VTX3 station at Vijyanarayanam which transmits Very Low Frequency (VLF) signal at 18.2 kHz using the Stanford University made receiver stationed at our Centre. We observe significant anomalies of the formation time of the D-region of the ionosphere at the Sunrise during the seismically active days. We have analyzed this data for over five months (1st November 2006 to 28th April 2007) and have noticed that during or before the earthquakes which took place in the neighboring region, the formation time is very anomalous in comparison to the normal days and therefore this may be used as a precursor to the earthquakes. We suspect that this abnormal behavior is due to the Lithosphere-Ionosphere coupling. To our knowledge this anomalous behaviour has never been reported before.
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We present evidence of unusual Very Low Frequency (VLF) signal amplitude variation during the devastating earthquake of magnitude 9.0 which occurred at Honshu, in Japan on 11 March, 2011. We use the SoftPAL very low frequency receiver placed at Ionospheric and Earthquake Research Centre of Indian Centre for Space Physics, located at Sitapur (Lat. 22°30′N, Long. 87°47′E). We observe significant changes in signal amplitude from JJI (Lat. 32°05′N, Long. 131°51′E) station transmitting at a frequency of 22.2 kHz prior to the earthquake. We analyze signal amplitude for almost 2 weeks to establish a possible seismo–ionospheric correlation. We observe significant shift of the sunrise terminator time up to 2 days before the earthquake and the shift is found to be maximum on the day of the earthquake. In addition, we observe unusual increase of the D-layer disappearance time during the earthquake and the value becomes maximum on the day of the earthquake. These findings generally agree with our previous findings reported elsewhere.
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Digisonde ionospheric sounders installed at 80+ locations in the world have gradually evolved their generally independent existence into a Global Ionospheric Radio Observatory (GIRO) portal. Today GIRO provides public access to 30+ million records of ionospheric measurements collected at 64 locations, of which 42 provide real-time feeds, publishing their measurement data within several minutes from their completion. GIRO databases holding ionogram and Doppler skymap records of high-frequency ionospheric soundings have registered connections from 123 organizations in 33 countries. Easy access to the global state of the ionospheric plasma distribution given in accurate and fine detail by the ionosonde measurements has inspired a number of studies of the ionospheric response to space weather events. Availability of GIRO data with minimal latency allows for the assimilation of the ionogram-derived data in real-time models such as the real-time extension planned for the International Reference Ionosphere.
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We present the results of an analysis of year-long (2007) monitoring of night time data of the VLF signal amplitude from the Indian Navy station VTX at 18.2 kHz, received by the Indian Centre for Space Physics, Kolkata. We analyzed this data to find out the correlation, if any, between night time amplitude fluctuation and seismic events. We found, analyzing individual cases (with magnitudes >5) as well as statistical analysis (of all the events with effective magnitudes greater than 3.5), that night time fluctuation of the signal amplitude has the highest probability to be beyond the 2sigma level about three days prior to seismic events. Thus, the night time fluctuation could be considered as a precursor to enhanced seismic activities.
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This paper examines variations of the greatest plasma frequency in the ionosphere, foF2, recorded by the Chung-Li ionosonde (25.0° N, 121.1° E) before M>=6.0 earthquakes during 1994-1999. The 15-day running median and the associated inter-quartile range are utilized as the reference and the upper or lower bounds to monitor the ionospheric foF2 variations for finding seismo-ionospheric signatures (precursors) of the earthquakes. It is found that precursors, in the form of the recorded foF2 falling below its associated lower bound around 1200-1700 LT, appear 1-6 days prior to these earthquakes. On September 20, 1999 UT (September 21, Taiwan local time) a large Mw=7.7 earthquake struck central Taiwan near the small town of Chi-Chi. We analyzed the foF2 and found three clear precursors 1, 3, and 4 days prior to the Chi-Chi earthquake.
The results of the continuous monitoring of ionospheric disturbances using very low frequency (VLF) radio waves during the recent Sumatran earthquake are presented. Strong and anomalous shifts in the sunset-terminator are found during 22-31 Dec. 2004. Anomalous behaviours in daytime observation are also detected. On 26 Dec. 2004, there were altogether 23 major earthquakes and aftershocks (magnitudes 5.0-9.0 on Richter scale). There were 10 such earthquakes on 27 Dec., 2 on 28 Dec., 7 on 29 Dec. and 4 on the 30 Dec. 2004. Given that there was no major earthquake on 22 December, though anomaly began on that day, it is believed that VLF monitoring could be a useful tool for earthquake predictions as well.
The VLF/LF receiving network is established in Japan (and also Kamchatka, Taiwan and Indonesia) composed of seven observing stations in Japan (Moshiri (Hokkaido), Chofu (UEC), Tateyama (Chiba), Shimizu, Kasugai (Nagoya) and Kochi). At each station we observe simultaneously several VLF/LF transmitter signals (Japanese JJI (40 kHz, Fukushima), JJI (Ebino, Kyusyu), and foreign VLF transmitters (NWC (Australia), NPM (Hawaii), NLK (USA). This Japanese VLF/LF network is used to study the ionospheric perturbations associated with earthquakes, and we present a few case studies (like Niigata Chuetsu earthquake, Sumatra earthquake) and statistical studies on the correlation between ionospheric perturbations (in the form of VLF/LF propagation anomaly) and earthquakes.
The book aims to explain the variations of near-Earth plasma observed over seismically active areas several days/hours before strong seismic shocks. It demonstrates how seismo-ionospheric coupling is part of the global electric circuit and shows that the anomalous electric field appearing in active seismic areas is the main carrier of information from the earth into the ionosphere. The discussion of physical mechanisms is based on experimental data. The results can be regarded as the basis for future applications such as short-term earthquake prediction. It proceeds to describe existing complex systems of space-born and ground-based monitoring for electromagnetic and ionospheric precursors of earthquakes, as well as those still under construction. It is an excellent text for courses and contains a wealth of information for those scientists working in the field of natural disaster reduction. © Springer-Verlag Berlin Heidelberg 2004. All rights are reserved.
Here, we report multi-satellite observations of ionospheric disturbances in relation to the occurrence of the M8.7 northern Sumatra earthquake of 28 March 2005. The DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) and CHAMP (Challenging Minisatellite Payload) satellite data were investigated to find possible precursory and post-event phenomena. It was found that EIA (Equatorial Ionization Anomaly) strength expressed in the apex height, derived from the CHAMP plasma-density profile, were intensified along the orbits whose longitudes were close to the epicenter within about a week before and after occurrence of the earthquake. Increases in electron and O+ density along the orbits close to the epicenter were also observed in the DEMETER measurements. The normalized equatorial plasma density derived from the DEMETER measurements showed intensification about a week before and after the earthquake reaching maximum the day after the shock and afterwards disappearing. In addition, similar behavior of the EIA enhancements related to the M8.0 Pisco earthquake of 15 August 2007 was observed. Surveys of space weather and geomagnetic activities excluded the possibility that these fluctuations were caused by changes in space weather or by a geomagnetic storm. Statistical analyses of the longitudinal variation revealed that the EIA was enhanced in the west of the epicenter and reduced in the east of the epicenter, and this fits the ‘increased conductivity’ model. Based on these observations, we proposed a revised view of seismo-ionospheric coupling in the region of the geomagnetic equator, to explain the EIA features observed in this study.
Recent investigations show that there are a number of specific effects at F-region altitudes which could be considered as earthquakes ionospheric precursors. One of such effects is a night-time increase of F2 critical frequency 1 to 2 days before the seismic event. Distortions of the electron density profiles which occur at the same time are investigated in this report. N(h)-profiles obtained from vertical soundings near the epicenter differ noticeably from IRI predictions.