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Study of local ionospheric plasma perturbation induced by pre-seismic activities

Mahmoudian A., Saravani Ghayour A.

Acta Geophysica

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2021

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Vol. 69, no. 5

1585--1595

EN

The pre-seismic ionospheric anomalies coupled through well-proposed lithosphere–atmosphere–ionosphere processes are known to cause pre-seismic ionospheric disturbances (PIDs). The present paper investigates the regional variation of ionospheric densities in the Iran area with the purpose of anomalous ionospheric detection. The ionospheric reference model (IRI) is employed to examine the accuracy of such empirical models for typical TEC (total electron content) values in Iran to determine any deviation from the normal ionospheric state. Two strong consecutive earthquakes with a magnitude of larger than 6 in the northeast of Iran were selected along with the GPS data from 5 ground stations within 50 km of the epicenter. The local ionospheric plasma density mapping using the GPS signal for earthquake prediction is studied. The results show a very promising temporal variation of local ionospheric plasma between the stations from 4 weeks to almost a week leading to the event. The deviation of TEC from the mean value between the fve stations shows no enhancement or suppression of local plasma rather than a plasma motion. A very quiet PID signature could validate the lithosphere– atmosphere–ionosphere coupling (LAIC) process associated with pre-earthquake geochemical and dynamical mechanisms. To validate that the analyzed time period falls on the minimum of solar activity, the observed positive anomalies in the regional TEC correspond to fuctuations to pre-earthquake activity and not to geomagnetic activity, and the Kp and Dst indices are taken into consideration.

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On the signifcance of requisite criteria in detecting pre earthquake ionospheric precursors: a case study of the Tohoku earthquake of March 11, 2011

Chukwuma Victor U., Adekoya Bolarinwa J., Thomas Jewel E., Emah Joseph B., Oloruntola Racheal F.

Acta Geophysica

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2021

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Vol. 69, no. 4

1545--1566

EN

In the advent of the Tohoku earthquake (Mw 9.1 occurred at 14:46 LT on March 11, 2011), the Japan Meteorological Agency issued earthquake early warning announcements to the general public; however, there were problems with the precision of the early warning systems. This early warning systems issue, and the scale of consequential loss of human, material and technological resources of the Tohoku earthquake and those of about 57 earthquakes with magnitude M ≥ 7.5 from August 2008 to August 2018 around the world compel a need for investigation for detection of some signals before the earthquake that should be examined and interpreted as a precursor by examining the changes in the ionospheric phenomena. In this light, discrimination of pre-earthquake ionospheric anomalies of seismic origin from those of other drivers is essential for understanding, justifcation and physical interpretation of the earthquake precursors phenomena. Presently using a set of criteria that adequately diferentiates pre-earthquake anomaly of seismic origin from those of other sources, this study has shown concordant results with the existing studies namely that foF2 data obtained from 8 Chinese and Japanese stations revealed signifcant enhancements 2–6 days before the Tohoku earthquake and that the anomalies extended to 2774 km from the epicentre, thereby underscoring the necessity of requisite criteria in detecting pre-earthquake ionospheric precursors. Furthermore, the study suggests that the anomalous variations observed during periods of earthquake preparation are of seismo-magnetosphere origin.

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Features of the ionosphere behavior before the Kythira 2006 earthquake

Zakharenkova I.E., Shagimuratov I.I., Krankowski A.

Acta Geophysica

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2007

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Vol. 55, no. 4

524-534

EN

In this paper we present specific features of TEC (total electron content of the ionosphere) behavior as possible precursors of Kythira (Southern Greece) earthquake of January 8, 2006 (M6.8). For this purpose, we used both the TEC data of GPS-IGS stations nearest to the epicenter, and TEC maps over Europe. The favorable circumstance for this analysis was the quiet geomagnetic situation during the period prior to the earthquake. One day before the earthquake, a characteristic anomaly was found out as the day-time significant increase of TEC at the nearest stations, up to the value of 50% relative to the background condition. To estimate the spatial dimensions of seismo-ionospheric anomaly, the differential mapping method was used. The ionosphere modification as a cloud-like increase of electron concentration situated in the immediate vicinity of the forthcoming earthquake epicenter has been revealed. The amplitude of modification reached the value of 50% relative to the non-disturbed condition and was in existence from 10:00 till 22:00 UT. The area of significant TEC enhancement had a size of about 4000 km in longitude and 1500 km in latitude.

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Response of the ionosphere to the Baltic Sea earthquake of 21 September 2004

Krankowski A., Zakharenkova I., Shagimuratov I.

Acta Geophysica

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2006

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Vol. 54, no. 1

90-101

EN

GPS observations of the European permanent network were used to identify seismoionospheric precursors of Baltic Sea earthquake of 21 September 2004. It is a very rare event for this region of Europe (magnitude of about 5.0). This value is the threshold for the occurrence of seismic effects in the ionosphere. In total electron content (TEC) data over the region of the earthquake, a specific ionospheric anomaly appeared one day before the earthquake was detected. The ionospheric variability had a positive sign with an enhancement of about 4-5 TECU (1 TECU = 1016 electrons/m2) relative to the non-disturbed state of the ionosphere. The anomaly had a duration of 4-5 hours in the day time. The special size of this anomaly was about 1000 km. The characteristic parameters of the anomaly show that it can be associated with ionospheric precursors of an earthquake.