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2 Acta Geophysica

2 2021

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

Mahmoudian A., Saravani Ghayour A.

Acta Geophysica

2021

Vol. 69, no. 5

1585--1595

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.

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

2021

Vol. 69, no. 4

1545--1566

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.