TITLE:
Unusual Change in Critical Frequency of F2 Layer during and Prior to Earthquakes
AUTHORS:
Soujan Ghosh, Sudipta Sasmal, Subrata Kumar Midya, Sandip K. Chakrabarti
KEYWORDS:
Earthquake Early Warning, Wave Propagation, Earthquake Interaction, Forecasting and Prediction, Ionosphere/Atmosphere Interactions, Electrical Properties
JOURNAL NAME:
Open Journal of Earthquake Research,
Vol.6 No.4,
October
19,
2017
ABSTRACT: 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 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 variation. We
also observe significant changes during aftershock events. The solar geomagnetic
indices were found to be low which ensures that these anomalies in F
Parameter are due to seismic events.