Low Frequency (LF) Radio Sounding for Ionospheric Remote Sensing and Earthquake Prediction (Case Study: a few Earthquakes in North-West Iran)

Abstract

This paper presents the first low-frequency (LF) radio sounding in Iran for earthquake prediction and ionospheric remote sensing purposes. Two LF signals transmitted from Türkiye (162 kHz) and Tajikistan (252 kHz) are recorded in Tehran. The recorded data in 2019 is studied in detail. The diurnal variation of the LF signal is averaged over a one-month period to remove temporal variations as a result of background ionospheric irregularities as well as pre-seismic anomalies. The capability of the International Reference Ionosphere (IRI) model in explanation of the time evolution of the received signal is examined. The morning and evening termination time manifested from the amplitude of the received LF signal is compared against the variation of electron density obtained along the transmitter-receiver great circle path. It has been shown that simple comparison of the averaged electron density along the signal propagation path from the transmitter to the receiver coold be used to estimate the electron density during sunset and sunrise. A comprehensive method to advance the IRI estimation of the current state of the ionosphere is proposed. The LF signal anomalies associated with four earthquakes (EQ) near the propagated LF signals at 162 kHz from Türkiye to Tehran are investigated. The anomalous behavior of the LF signal within +/-15 days of the EQ is studied. Daytime variation as well as sunrise and sunset offset in days approaching each event is explored as a possible indicator of pre-seismic activity. The characterization of the LF radio signal and the possibility of earthquake prediction within the Iran plateau are discussed.