Analysis of Ionospheric Anomalies Before the 2013 Mw6.4 Iran Earthquake

On April 9, 2013, a large earthquake of Mw=6.4 occurred near the Bushehr, Iran. This paper investigates preearthquake ionospheric anomalies during the earthquake period. A clear anomaly that occurred on April 8 lasted 6 hours. Eliminating ionospheric anomalies that may have been caused by solar activities and magnetic storms, we believe that a positive anomaly on April 9 was very possibly an ionospheric precursor. The affected ionospheric area on April 9, which is evident on a vertical total electron content distribution map, extended to 51.5° inlongitude and 28.5° in latitude. The anomaly peak arose from 15:00–19:00 LT, and its location did not coincide with the vertical projection of the epicenter, but was instead to its south. Corresponding ionospheric anomalies are also observed in the magnetically conjugatedregion. There were no obvious ionospheric anomalies in other parts of the world. To analyze changes in the ionospheric anomaly, computerized ionospheric tomography technology was used to invert the spatial and temporal distribution of electron density in the ionosphere. Theionospheric anomaly on April 9, 2013 is suggested to be an ionospheric precursor of the April 9 earthquake in Iran.