Ionospheric anomalies related to strong earthquakes in North America as observed by TEC

Abstract

Research studies have recently illustrated a plausible relationship between seismic activity and ionospheric disturbances. To elucidate seismo-ionospheric disturbances, we analyzed the temporal and spatial characteristics of ionospheric disturbances associated with large earthquakes that occurred in North America. We selected two strong events with M >= 6.5 that took place in 2009 and 2010 during the solar minimum. We used the United States total electron content (US-TEC) measurements as a main dataset, and the changes in the TEC were compared with the variations in the topside plasma density measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite. Positive or negative TEC anomalies were observed before (as a precursor) and after the earthquakes. In addition, we found that positive anomalies occurred more frequently than negative ones. Although TEC anomalies occurred at all local times, strong anomalies usually appeared from late afternoon to dawn (16-6 local time). Seismic activity-related TEC anomalies were typically limited to the earthquake region, whereas geomagnetic activity-related TEC anomalies were observed over a vast region. Furthermore, local TEC anomalies occurred over a long period of 20 days preceding and succeeding the earthquakes, in contrast to those associated with geomagnetic activities which occurred concurrently with the geomagnetic disturbances. Additionally, most abnormal increments in the electron density obtained by the DEMETER satellite over the seismic zone coincided with the TEC anomalies. Thus, the variations observed in the TEC and topside electron density before and after these two earthquakes suggest that these ionospheric disturbances are related to seismic activities. (C) 2021 COSPAR. Published by Elsevier B.V. All rights reserved.