Temporal and spatial distribution of GPS-TEC anomalies prior to the strong earthquakes

Abstract

Earthquakes are one of the most destructive and harmful natural disasters, especially in recent years, the 2008/5/12 Wenchuan M7.9 earthquake, the 2011/3/11 Tohoku M9.0 earthquake and the 2012/4/11 Sumatra M8.6 earthquake have caused a significant impact to the human life. In this paper, we make a study of the temporal and spatial distribution of the Global Positioning System Total Electron Content (GPS TEC) anomalies prior to the three strong earthquakes by the method of statistical analysis. Our results show that the pre-earthquake ionospheric anomalies are mainly positive anomalies and take the shape of a double-crest structure with a trough near the epicenter. The ionospheric anomalies do not coincide with the vertical projection of the epicenter of the subsequent earthquake, but mainly localize in the near-epicenter region and corresponding ionospheric anomalies are also simultaneously observed in the magnetic conjugate region prior to the three earthquakes. In addition, the amplitude and scale-size of the ionospheric ΔTEC are different with the magnitude of the earthquake, and the horizontal scale-size of the greatest anomalies before the Tohoku M9.0 earthquake is ∼30∘ in longitude and ∼10∘ in latitude, with the maximum amplitude of TEC disturbances reaching ∼20 TECu relative to the background. The peak of anomaly enhancement usually occurs in the afternoon to sunset (i.e. between 14:00 and 18:00 local time) which lasts for approximate 2 hours. Possible causes of these anomalies are discussed, and after eliminating the effect of solar activities and magnetic storms it can be concluded that the detected obvious and regular anomalous behavior in TEC within just a few days before the earthquakes is related with the forthcoming earthquakes with high probability.