PRE-SEISMIC IONOPSHERIC ANOMALIES FROM GNSS OBSERVATIONS: STATISTICS ANALYSIS AND CHARACTERISTICS

Up to now, it is still difficult to obtain reliable precursors and to understand the detail and nature of earthquakes from traditional technique observations. Nowadays, the ionospheric total electron content (TEC) from ground-based global navigation satellite systems (GNSS) and space-borne GNSS Radio Occultation can be used to investigate the seismo-ionospheric disturbances, which may provide insights on the earthquake. In this paper, seismo-ionopsheric anomalies from GNSS observations are investigated, particularly for recent bigger earthquake of the 2011 Mw 9.1 Tohoku Earthquakes and global earthquakes with Mw= 5.0 from 1998 to 2014. Obvious disturbances in TEC are found about 4 hours before the main shock of 2011 Tohoku earthquake. Comparing to pre-seismic effects, post-seismic is more apparent. In addition, statistical analysis of 10-day TEC data before global Mw= 5.0 earthquakes shows significant enhancement 5 days before an earthquake of Mw= 6.0 at a 95% confidence level. Sharpness in cumulative percentages is evident in seismo-ionospheric disturbance prior to Mw= 6.0 earthquakes. The relative values reveal high ratios (up to 2) and low ratios (up to -0.5) within 5 days prior to global earthquakes for positive and negative anomalies. The anomalous patterns in TEC related to earthquakes are possibly due to the coupling of high amounts of energy from earthquake breeding zones of higher magnitude and shallower focal depth.