Statistical characteristics of seismo-ionospheric GPS TEC disturbances prior to global Mw?5.0 earthquakes (1998-2014)

Pre-earthquake ionospheric anomalies are still challenging and unclear to obtain and understand, particularly for different earthquake magnitudes and focal depths as well as types of fault. In this paper, the seismo-ionospheric disturbances (SID) related to global earthquakes with 1492. Mw. ?. 5.0 from 1998 to 2014 are investigated using the total electron content (TEC) of GPS global ionosphere maps (GIM). 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. Earthquakes with a focal depth of less than 60 km and Mw. ?. 6.0 are presumably the root of deviation in the ionospheric TEC because earthquake breeding zones have gigantic quantities of energy at shallower focal depths. Increased anomalous TEC is recorded in cumulative percentages beyond Mw. = 5.5. Sharpness in cumulative percentages is evident in seismo-ionospheric disturbance prior to Mw. ?. 6.0 earthquakes. Seismo-ionospheric disturbances related to strike slip and thrust earthquakes are noticeable for magnitude Mw6.0-7.0 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. © 2015 Elsevier Ltd.China Academy of Chinese Medical Sciences National Basic Research Program of China (973 Program): MOST 973, 2012CB72000 National Natural Science Foundation of China: 11173050, 11373059, 11573052 National Natural Science Foundation of ChinaThe authors are very gratified to IGS for providing GPS IONEX data and USGS for providing earthquake catalog. We are also thankful to NASA and Kyoto University, Japan for providing geomagnetic indices data. This research is supported by the National Keystone Basic Research Program (MOST 973) (Grant no. 2012CB72000 ), National Natural Science Foundation of China (NSFC) Project (Grant nos. 11173050 , 11373059 and 11573052 ) and Key Laboratory of Planetary Sciences, Chinese Academy of Sciences, China