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Abstract
On 12 May 2008 at 06:28 UT a major earthquake of magnitude 8.0 struck Wenchuan County (31.0° N, 103.4° E) in southwest China. Ionospheric total electron content (TEC) values, derived from a network of 58 global positioning system (GPS) receivers over China and nearby countries, were used to investigate the ionospheric precursor of the great earthquake. The observations revealed that there was an anomalous enhancement in TEC (100% increase on the 15-day median) during the afternoon–evening sector on 9 May 2008 while geomagnetic conditions were quiet (Kp ≤ 2). The TEC variations on the west side and east side of the epicentre show large dissimilarity on 9 May 2008. By constructing the longitude/latitude TEC map, the distribution of the region predominated by increased TEC values was shown to be localized at longitudes 90–130° E. Our results suggest that this abnormal enhancement was most possibly a seismo-ionospheric signature.
Acknowledgment
This research was supported by the National Natural Science Foundation of China (40804041) and the Key Technology Research and Development Program of China (2008BAC35B02) and Fund of IES Scientific Research Program (02092414). The authors acknowledge the Institute of Earthquake Science China Earthquake Administration and the China Meteorological Administration for providing the GPS data. The geomagnetic indices were obtained from the World Data Center C2 for Geomagnetism in Kyoto. The Kp and F 10.7 indices were downloaded from NGDC database (www.ngdc.noaa.gov), and solar wind data were downloaded from the Coordinated Data Analysis Web (www.cdaweb.gsfc.nasa.gov).
