Anomalous total electron content (TEC) and atmospheric refractivity prior to the very strong China earthquake of May 2008

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Abstract
A dual-frequency global positioning system (GPS) receiving set-up at Guwahati (26° 10′ N, 91° 45′ E), has been in operation for the last year and a half, providing total electron content (TEC) data as input for understanding pre-earthquake contributions to low-latitude atmospheric dynamics. The major China earthquake of 12 May 2008, with magnitude 8.0 and an epicentre at 31° 24′ N, 103° 58′ E is a rare event to facilitate extracting earthquake features on the TEC data, and hence low-latitude system perturbations. This paper begins with a brief discussion on the methods adopted in identifying TEC performance before an impending earthquake from ionospheric data, and presents results of analysis of the event of 12 May. TEC magnitudes recorded with latitude / longitude and elevation of satellites for every pass are linked with pre-earthquake TEC features and are used as inputs to identify epicentre position. The role of seismic-time refractive index variations is examined to explain the observed TEC characteristics.

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