Pre-earthquake Ionospheric anomalies monitored by GPS TEC,
Liu, J. Y., Y. J. Chuo, S. J. Shan, Y. B. Tsai, S. A. Pulinets, S. B. Yu (2004),
Ann. Geophys., 22 p. 1585–1593,
10.5194/angeo-22-1585-2004.