Investigation of TEC and VLF space measurements associated to L'Aquila (Italy) earthquakes - Stangl, G.; Boudjada, M. Y.; Biagi, P. F.; Krauss, S.; Maier, A.; Schwingenschuh, K.; Al-Haddad, E.; Parrot, M.; Voller, W. (Nat. Hazards Earth Syst. Sci., 2011)