Earth Planets Space, Vol. 63 (No. 7), pp. 853-857, 2011
Lucie M. Rolland1, Philippe Lognonné1, Elvira Astafyeva1, E. Alam Kherani2, Naoki Kobayashi3, Michéle Mann1, and Hiroshi Munekane4
1Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, UMR 7154 CNRS, F-94100 Saint-Maur, France
2Instituto Nacional de Pesquisais Espaciais (INPE), São Jose dos Campos, São Paulo, BR-12227010, Brazil
3Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara City, Kanagawa 252-5210, Japan
4Geospatial Information Authorithy of Japan, 1 Kitasato, Tsukuba 305-0811, Japan
(Received April 11, 2011; Revised June 10, 2011; Accepted June 11, 2011; Online published September 27, 2011)
We provide here a preliminary analysis of the ionospheric perturbations observed after the 11 March 2011 Tohoku Earthquake using a GPS-derived Total Electron Content (TEC) technique. Such anomalies are routinely observed after seismic events of magnitude Mw = 6 and more. Here, we use the high density and the wide coverage of the Japanese Global Positioning System (GPS) network GEONET to image the ionosphere just after the main shock. We describe ionospheric perturbations with exceptional extension in amplitude and duration. As already seen in earlier events, a first intense signal is observed about 10 minutes after the seismic rupture; the first response consists in two modes: one propagating beyond 3 km/s and the other at nearly 1 km/s. A further analysis of TEC time series of the latter mode near the source shows the typical frequencies of acoustic resonance. Beyond 400 km from the source, both the tsunami induced gravity wave and a third mode are imaged, the latter for the first time. We show that the pattern of this slow (225 m/s ± 10 m/s) and long period gravity wave (1.8 ± 0.2 mHz) is most visible in the North-West of the epicentral area. This description is corroborated by a computation of the normal modes of the solid Earth-atmosphere system.
Key words: GPS-TEC, earthquake, ionosphere, acoustic resonance.