Parrot, M.

A systematic multi-parameter and multi-platform approach to study the slow process of earthquake preparation is fundamental to gain some insights on this complex phenomenon. In particular, an important contribution is the integrated analysis between ground geophysical data and satellite data. In this paper we review some of the more recent results and suggest the next directions of this kind of research. Our intention is not to detect a particular precursor but to understand the physics underlying the various observations and to establish a reliable physical model of the preparation phase before an impending earthquake. In this way, future investigation will search for suitable fore-patterns, which the physical model of multi-layers coupling predicts and characterizes by quasi-synchronism in time and geo-consistency in space. We also present alternative explanations for some anomalies which are not actually related to earthquakes, rather to other natural or anthropic processes.

Ionospheric data obtained from the DORIS system are used in this paper. The DORIS system is composed of several ground-based beacons which emit at two frequencies (400 MHz and 2 GHz) and of receivers on board several satellites (currently SPOT2, SPOT4, SPOT5, Topex-Poseidon, Jason1 and Envisat). Thanks to the density of its network coverage (∼50 stations), DORIS provides information on the ionosphere. The TEC (Total Electron Content) parameter which is the electron density integrated over the vertical could be obtained from DORIS measurements. In a first step, the paper describes the way to obtain the TEC data from the DORIS ionospheric measurements, and comparisons of the results are done with the IRI2001 model. In a second step, TEC values are used to search for correlation between ionospheric perturbations and seismic activity. Earthquakes of magnitude larger than 5 are chosen close to the ground-based DORIS stations. Among other results, the statistics show that, during the night time and at geomagnetic latitude close to the equator (<10°), TEC amplitude fluctuates at the time of the earthquakes as it is expected, but also 2 days and 5 days before.

The magnetosphere-ionosphere-thermosphere subsystem is strongly coupled via the electric field, particle precipitation, heat flows and small scale interaction. Satellites in situ measurements and ground based complex diagnostics can provide comprehensive coverage of both time and geomagnetic place effects. Human activity also can perturb Earth s environment, but few are connected with controlled experiments in the ionosphere and are transient. Most of them are related to industrial activity and have increased in recent years. The most important power sources are broadcasting transmitters, power stations, power lines and heavy industry. At ionospheric altitude some disturbances and physical processes are related to seismic activity, thunderstorm activity and some global changes in the Earth environment such as ozone holes. Various natural and artificial indicators can affect satellite telecommunication quality. The aim of this presentation is to report progress in understanding the physical processes in the ionosphere described above and to assess the application of these considerations to the study of plasma effects on Earth-space and satellite-to-satellite communication.