Abstract
Recent ionospheric observations report anomalous total electron content (TEC) deviations prior strong earthquakes. We discuss common fetures of the pre-earthquake TEC disturbances on the basis of statistics covering 50 strong seismic events during 2005-2006. The F2-layer ionospheric plasma drift under action of the electric fields of seismic origin is proposed as the main reason of producing TEC anomalies. The origin of such electric fields is discussed in terms of the lithosphere-atmosphere-ionosphere coupling system. This theory is supported by numerical simulations using global Upper Atmosphere Model (UAM). UAM calculations show that the vertical electric current with the density of about 20 - 40 nA/m2 flowing between the Earth and ionosphere over an area of about 200 by 2000 km is required to produce the TEC disturbances with the amplitude of about 30% - 50% relatively to the non-disturbed conditions. Ionosphere responses on the variations of the latitudinal position, direction and configuration of the vertical electric currents have been investigated. We show that not only the vertical component of the ionospheric plasma drift but also horizontal components play an important role in producing pre-earthquake TEC disturbances.
Highlights
The ionosphere of the Earth is no doubt an important part of the global electric circuit and is a subject to dramatic perturbations related mainly with geomagnetic and solar activity
We present the pre-earthquake GPS-observed total electron content (TEC) disturbances analysis’ results for 50 cases of M ≥ 6 seismic events happened during 2005-2006, and propose a physical interpretation for considered seismo-ionosphere anomalies supported by the Upper Atmosphere Model (UAM) numerical calculations
As the most probable physical mechanism that produce pre-earthquake NmF2 and TEC disturbances we consider the vertical drift of the F2-layer ionospheric plasma under the influence of zonal electric field of seismogenic origin [20,21,22]
Summary
The ionosphere of the Earth is no doubt an important part of the global electric circuit and is a subject to dramatic perturbations related mainly with geomagnetic and solar activity. TEC is the total number of electrons along the vertical path between the satellite and the ground in 1 m2 cross section column; TEC is measured in TEC units (1 TECu = 1016 el/m2). Basing on numerous ground-based and satellite observations many papers reported significant ionosphere disturbances (including the TEC increases or depressions) existing during quiet periods of the geomagnetic and solar activity. As these disturbances happen just before and spatially near the earthquakes’ locations many investigators consider these ionosphere anomalies as precursors. We present the pre-earthquake GPS-observed TEC disturbances analysis’ results for 50 cases of M ≥ 6 seismic events happened during 2005-2006, and propose a physical interpretation for considered seismo-ionosphere anomalies supported by the Upper Atmosphere Model (UAM) numerical calculations
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