Ionospheric phenomena before strong earthquakes

A statistical analysis of several ionospheric parameters before earthquakes with magnitude <i>M</i> <u>></u> 5.5 located less than 500 km from an ionospheric vertical sounding station is performed. Ionospheric effects preceding &quot;deep&quot; (depth <i>h</i> > 33 km) and &quot;crust&quot; (<i>h</i> <u><</u> 33 km) earthquakes were analysed separately. Data of nighttime measurements of the critical frequencies <i>fo</i>F2 and <i>fo</i>Es, the frequency <i>fb</i>Es and Es-spread at the middle latitude station Dushanbe were used. The frequencies <i>fo</i>F2 and <i>fb</i>Es are proportional to the square root of the ionization density at heights of 300 km and 100 km, respectively. It is shown that two days before the earthquakes the values of <i>fo</i>F2 averaged over the morning hours (00:00 LT–06:00 LT) and of <i>fb</i>Es averaged over the nighttime hours (18:00 LT–06:00 LT) decrease; the effect is stronger for the &quot;deep&quot; earthquakes. Analysing the coefficient of semitransparency which characterizes the degree of small-scale turbulence, it was shown that this value increases 1–4 days before &quot;crust&quot; earthquakes, and it does not change before &quot;deep&quot; earthquakes. Studying Es-spread which manifests itself as diffuse Es track on ionograms and characterizes the degree of large-scale turbulence, it was found that the number of Es-spread observations increases 1–3 days before the earthquakes; for &quot;deep&quot; earthquakes the effect is more intensive. Thus it may be concluded that different mechanisms of energy transfer from the region of earthquake preparation to the ionosphere occur for &quot;deep&quot; and &quot;crust&quot; events

foF2 seismo-ionospheric effect analysis: actual data and numerical simulations

Abstract. On the background of seasonal and helio-geomagnetic disturbances, disturbances of the ionization density near noon connected to earthquakes are investigated. The study is performed for some tens of earthquakes with magnitudes M>5 and depths h<70 km, which occur at distances from the vertical sounding stations "Tokyo", "Akita", and "Yamagawa" not larger than R=exp(M)+150 km. The analysis is performed using data registered by the three sounding stations every hour during 30 years. Especially methods of the statistical analysis are applied to search for regularities in the lithospheric-ionospheric links before and after earthquakes. The growth of the mean ionization density N at the F-layer electron density maximum Fof2 five-three days before earthquakes, and the decrease of N approaching the eruption and during a few days after the earthquake is investigated in dependence on both the magnitude of the earthquake M and the ionization density N near the F-layer maximum. It is found that some days before earthquakes the decrease of the ionization density ΔN is proportional to the values of M and N. After the earthquakes, ΔN depends much weaker on the magnitude M, and it is not influenced by the ionization density N. The variations of the ionization density three days before earthquakes do not depend on N and M (within the same order of approximation)

On the possible influence of radon and aerosol injection on the atmosphere and ionosphere before earthquakes

International audienceA model of the generation of pulses of local electric fields with characteristic time scales of 1?10 min is considered for atmospheric conditions above fracture regions of earthquakes. In the model, it is proposed that aerosols, increased ionization velocity and upstreaming air flows occur at night-time conditions. The pulses of local electric fields cause respective pulses of infrared emissions. But infrared emissions with time scales of 1?10 min were not observed up to now experimentally. The authors think, that the considered non-stationary field and radiation effects might be a new-type of applicable earthquake indicators and ask to perform special earth-based and satellite observations of the night-time atmosphere in seismoactive fracture regions

Daytime variations of foE connected to earthquakes

Abstract. In the present work it is shown that, in accordance with the observations of the vertical sounding station "Tashkent", the critical foE-frequency of the daytime E-layer increases about one day before winter-earthquakes with magnitudes M > 5 and depths of the epicentre of h < 60 km, which appeared at distances of R < 2000 km from the station. The reliability of the result is larger than 99 %. The phenomenon is not observed for summer-earthquakes. It seems to be determined by the atmospheric wind system. Further, the variations of the foE-frequency are compared with possible simultaneous variations of the critical frequency foF2 of the F2-layer. First results show that only very large changes of the ionisation density in the E-layer influence the ionisation density in the F-region. Therefore, no synchronous growth of the foE- and foF2-frequencies 1–2 days before seismic shocks could be observed

On variations of <i>fo</i>F2 and F-spread before strong earthquakes in Japan

International audienceThe statistical analysis of the variations of the dayly-mean frequency of the maximum ionospheric electron density foF2 is performed in connection with the occurrence of (more than 60) earthquakes with magnitudes M>6.0, depths hRfoF2 decreases before the earthquakes. One day before the shock the decrease amounts to about 5%. The statistical reliability of this phenomenon is obtained to be better than 0.95. Further, the variations of the occurrence probability of the turbulization of the F-layer (F spread) are investigated for (more than 260) earthquakes with M>5.5, hRfoF2 analysis, the Wolf number is less than 100 and the index SKp is smaller than 30, and in case of the F-spread study a Wolf number less than 80 and SKp smaller than 17 are chosen

IR spectral analysis for the diagnostics of crust earthquake precursors

Some possible physical processes are analysed that cause, under the condition of additional ionisation in a pre-breakdown electric field, emissions in the infrared (IR) interval. The atmospheric transparency region of the IR spectrum at wavelengths of 7–15 μm is taken into account. This transparency region corresponds to spectral lines of small atmospheric constituents like CH&lt;sub&gt;4&lt;/sub&gt;, CO&lt;sub&gt;2&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt;O, NO&lt;sub&gt;2&lt;/sub&gt;, NO, and O&lt;sub&gt;3&lt;/sub&gt;. The possible intensities of the IR emissions observable in laboratories and in nature are estimated. The acceleration process of the electrons in the pre-breakdown electrical field before its adhesion to the molecules is analyzed. For daytime conditions, modifications of the adsorption spectra of the scattered solar emissions are studied; for nighttime, variations of emission spectra may be used for the analysis