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WARNING MISSION: Background

Background of the Project

Disastrous earthquakes happen 100 to 200 times a year. World community carries out seismological, geophysical, tectonomagnetic as well as non-traditional investigations to make possible the earthquake prediction. It is believed that due to a wide web of seismic stations and earthquake prediction test sites the problem of long-term earthquake forecast has been basically solved. This means that we are able to answer rather closely where the earthquake may occur but not when. There is a chance that the data of ionospheric plasma observations hold an answer to the latter question. Satellites and ground-based facilities may detect earthquake precursors in the ionosphere a few hours or days before the main shock.
Although ionospheric parameters are primarily controlled by the helio-physical processes the perturbations which propagate from the Earth are also detectable. As it became clear last decade, both the tropospheric perturbations (storms, cyclones, peculiarities of near-Earth air circulation) and the tectonic processes (earthquakes, active fractures, subduction zones) are locally reflected in the ionospheric state. Let us consider the most reliable manifestations of seismo-ionosphere relations.
The first example of the night sky luminescence related to the earthquake was described in 373 B. C. in Rome. This phenomenon has been observed above Tashkent (1966) and Spitac (1988) before the earthquakes at the atomic oxygen spectral lines 6300 and 5577 A. Long-term observations of the air glow have confirmed its correlation to earthquake-events with an advance time from a few hours to a day.
Another set of data has been obtained by the means of vertical ionospheric sounding. Considerable variations in the effective heights of signal reflection, changing value of the critical frequencies (i.e., of the peak electron density), increasing of the number of ionograms with signatures of irregular and random anomalous radio reflections, sporadic E-layer "blurring", and other effects indicate that the preparation of earthquake is accompanied by the enhancement of plasma turbulence as well as growing amount of ionospheric plasma inhomogeneities over the seismoactive region
As far as we know the first space-born observation of earthquake related phenomena has been carried out aboard the Soviet "Intercosmos-19" satellite. Then a great deal of data have been obtained by "OGO-6", "Nimbus", "Aureol-3", "Geos-1", "Geos-2", "Intercosmos-Bulgaria-1300", "DE-2" and "Intercosmos-24" missions.
A specific noise-like VLF electrostatic emission has been detected in range of tens KHz over the earthquake epicenter within 200 to 300 km in the latitudinal direction and over a sufficiently long distance in the longitudinal direction. This emission originates about 10 to 20 hours before the main shock and lasts over about the same time after it reaching the intensity peak at the instant of the main shock. One of proposed explanations of this phenomenon anticipates the penetration of electromagnetic field from the earthquake focus into magnetosphere, interaction of this field with high-energy particles of the Earth radiation belts and subsequent excitation of VLF plasma noise. Such interpretation is supported by the particle measurements of "Aureol-3" satellite which has passed narrow region of significant increases in the precipitation of high energy (100 KeV) electrons and protons. Further seismogenic phenomena detected by satellites is local decreasing (about 20 per cent) of the ambient ion density. A possible interpretation suggests the generation of so called ionospheric bubbles (rare plasma regions) at geomagnetic field lines based on the epicenter of shocks.
ULF "Hz"-oscillations have been recorded several hours before the main shock in a narrow magnetic field tube (40...100 km along the satellite trajectory) conjugated with epicenter of the earthquake. In the case of moderate earthquake (M = 3.5...5) the magnetic field disturbances have reached magnitudes of 0.2...0.5 nT/Hz at altitudes of 800 to 900 km and frequency about 8 Hz. Probably, these disturbances propagate through the ionospheric plasma as Alfven waves.
The history of the investigations under review may be conventionally divided into three chronological stages. At the beginning anomalous of the ionospheric plasma parameters had been noted in connection with seismic activity. The next stage involved statistical verification of each phenomenon. In result, real existence of seismogenic effect upon the ionosphere has been confirmed (we emphasize this point because there are teams of investigators who prove the absence of such effect). At the moment the main theoretical problem is to explain the mechanisms of seismo-ionospheric coupling. Physics of the earthquake precursors generation is not well understood today and only qualitative speculations are used for some explanation of observation results.
Last modified March 15, 1996
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