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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Radio observations with IS3 for earthquake precursors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer There is, perhaps, not a single month in the year that news agencies of the world do not report terrible news about earthquakes. They suddenly fall on settlements, entire regions, bring catastrophic destruction associated with huge material losses and irreparable human casualties. According to the UN, the loss of property from earthquakes is estimated at up to 10 billion US dollars a year. Of course, it is impossible to prevent seismic natural disasters, but to be prepared for them means to significantly reduce their consequences. Is a reliable long-term or at least short-term forecast of earthquakes possible? Science is getting closer and closer to a positive answer to this question. This is evidenced, in particular, by many years of experience in radio observations of earthquake precursors from the IS3 board, accumulated by the Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN). By now, scientists have come to the firm conviction that an earthquake is not a sudden event, but a process that is preceded by a variety of geophysical phenomena. In seismically active areas at the time of the earthquake and immediately before it, the glow of the atmosphere, soil, mountain slopes, disturbances in the atmospheric electric potential, variations in the intensity of electromagnetic radiation at distances up to a thousand kilometers from the epicenter, as well as changes in the critical frequencies and density of E and F layers of the ionosphere were repeatedly observed. In the 3s, with ICXNUMX, bursts of low-frequency electromagnetic noise emissions were detected over the epicenters of large earthquakes a few hours before the event, a sharp burst of pulsed electromagnetic radiation was recorded in a fairly wide frequency band. Currently, the study of seismoionospheric effects is proceeding in two directions: the analysis of individual events and the derivation of statistical regularities. Let us dwell on radio emissions in the sound frequency range as the precursors of earthquakes. It became possible to draw such a conclusion because it was possible to compare the state of precursors in the process of growth and direct manifestation of seismic events with radio emissions in a calm state. Studies of background radio emissions in the audio frequency range (0,1 ... 20 kHz) have been carried out in our country with IC3 for many years. They continue even now. Usually, a broadband receiver and devices were used to register them, which made it possible to perform spectral analysis of several frequency lines on board the IC3. Registration with broadband receivers is suitable for the study of discrete signals and a detailed study of the spectrum of noise and quasi-noise radiation. The use of onboard spectrum analyzers provides information on the absolute intensity and spatial distribution of the radiation intensity. Reception of broadband information transmitted to the Earth is carried out in the observatories of Russia, Germany, the Czech Republic, Hungary when satellites fly over them. The long lifetime of the satellites and the large amount of data obtained made it possible to accumulate a significant amount of homogeneous information suitable for statistical processing and comparison of variations in the intensity of electromagnetic low-frequency noise emissions under various conditions of geomagnetic and solar activity. Diurnal, latitudinal, and altitude variations in the intensity of low-frequency radiation were obtained in absolute units, and their dynamics was traced under different conditions of geomagnetic disturbance. All this information about the "background" radiation was a reliable basis for the subsequent study by the author of these lines, who for the first time managed to detect the effect of excitation of low-frequency noise over the alleged epicenter of the expected earthquake. An analysis of the information obtained during a series of successive satellite passes makes it possible to obtain the spatiotemporal distribution of the recorded parameters. Variations in the magnetic (m) and electric (e) components of the field of noise low-frequency radiation from the output of the channels of the spectrum analyzer at frequencies of 4650, 800, 450 and 140 Hz were recorded; changes in the thermal plasma concentration Ne and the flux density of energetic electrons with energies Ee over 40 keV and Ee over 100 keV. All this shows the diversity of manifestations of seismic activity at satellite altitudes in near-Earth outer space. How do the recorded low-frequency electromagnetic radiations that precede the event, during the main shock and after it, manifest themselves and signal about earthquakes? The figure shows in geographic coordinates the projections of the orbits (4080...4087) of the Interkosmos-19 satellite in the northern and southern hemispheres during the IC3 flybys near the earthquake epicenter. In this case, bursts of intensity of the low-frequency radiation field were observed. The location of the epicenter is marked on the diagram (xx). In the upper and lower parts of the diagram, in addition to the world observation time, the time before (minus sign) and after (plus sign) the earthquake is indicated. On the projections of the orbital turns, the filled rectangles show an increase in the signal intensity of the magnetic (to the right of the trajectory projection) and electric (to the left of the projection) components of the radiation field by 20 dB relative to the level of background noise usually observed in this region of space. The image in the diagram refers to a frequency of 4650 Hz, but similar bursts are noted in the entire band of recorded frequencies. The amplitude and especially the time of observation of bursts increase as we approach the epicenter in longitude and in time. Before the earthquake, changes were observed in comparison with the variations in the magnetic and electric components of the radiation field that are usually recorded in this region; after the earthquake, the electric component prevailed. Bursts of noise were also noted in the magnetically conjugate region, but the observation zone was significantly narrower.
Previously, we obtained data on the global spatiotemporal distribution of the intensity of natural (daily, latitudinal, and altitude variations in absolute units) low-frequency radiation at frequencies of 3 Hz and 19 kHz under various conditions of geomagnetic disturbances. This indicates the reliability of the signal extraction method for determining the development of seismic activity. This is also proved by observations of electromagnetic radiation from two satellites passing over the epicenter of the same earthquake. The Interkosmos-Bulgaria-1300 satellite flew over the epicenter of the earthquake on January 21, 1982 at an altitude of 800 km 12 minutes before the main shock at a distance of 2,8° in longitude. In this case, quasi-harmonic oscillations of the magnetic field with an amplitude of 3,5 nT were recorded. The size of the oscillation registration zone was 40...100 km along the trajectory. The Orel 3 satellite flew at an altitude of 1970 km near the epicenter of the same earthquake 4 h 48 min before the main shock. On board, bursts of low-frequency radiation field intensity in the range of 10 Hz ... 20 kHz were also noted. The presence of consecutive measurements from two satellites over the same area before the earthquake, despite the differences in the equipment used, allows us to conclude that seismomagneospheric noises are present for a long time in the area above the epicenter before the mainshock, which confirms the possibility of using these noises for forecasts. According to satellite observations, we analyzed not only individual events, but also obtained statistical characteristics. At the same time, we introduced some restrictions: rather strong earthquakes with a magnitude M of more than 5,5 and a depth of less than 60 km were selected. Only relatively low-latitude earthquakes (geomagnetic latitude less than 45°) were taken into account. As a result, it was found that the latitudinal size of the burst detection zone is significantly larger than the longitudinal one, i.e., bursts of radiation are observed in the form of a "noise belt" extended along the geomagnetic latitude of the epicenter. Before the earthquake, both the magnetic and electric components of the noise emission field were recorded. After the earthquake, the electrical component dominated. The frequency range is from fractions of a hertz to 20 kHz, and maybe even higher (20 kHz is the upper range of the equipment). The reliability of the observed effect, calculated on the basis of the results of statistical processing of experimental results, is 85 - 90%. Thus, the effect of excitation of electromagnetic radiation in the plasmasphere above the epicenter of the expected earthquake was discovered and confirmed. Theoretically, the reality of the registered phenomenon is confirmed. Naturally, the scientific approach cannot be limited to the observation of one phenomenon. Therefore, the main attention was paid to a comprehensive analysis of earthquake precursors, including low-frequency radiation, and variations in energetic electron fluxes above the expected epicenter. The assumption about the relationship of these phenomena with seismic activity, first expressed by IZMIRAN specialists almost ten years ago, was confirmed by studying the results of observations in different periods of time. For example, immediately before the Spitak earthquake on December 7, 1988, a vertical cosmic ray telescope mounted on a balloon and launched about 41 min before the main shock recorded an increase in the flux of penetrating particles under the influence of the forthcoming earthquake. According to the data obtained from the Oreol 3 satellite, simultaneous bursts of the intensity of low-frequency radiation (0,01 - 20 kHz) and the count rate of the energetic particle flux over the earthquake epicenter were recorded 4 hours and 48 minutes before the main shock. It was found that out of 20 cases of increased precipitation of particles accompanied by intense bursts of low-frequency radiation, in 18 cases the anomalous bursts coincided with the presence of earthquakes. The satellite "Interkosmos 19" also recorded simultaneously observed anomalous variations in the intensity of low-frequency noise and the flux density of energetic particles. Thus, when an earthquake occurs, the entire plasmasphere is excited above the epicenter and in the magnetically conjugate region. The generalization of scientific observations by domestic and foreign specialists makes it possible to draw up a diagram of the temporal development of geophysical phenomena that accompany the manifestation of seismic activity. Let's call them:
All the above information confirms the possibility of earthquake prediction, for which both ground-based and satellite data should be used in combination. It seems optimal and possible even now to organize satellite monitoring of earthquake precursors, to create a network of autonomous ground stations connected via a telemetric channel with satellites. The combined information could be processed in a data center. It is unlikely that the costs of creating such a network will be excessive compared to the losses that sudden, but in fact predictable natural disasters bring with them. Author: V. Larkina, Doctor of Phys.-Math. Sciences, Moscow
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