Near-seismic effects in ULF fields and seismo-acoustic emission: statistics and explanation

International audiencePreseismic intensification of fracturing has been investigated from occurrence analysis of seismo-acoustic pulses (SA foreshocks) and ULF magnetic pulses (ULF foreshocks) observed in Karimshino station in addition to seismic foreshocks. Such analysis is produced for about 40 rather strong and nearby isolated earthquakes during 2 years of recording. It is found that occurrence rate of SA foreshocks increases in the interval (-12, 0 h) before main shock with 3-times exceeding of background level in the interval (-6, -3 h), and occurrence probability of SA foreshocks (pA~75%) is higher than probability of seismic foreshocks (ps~30%) in the same time interval.ULF foreshocks are masked by regular ULF activity at local morning and daytime, nevertheless we have discovered an essential ULF intensity increase in the interval (-3, +1 h) at the frequency range 0.05-0.3 Hz. Estimated occurrence probability of ULF foreshocks is about 40%. After theoretical consideration we conclude: 1) Taking into account the number rate of SA foreshocks, their amplitude and frequency range, they emit due to opening of fractures with size of L=70-200 m (M=1-2); 2) The electro-kinetic effect is the most promising mechanism of ULF foreshocks, but it is efficient only if two special conditions are fulfilled: a) origin of fractures near fluid-saturated places or liquid reservoirs (aquifers); b) appearance of open porosity or initiation of percolation instability; 3) Both SA and ULF magnetic field pulses are related to near-distant fractures (r<20-30 km); 4) Taking into account number rate and activation period of seismic, SA and ULF foreshocks, it is rather probable that opening of fractures and rupture of fluid reservoirs occur in the large preparation area with horizontal size about 100-200km

Scattering wideband pulse signals by non-smooth surfaces

Processes of scattering and reflection of wideband signals by non-smooth rough surfaces in the frequency range of 38–52 GHz have been investigated. Dependences of reflection coefficient for various non-smooth surfaces versus distance up to the antenna and the degree of roughness of the sample surface have been obtained experimentally. The influence of behavior and the degree of surface heterogeneity on the value of the reflection coefficient has been estimated using results of the measurements, the influence of spatial orientation of the scattering surface on amplitude of the reflected signal has been revealed

Experimental investigation of horn antenna radiation

Horn antennas are widely used in different practical applications. They serve as feed antennas in many types of more complex constructions of antennas. The horn antennas are powerful means of high energy technology, they are used as applicators in medical purposes. The horn antennas are the most popular probing device in non-destructive testing. The horn antennas are also important tools of standards of power gain. In all applications the information about of space distribution of electromagnetic field is very important. For instance in medical and technological applications knowledge of field distribution allow ones to control the depth of heating that is very important for success of operation. The feature of these applications is use of near-field wave. Information about longitudinal distribution of field serves for increasing accuracy in non-destructive testing due to more accurate calibration at the same distances for structure under test and metallic standard mirror. Usually they cannot be positioned in the same place under technological process and displacement courses error in calibration and therefore errors in dielectric constant and thickness. Power gain can be measured using metallic plate but this approach is simple only for far-field zone, for Fresnel zone a few sets of measurements at a few distances are need. This circumstance determines importance of the field description

Analysis of natural frequency and q-factor estimation for open dielectric resonators with variation of coupling by means of fractional-rational approximation of reflection response

The analysis of the natural frequency and estimation of Q-factor of the open resonator by means of fractional-rational approximation of the reflection response has been considered. An advantage of the proposed technique in comparison with the classical methods has been demonstrated. Dependence of Q-factor of the shielded half-disk dielectric resonator and estimations of the poles and the zeros of the resonance response against the coupling coefficient value has been analyzed