Results of Geomagnetic Studies on the Problem of Forecasting Strong Earthquakes in Uzbekistan

The article is devoted to the problem of forecasting strong earthquakes by the geomagnetic method. The geomagnetic method is widely used on this problem in seismically active regions of the world as one of the promising, informative and operational geophysical methods. The results of long-term geomagnetic studies on the problem of forecasting strong earthquakes in Uzbekistan are presented. Geomagnetic studies were carried out on the territories of the Tashkent, Ferghana, and Kyzylkum geodynamic polygons in the epicentral zones of strong earthquakes that occurred. Long-term, medium- and short-term precursors of earthquakes have been identified. Anomalous changes in the geomagnetic field associated with the decline in aftershock activity were also revealed. The dependence between the duration of the manifestation of long-term magnetic precursors and the magnitude of earthquakes is determined. Absolute proton magnetometers MMP-1, MV-01 (Russia), and G-856 (USA) were used to measure the geomagnetic field.

Forecasting changes of hydrological and hydrochemical conditions in the Aral Sea

The increase of irretrievable river water withdrawals and regulation of river flow has a negative effect on the natural regime of the Aral Sea. The Ainu Darya River and the Syr Darya River Basins are the largest irrigated farming areas. Their favorable soil and climatic conditions ensure guaranteed yields of various crops on irrigated lands. Since 1961, for the drastic increase of irretrievable river water withdrawal, mainly for irrigation, the inflow of fiver water into the Aral Sea has started to decrease significantly, accordingly the sea＇s hydrological and hydrochemical regimes disrupted dramatically. The sea level has continued to drop as evaporation exceeds inflow. This negatively transforms the natural environment and worsens socio-economic conditions in Priaralie as a whole, especially in the lower reaches of Amu Darya and Syr Darya, where natural conditions are largely determined by the sea＇s impact. At present, this causes desertification of the nonirrigated zone in the deltas, spreading to new areas as the Aral Sea dries out.

Analysis of the geomagnetic field and vertical movement near the intersection of Karjantau and Tavaksay faults in Uzbekistan

Based on the previous researches of geophysics and geodesy,this paper analyzes the geomagnetic field and surface vertical movement near the intersection of Karjantau and Tavaksay faults by using the highprecision magnetic survey technique.Due to the high accuracy of the magnetic survey technique,the magnetic anomalies associated with geological structures and discontinuities are revealed.The measurement results of high-precision total station show the vertical movement difference of observation points over 36 years.When processing the obtained data,the points(Ferma and Visota)are identified as the most mobile points in the Karjantau fault zone.At the points(Skala and Visota)in the north of the Karjantau fault,the observed settlements are-1 mm and-59 mm,respectively.At the southern geodetic observation points(Noviy,Kladbishi and Ferma),they are uplifted by 32 mm,11 mm and54 mm,respectively.Based on these data,we can see that in the Tavaksay geodynamic polygon area,the variation of vertical movement values around the Ferma and Visota points is greater than other places.The reason for this phenomenon is that the above points are located in the areas close to the deep Karjantau fault zone.

Assessment of strain effect of strong-motion (focus) zones of earthquakes on earth＇s surface displacement

Strain effect of focal zones on fore-seismic displacements of earth＇s surface is studied in the paper for real conditions of focus zones of the earthquakes. The width of the interval of maximum displace- ments is determined by the conditions of potential focus of tectonic earthquake. The solution of elastic problem for half-space with soft inclusion is used. Calculations are conducted also by empirical formulas, obtained for similar stress states. Possible radius of the zone of maximum revelation of strain anomaly is determined on the basis of the growth of rupture scale and change in heterogeneity volume. It is shown that obtained expression covers a wider range of magnitude variations with consideration of the interval of scale change in upcoming rupture-forming zone. In the example of Tashkent （1966） and Gazli （1984） strong ground motions, an analysis of possible strains occurrence on the Earth＇s surface was conducted.

Models(form)of long-,medium-and short-term earthquake precursors

Through analysis and generalization of more than 50 years of monitoring data pertaining to geomagnetic earthquake precursors in landfills across Uzbekistan involving repeated route and area surveys and stationary observations,as well as extensive data retrieved from the study of the complex in foreign countries,models of long-,medium-and short-term earthquake precursors were created for the first time.Medium-and short-term data were mainly studied based on monitoring data of the precursor complex considering geodynamic polygons in Uzbekistan.The analysis demonstrated that these precursors exhibit different shapes,configurations and signs.There occurred no uniform precursor form.Precursors exhibited bay-shaped forms,including both positive and negative signs,in addition to stepped,wave-oscillatory and other formats.The variety of manifestation forms primarily depends on the surrounding regions’geological and tectonic structures and the various processes in the Earth’s crust.