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LABORATORY «GEOPHYSICAL METHODS OF EARTHQUAKE ZONES»

Head: Pogrebnoy Valentin, Doctor of Physical and Mathematical Sciences,

One of the main tasks in the complex research of the Institute of Seismology, National Academy of Sciences, is the study of speed and deep structure of the crust and upper mantle in connection with the seismicity. Without knowledge of the structure of the environment in which earthquakes can not be knowledge of nature geodynamic processes.

Е.А. Розова 
Е.А. Rozova,
Academician KSSR

Work on the study of the velocity structure of the crust and upper mantle of the Tien Shan are directly linked with the name of academician E.A. Rozova (1899-1971 gg.) - The organizer and head of Seismology of the Kyrgyz SSR. Under the leadership of E.A. Rozova (1952-1971 gg.) Division are working on the characterization of hypocenters earthquakes occurring in the territory of Kyrgyzstan and neighboring areas, a detailed study of seismicity. In 1962 - 1967 years. detailed seismological observations were made in the areas of projected dams: Toktogul, Kirov, Papan. Since 1967, detailed seismological observations are made in the area of ​​Chu hollow and its mountain frame. At the same time she headed the laboratory of theoretical seismology, as a result of which received the first presentation on the deep structure of the crust in Central Asia. It has been proposed three-layer velocity model, based on which the classical concepts of layered homogeneous crust Tien Shan replaced conclusions about the more complex its structure.         

In 1975, the laboratory was renamed to the laboratory for studying the structure of the crust (Head. Lab. K.g.-m.n. Bisengaliev I.M.). From 1984 to 2008 he headed the laboratory corresponding member of National Academy of Sciences, Prof. Sabitova T.M. With its name is associated with the development of modern methods of seismic tomography for detailed studies of speed irregularities of the earth's crust. In 1989, on the basis of scientific co-operation of scientists of the Institute of Seismology, National Academy of Sciences, the Institute of Physics of the Earth and the Rensselaer Polytechnic Institute of the USA for the first time in Central Asia were used seismic tomography methods for studying the Earth's crust of the Tien Shan, which made it possible to develop a three-dimensional velocity model Orogen to the depth of 65 ~ km. Since 1998, the laboratory staff has worked to refine and detail this model. The greatest contribution to the development of high-speed models have working Sabitova TM, Adam AA Medzhitovoy Z.A. In 2006, based on a greatly expanded data sample (30,000 arrivals of P waves and the arrival of 20 000 S-waves from the 5450 earthquake) has developed a new three-dimensional model of the Earth's crust, covering a large area of ​​research and a depth of 225 km.

From left to right: Adam A., Corresponding Member of the National Academy of Sciences, Sabitova T.M., Z.A. Medzhitova

Interpretation of the calculated three-dimensional velocity model, in addition to information about the structure of the speed of the Tien Shan allowed to approach the knowledge of complex geodynamic processes in the study region, in particular, the seismicity and its relationship with the velocity structure of the lithosphere. Using a new three-dimensional model has allowed, for example, to determine the depth of the main areas and zones of weakness (waveguides) in the crust of the Tien Shan, within which the probability of strong earthquakes.

Since 2008, the laboratory in connection with the expansion methods to study the deep structure of the crust and upper mantle of the Tien Shan (magnetometry, gravimetry) was renamed the "Laboratory of geophysical methods for studying the seismic zones" (Head. Lab. Prof. , Pogrebnoy V.N.). Particular attention is paid to the study of the structural features of the seismogenic zones are genetically related to the faults of the crust and upper mantle of different ranks.

Laboratory staff conducted studies of the geophysical and seismic tomography fields, distribution of seismicity and territorial situation of deep faults. The signs reflect faults in the fields of geophysical and seismic tomography, which are used to identify and determine the structural features of faults visually observable and hidden without exiting to the surface.

From left to right: Bagmanova N.H., Pogrebnoy V.N., E.L. Mirkin, Grebennikov V.V., Volkova T.

Key achievements:

  1. Designed three-dimensional velocity model of the Tien Shan lithosphere along the longitudinal (P) and transverse (S) seismic waves down to depths of 225 km on the basis of records of regional and teleseismic earthquakes, industrial and nuclear explosions.
  2. It was found that the crust of the Tien Shan orogen is different from the surrounding crust more stable regions of low velocity structure of the middle and lower parts of the crust.
  3. A significant velocity heterogeneities in the crust and mantle, primarily weakened zones. In the cortex - a region of decreasing speed or gradient with depth in the mantle - subvertical zones of abnormally low speeds.
  4. It is concluded that the formation of zones of strong earthquakes in the Tien Shan is directly connected with high-speed irregularities of the earth's crust and upper mantle, and above all - in the presence of low-speed deep mantle anomalies. This fact can be used as a criterion for allocation of zones of possible earthquake sources (PES).
  5. Identify signs reflect faults and fault zones in geophysical fields that identify and clarify territorial and structural position of both visible and hidden faults.

                                                                                

A schematic map of the anomalous (∆Т) and field at the junction
Chu basin and its mountain frame.

The research results are used in the lab complex methods of seismic hazard assessment in the Kyrgyz Republic.

Over the years, the laboratory carries out work on projects financed by foreign grants research funds Soros (1995, 1996). And the International Science and Technology Center - ISTC (1998-2001 and 2003-2006.). The research results were published in the well-known overseas ("Physics of the Earth", "Geology and Geophysics», «Geophysical Research», and others.) And national magazines ("Science and New Technologies", "Proceedings of National Academy of Sciences", "Proceedings of the universities") and presented at international forums and conferences.