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Tien-Shan Tectonics

#KR-357


Active Faults and Strong Earthquakes in Tien-Shan

Tech Area / Field

  • ENV-SEM/Seismic Monitoring/Environment

Status
8 Project completed

Registration date
10.06.1999

Completion date
29.10.2004

Senior Project Manager
Rudneva V Ya

Leading Institute
Institute of Seismology, Kyrgyzstan, Bishkek

Collaborators

  • University of Arizona, USA, AZ, Tucson

Project summary

The project goal is to study the structure, kinematics, and dynamics of modern active faults in Tien Shan Mountains (TSM) and their relations with strong earthquakes, and to reveal details of continental mountain construction and processes of seismic catastrophes.

The project importance is connected to the large number of active faults and strong earthquakes in the TSM area. Earthquakes result in large destruction and human victims (eg. Suusamyr earthquake with M=7.3, 1992). Continental mountain belts, similar to TSM, create also a problem for the new global tectonic theory.

Latest and modern active faults serve as boundaries between tectonic lithospheric blocks of various hierarchical level. The location of stuctural elements (including faults of various ranks) only does not allow to construct the structural and geodynamic model of a given area of the lithosphere. The existent technique of the morpho-structural analysis can not reveal the unique pattern of tectonic blocks and their ranking at the background of multiple discontinuities. Errors in the block ranking result in misinterpretation of the block system model. Consequently it prevents to find proper interrelations between structural elements, crust and mantle deformational processes, and various geological, geochemical, and geophysical processes related to seismicity of the area.

The TSM system originated far from the main tectonic belt at the area of the Indian and Euroasian plate collision. The TSM system extends for 2000 km in a sub-latitude direction having width of 300 to 500 km. The TSM system is conjugated at the south margin with the Tarim plate, Pamir mountain system and Tadjik depression, and at the north margin with Kazakh shield and Turan plate. As a lithospheric block TSM is surrounded with Tarim, Pamir, Tadjik, Kazakh, and Turan blocks. The boundaries are constructed by active faults.

In regions of active faults of inner and outer zones of TSM the paleodeformations generated by strong paleo-earthquakes are widely presented. It means that strong paleo-earthquakes were related to active zones across TSM. The location of strong historical earthquakes differs of locations of paleo-earthquakes. Strong historical earthquakes were observed in the Western part of the TSM West of the Talas-Fergana fault, as well in the inner and outer part of the TSM. East of the Talas-Fergana fault strong historic earthquakes occured in the outer TSM areas, while the inner TSM area was seimically inactive for a long period. In the northern part of TSM (so called North- Tien-Shan seismic zone) the number of earthquakes observed during the last 100 years: Belovodsk, 1889 (M=6.9), Verny, 1887 (M=7.3), Chilik, 1869 (M=8.3), Kemin, 1911 (M=8.2), Kemin-Chilik, 1938 (M=6.9), Sarykamysh, 1970 (M=6.8), Zhalanash-Typ, 1978 (M=7.1), Suusamyr, 1992 (M=7.3).

The analysis of distributions of faults and strong earthquakes of the Central Asia reveals four systems of crossing faults of various ranks. The fault system may be presented as a net with nodes. The node spacing is 570 ± 110 km, 270 ± 100 km, 120 ± 60 км, and 50 ± 15 km for different fault ranks. One can assume that the system of faults and tectonic blocks controls the local geodynamics, including seismicity of the area.

The records of wide-band seismic stations KNET (USA) cover the whole territory of Kyrgyz Republic allow to study spectra of close to source seismic waves, generated by earthquakes in the TSM region. The preliminary analysis shows that kinematics, dynamics as well as depth and structure of a discontunity generation is reflected in spectra of seismic waves.

Our experience in the data processing of seismic waves, generated by underground nuclear explosions shows that the properties of fault zones and their deformational characteristics can be established. The relationship between the deformation characteristics, the scale, and structure of fault zone may be found. As the result of the study, we can outline the active fault system, and construct the block hierarchical model of several areas of the Earth crust. We conducted similar researches during the study of the influence of the fault tectonics in the area of Kazakhsatn shield on the generation and propagation of seismic waves created by underground nuclear explosions of a wide yield range at the Semipalatinsk Test Site.

The project goals are:


- construct the model of the structure and evolution of faults and tectonic blocks;
- estimate possible influence of fault and blocks systems on the seismic wave fields;
- estimate deformational characteristics of active faults in the Northern Kyrgyzstan;
- construct the concordant block model of the Northern Kyrgyzstan;
- reveal the characteristics of the interaction between TSM and Kazakhstan shields;
- reveal rules of location and preparation of strong earthquakes;
- study general characteristics of an intra-continental mountain belt and its evolution;
- construct the geodynamic model of the modern stage of the TSM evolution;
- make the next step in the understanding of a nature of the intra-continental mountain formation in the TSM zone.


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