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Tien-Shan Earthquakes Catalog

#KR-536


Tien-Shan Earthquakes Catalog and Seismic Activity of Kyrzyz Territory

Tech Area / Field

  • ENV-SEM/Seismic Monitoring/Environment

Status
3 Approved without Funding

Registration date
21.06.2000

Leading Institute
Institute of Seismology, NAS, Kyrgyzstan, Bishkek

Supporting institutes

  • Institute of Dynamics of the Geosphere, Russia, Moscow\nKyrgyz-Russian Slavonic University, Kyrgyzstan, Bishkek

Collaborators

  • Columbia University / Lamont-Doherty Earth Observatory, USA, NY, Palisades\nEnterprise Oil Gulf of Mexico Inc., USA, TX, Houston\nMaxwell Technologies, USA, VA, Reston\nHarvard University / Department of Earth and Planetary Sciences, USA, MA, Cambridge

Project summary

Principal goal of the study is to compile a complete catalog for Tien-Shan seismic events by internationally accepted standards and to reveal principal characteristics of seismic condition in the territory of the Kyrgyz Republic.

Importance and actuality of the study is related to high seismic activity of intra-continental Tien-Shan mountain system. Characteristics of seismic regime in the zone of intra-continental mountain creation are of scientific and practical interest. The Kyrgyz Republic territory (within a "box" confined by = 39 - 44 N, = 69 - 81 E) is a large part of the Tien-Shan. There are yearly observed about 4,000 earthquakes with seismic magnitude above ML >1.6 occurring inside the territory. The largest historical earthquakes are Chilik (1889, M=8.4) and Kemin (1911, M=8.2). There were also several large-scale earthquakes in Kyrgyz Republic during last decade: Baisooroun (1990, M=6.1), Kochkor-Ata (1992, M=6.1), Suusamyr 1992, M=7.3) and Koshdobin (1997, M=6.0). Total economic loss from these earthquakes exceeds 50,000,000 USD.

Tien-Shan earthquakes catalog provides original experimental material for accurate assessment of seismic risk for particular regions, living areas and large-scale constructions within Central Asia Republics. Investigation of numerous problems of the Earth's inner structure, modern geodynamics of Asia, physics of earthquake source mechanism, and many others is based on original seismological data. Completeness and reliability of a seismological catalog play a crucial role in accuracy of seismic risk assessment and anti-seismic constructions theoretical and experimental research. Thus, seismological catalog is a solid basement for theoretical and applied seismological investigations.

Development and improvement of seismological network capabilities within Tien-Shan region have been leading to progressively lower energy of representative earthquakes and increasing number of estimated parameters. The first seismic station was opened in Tashkent in 1901, and then in 1927 in Bishkek and Almaty. In 1991 American scientists (IRIS Corporation) deployed a telemetric seismic network KNET containing 10 broadband seismic stations in the northern part of Kyrgyzia.

In addition to the development of seismological network from 1927 described above, parameters of large-scale historical earthquakes (location, date, and macroseismic features) were determined by historical and archeological data and by seismo-deformations. For this period of time, earthquakes' seismic magnitude MLH and depth were determined by macroseismic parameters.

Level of representative earthquakes with reliable occurrence rate and other parameters was progressively lowered: from 1929 to 1949 - М LH 5, from 1950 to 1961 - МLH 3.6, from 1962 to 1975 - МLH 3.0, from 1976 to 1984 - МLH 2.3, and from 1985 - МLH 1.6. Telemetric seismological network KNET provide data for catalog processed in US and Kyrgyz Republic containing events with МLH 0.2.

Kyrgyz seismological service has constructed iso-intensity maps for 50 earthquakes with МLH 5. These data are published in "Atlas of USSR earthquakes"(1962), "New catalog " (1977), "New catalog …" (1982), and annual issues of "Earthquakes in the USSR" for the period from 1962 to 1991, special volumes "Earthquakes of Central Asia and Kazakhstan " for 1992-1995. Improvement of seismic observations, development of new procedures of earthquake parameters' determination, and study of macroseismic data demand continuous re-evaluation of the seismological data set. Correction of some portions of the catalog is done by obtaining new data from neighboring countries, including China, as well as by teleseimic data from international data centers. Such catalogs are published ( Kondorskaya at al. (1993); "Catalog", 1997, Omor&Peres, 1999).

There is information on source mechanisms of kyrgyzain earthquakes with М 5.0 beginning from 1938. Since 1990 source mechanisms are determined for earthquakes with с М 3.0. Source mechanism catalog before 1998 contains solutions for 1,700 earthquakes. There are no estimates of accuracy class, however, for source mechanism of these events.

Seismic regime of the Kyrgyz Republic territory is known with an accuracy, which is provided by completeness and reliability of the Tien-Shan earthquake catalog. The non-uniform characteristics of the catalog with time complicate the investigations. It leads to controversy of opinions on many important problems. For example, one group of researchers insisted that Suusamyr and Talas depressions and mountains surrounding the depressions can be associated with a zone with maximum possible earthquake of magnitude M=6.1-7.0. Other scientists thought that maximum earthquake should be estimated as to be between magnitudes 7.0 and 7.5. In 1992 an earthquake occurred in the Suusamyr depression with magnitude M=7.3.

On the basis of the Kyrgyz seismological service catalog statistical characteristics of earthquake migration are studied as well as correlation between principal parameters of seismic events and relationships between spatial distribution of seismic structures and tectonic features and geophysical inhomogenieties.

From the very beginning of seismic observations inside Central Asia seismological service of Kyrgyz Republic has gathered an outstanding amount of original materials, including data on more than 60,000 Tien-Shan earthquakes. This information needs to be processed and compiled under unified and common standards.

The project implementation will help to achieve the following results: to compile a complete and unified bank of seismological data; to compile and publish catalog of Tien-Shan earthquakes which will include more than 30,000 events extended by their source mechanism and dynamic parameters as well as maps of iso-intensity; to analyze the catalog and to reveal correlation between principal parameters of sources; to construct models for development of seismic process within the region of intra-continental mountain creation and to establish principal statistical relationships for temporal, spatial and energy distribution of the earthquakes; to construct maps of seismic activity development within Kyrgyz Republic; to determine parameters of deformation process in the framework of the solid medium with inhomogeneity.


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