Composite regional catalogs of earthquakes in the former Soviet Union (Open-File Report 2002-500)
Seismological study of the territory of the former Soviet Union developed in the 20th century with the approach of maintaining constant observations with standard instrumentation and methods of data processing, determining standardized parameters describing the seismic sources, and producing regular summary publications. For most of the century, event data were published only in Russian and were generally unavailable to the Western scientific community. Yet for many regions of this vast territory, earthquakes with magnitudes less than 2 were routinely located and characterized, especially since the early 1960s. A great volume of data on the seismicity of the Eurasian landmass is therefore available, although to date only in scattered publications and for incomplete periods of time.
To address this problem, we have undertaken a comprehensive compilation, documentation and evaluation of catalogs of seismicity of the former Soviet Union. These include four principal, Soviet-published catalog sources, supplemented by other publications. We view this as the first step in compiling a complete catalog of all known seismic events in this large and important region. Completion of this work will require digitizing the remaining catalogs of the various regional seismological institutes.
To make these data more useful for regional seismic investigations, as well as to be consistent with their provenance, we have prepared Composite Regional Catalogs, dividing the territory of the former Soviet Union into 24 regions. For each of these regions, all the data available from the basic catalog sources (see below) have been combined and evaluated. Note that, for regions with low seismicity, the historical (non-instrumental, macro-seismic) data are of increased importance. Such information, if not included in any summary, were taken from various publications and marked as "historical".
A Brief History of Seismological Study in Russia and the Former Soviet Union
The first substantial summary of earthquakes in Russia and adjacent territories was the catalog of I.V. Mushketov and A.P. Orlov , which was based solely on macroseismic data. The beginning of regular seismic observations in Russia was marked by the issuance of a noteworthy publication --the Bulletin of the Permanent Central Seismological Commission (or PCSK), published in 1902-08 under the direction of G.V. Levitskaya. Being aware of imperfections in the seismic instrumentation used at that time, the compilers of the PCSK Bulletin did everything possible to preserve the main quantitative characteristics of these records -the amplitude and duration of vibrations- in the most complete form. Macroseismic data were collected under the direction of the PCSK, and were combined with instrumental data in a separate publication, in order to simplify the use of the materials in the PCSK Bulletin.
From 1908 to 1928, periods and amplitudes were published in the first Soviet summary bulletin of the network of seismic stations. Because of the exceptionally high quality of seismogram analysis, reflected in the individual bulletins of the best seismic stations (e.g., Pulkovo and the independent stations of Anapa, Grozniy, Pyatigorsk, Samarkand and others), it is still possible to calculate accurate earthquake magnitudes for events in this time period. Beginning in 1923, the bulletins of the individual seismic stations were published in Moscow by the Institute of Physics of the Earth.
By 1911, macroseismic observations were being separated from instru-mental data, and their publication in the bulletins became of secondary importance. Macroseismic data were collected and analyzed, but published independently, without cross-reference. Eventually, however, the boom in construction brought to the forefront the problem of seismic risk, and aroused new interest in historic strong earthquakes. In these early years, the Caucasian seismologist Eu.I. Bius compiled an exceptionally detailed and complete catalog of Earthquakes In Transcaucasia, and a number of other data collections were published. Changes were also made to the summaries of instrumental data. For example, the inability to accurately calculate true ground displacement was considered sufficient reason to remove the dy-namic characteristics of waves from event summaries.
A landmark publication was the 1962 Atlas of Earthquakes in the U.S.S.R, a compilation and presentation of earthquakes that occurred in the period of 1911-1957. This volume, which included a catalog of seismicity and detailed maps, served to summarize this early period in the development of Soviet observational seismology.
After the 1948 devastating Ashkabad earthquake, the expansion of the seismic network was undertaken, as well as the replacement of the seismographs of the Nikiforov system with what were then the advanced broadband seismographs of the Kirnos system (CK). This created a new foundation for improving the analysis of observations. Substantially more precise calculation of amplitude of ground displacement soon made it possible to incorporate the earthquake magnitude into seismological practice. After 1956, the sensitivity of seismic stations was been further increased and the dynamic and frequency ranges of the recorded signals was widened. Short-period seismographs of high sensitivity were installed at the network stations, as well as long-period instruments and seismographs for recording strong ground motions. In the 1970s the sensitivity of the equipment increased again, with the dynamic range of instruments increasing to 100 dB. An increase in the number of stations was accompanied by unification and standardization of seismic observations.