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Seismology and Seismic Engineering


First written information sources for earthquakes on the territory of the country refer to I Century BC when an earthquake torn Chirkman Plateau and buried in Black See the antique city of Bizone (Kavarna). For the whole pre-seismological period before 1891 information relatively limited in number historical chronicles and documents had reached us, containing mainly pieces of information and descriptions regarding strong earthquakes which had happened on our lands.

The beginning of the organized and systematic studies on the earthquakes in Bulgaria is founded in 1891 by Acad. Spas Vatsov, who is the founder of the Bulgarian Meteorology and Seismology. He consecutively accomplished the expansion of the seismological research works within the activities framework of the Central Meteorological Station (C.M.S.) in Sofia, which he managed since 1890.

In chronological order below stated are given only the most important moments from the development of the seismological research in Bulgaria. They could be grouped in three man stages.

I. Non-instrumental stage (1891-1904 г.)

1891 – Sp. Vatsov organized correspondent network for collecting information for the earthquakes felt on our territory.
1892 – Beginning of the systematic gathering and processing of macroseismic information from C. M. S.
1902 – Publishing of the first book of Sp. Vatsov from the series “Earthquakes in Bulgaria in ХIХ Century”. The book contained the instruction of observing earthquakes with insignificant additions compared to the original one dated 1894. Under the editorship of Sp. Vatsov consequently the books “Earthquakes in Bulgaria” from N 2/1901 in 1903 г. to N 14-17/1913-1916 in 1923 are published.
1903 – 1903 Bulgaria became member of the International Seismological Association; Sp. Vatsov participated in its second Congress meeting in Strasburg.
1904 – On 4th of April in the valley of Struma River the strongest earthquake in our country took place (magnitude 7.8, intensity of 10 rate scale) which gave impetus for organizing of instrumental observations in Bulgaria; the first popular earthquakes publication was made (A. Ishirkov, Student Review Magazine); first publication abroad regarding the earthquake in the valley of Struma River by Grablovits (G.Grablovitz, Italy).

II. Stage of primary instrumental observations and scientific research (1905-1959)

1905 – First seismic station is founded in Sofia (φ=42°42′ N, λ=23°20′ E) in the building of C. M. S., subsequently in the Faculty of Natural Science and Mathematics in proximity of Vasil Levski Monument.
1907 – Edition N1 of the Seismological Bulletin is published concerning Sofia station registrations in 1905; the bulletin is edited by Sp. Vatsov and the reports are made by St. Staikov.
1912 – St. Staikov published in Italy the first theoretical work on determination of the earthquake centre by macroseismological data; seismograph Omori-Bosh with weight of 25 kg was mounted in station Sofa.
1913 – On 14th of June destructive earthquake in G. Oryahovitsa – V. Tarnovo took place as St. Staikov performed the first detailed field observation research published in 1917; publications for the earthquake by G. Bonchev and P. Bakalov.
1917 – Earthquake in Sofia on 18th of October with intensity of 7-8 level; the full research works of R. Ivanov were published in 1931.
1927/28 – Unique leveling was performed before and executed once again after the devastating earthquakes in Maritsa valley; the results were published by K. Yankov in 1945; Ch. Richter used them in his book “Elementary seismology” ( 1958) as one of the little such examples in the world.
1928 – On 14th, 18th and 25th of April destructing earthquakes in the valley of Maritsa River took place; numerous field research works were executed followed by publications of K. Kirov ( 1928-1935), G. Bonchev ( 1928), St. Bonchev and P. Bakalov (1928), Y. Zelkov (1929), N. Penchev (1930), Directorate for supporting victims of earthquakes – DIPOSE (1931) and other; publication are made as well by foreign researchers such as W. Mihailovich (J.Mihailovic, 1933)
1930 – Posthumously the book of St. Staikov “Building materials for the seismology of Bulgaria, Trakia and Macedonia” – basic literature for earthquake history in the country.
1934 – K. Yankov mounted in station Sofia on 1st of October a bi-component mechanical horizontal seismograph Vihert with weight of 1000 kg, period 9-11s, magnification about 200 times (with air attenuation), which sets the beginning of the more modern registration allowing examining as well of the dynamics of the seismic waves.
1938 – K. Yankov published generalization research “ Seismic manifestations in Bulgaria”
1942 – K. Yankov and N. Genadiew mounted in March in seismic station Sofia a bi-component mechanical horizontal seismograph Krumbach (Iena) for registration of near earthquakes: with weight of each component 100 kg, period 1-3s, magnification to 100 times (with air attenuation).
1951 – As of 1st of January Seizmology Office was separated from the Meteorology and is transferred by Counsel of Ministers Ordinance Nо2185/27.VII.1950 to the Main Directorate for Geological and Mining Research.
1955 – In station Sofia the first three-component seismograph Krumbach started functioning, constructed to register earthquakes of near proximity: two photo-optical horizontal components and vertical galvanometric seizmograh (own period about 2 s and magnification 2500-3000 times)
1956 – Prof. I. Petkov started presentations of extended lecture course on General Geophysics and Seismology for the students-physicists of the Sofia University St. Kliment Ohridski, two volume course is published in 1968.
1957 – First well-grounded seismological zoning of the country (K. Kirov, E. Grigorova); first operative Regulations for Projecting and Construction in earthquake areas (first attempt for such Regulations dated 1947).

III. Stage of expanding of the scientific research and modernization of the observation network (since 1960)

1960 – Under the initiative of Acad. L. Krastanov the Geophysical Institute of BAS is established (Counsel of Ministers Ordinance dated 11.XI.1959); the Seismological Office of the Geophysical Researches was transferred in the Institute and since 1st of August the Section “Seismology” was established; in station Sofia was installed the first modern galvanometric tree-components seismograph type SK, construction by Prof. D.P. Kirnos and upgraded since 1.IX.1964 with his participation in the first long-period seismograph SKD with magnification above 1000 times in Bulgaria.
1961 – The first detailed and microseismic zoning was performed in the region of Kardzhali Damp with the participation of S.V. Medvedev and Bulgarian specialists; the second Bulgarian seismological station was established in Dimitrovgrad; the first book was published on anti-earthquake stability of the buildings in the country.
1965 – The third seismic station “Pavlikeni” was launched in exploitation– equipped with the first in the country high sensitivity short-period seizmographs with magnification 50 000 times; the rated magnitude scale for near and far earthquakes was finalized.
1968 – The forth seismological station started operations in Kardzhali; new and complete energetic and cinematic data were published for the strong and destructive earthquakes in the country after 1900; the magnitude scale was supplemented with the assessments on the continuity of the seismic variations.
1970 – The Balkan seismological project was launched for execution leaded by Dr. W. Karnik (V. Karnic, Check Reublic); first moving seismological station was created in UAZ vehicle; The Third Congress of the European Commission on Anti-earthquake Engineering was carried out in Sofia.
1971 – Temporary seismological station in Vitosha started operations.
1972 – The first accelographs type SMA-1 were mounted in part of the seismological stations for registration of strong earthquakes.
1973 – In the Geological Institute section “Seizmic mechanics” was established which since 1982 became a separate Laboratory of BAS.
1974 – First major results were published from the Balkan seismological project including the first united Balkan seismological catalogue; the construction of the underground part of the Vitosha Observatory was finalized and modern seizmographs were mounted for registration of weak and strong, far and near earthquakes.
1977 – Profound research works were performed on the effects and consequences from the earthquake on 4th of March in Vrancha; seismological station in Plovdid starts functioning, first attempts were made to construct seismographs in Bulgaria.
1978 – Telemetrical transmition on analog seismographic information was realized via radio by UKV from Salzitza Hut (Vitosha Mountain) to the building of the Geophysical Institute with experimental apparatuses developed in the Institute (Sp. Delistoyanov); seismological station Musomishta started operations; arrival and training in Bulgaria of the first foreign specialists on Seismology.
1979 – The prognostic seismological zoning of the country was finalized by large team under the leading management of Acad. E Bonchev; the seismological station Precelency starts operations; the construction of the Vistosha Observatory was finalized as it turned to be the best equipped and with high sensitivity seismological station in the country and South-East Europe; the first ionospheric early-warning predictors were documented for the earthquake of 4th of March in Vrancha (Romania).
1980 – Modern National operative telemetric system for seismological information (NOTSSI) was created with which the level of registration and processing achieved could be compared with the best systems in the world.; the first model research for optimization of the seismological network was realized; building up of an observation network had started for registration of strong movements via accelographs (72 accelographs type SMA-1 and few apparatuses SMA-2 and SMA-3); the first foreign post-graduate students on Seismology were trained in Bulgaria.
1981 – Under NOTSSI an Automated seismological centre started operations based on mini-machine PDP 11/34; foundation of archive with digital data for near earthquakes; a programme was developed for complex prognosticate ground for searching early-warning detectors in the central part of the country – Ground “Sofia-Plovdiv”.
1982 – The first stage of developments on prognostication of the consequences from future strong earthquakes in the country was finished.
1985 – Bibliographical catalogue of the Geophysical Institute was published for the period 1960-1985 containing full record on the published works on seismology from Bulgarian authors; primary research works on electromagnetic early-warning detectors in Bulgaria; projects were developed for several new seismological stations under NOTSSI: Lukovit, Strazhitsa, Razgrad.
1987 – The new normative Regulation for Projecting and Construction of Buildings and Facilities in Earthquake Regions came into force, in which as Ground was used the prognostic map of earthquakes for the period of 1000 years; three-dimensional model for lithosphere for the central part of the Balkans was proposed.
1988 – Bulgaria hosted the XXI General Assembly of the European Seizmological Commission from 23rd to 27th of August in National Palace of Culture, Sofia; 30 reports by Bulgarian authors were presented; generalized monography was published for the structure of the Earth crust in Bulgaria (Hr. Dachev).
1991 – The construction of underground and over-ground part of the modern seismological observatory in Plovdiv was finalized – planned to be a back-up centre of NOTSSI.
1995 – Under NOTSSI were added two newly constructed local seismological networks in Provadia and Kozlodui.
2002 – Conception for the creation of new map of the seismological zoning of hazardous type is developed as a foundation for implementation of the European anti-seismic norms (Eurocode 8).
2006 – Complete modernization of the National Seizmological Network (NSN) was realized as modern electronic seizmographs and digital systems were used for transmission of signals from the seizmological stations to the Centre, and the registration, processing and archiving of data were executed by specialized computer system.

In the above events succession as well the most important steps could be marked to follow for development and improvement of the observations and analysis of the seismicity in national scale. In the first place is the step to increase the number of the seismological stations – their distribution density is not enough for the effective research of the low seismicity on the whole territory of Bulgaria – only the central part of the county is well covered. Of great scientific and social importance is the construction of prognostic complex for research of various kind of early-warning predictors for strong earthquakes in the country – since 1980 the necessary funding for which construction could not be ensured.