Institute of Geophysics, Geodesy and Geography, Bulgarian Academy Of
Total Page:16
File Type:pdf, Size:1020Kb
National Institute of Geophysics, Geodesy and Geography Seismicity and seismic hazard modeling for Bulgaria D. Solakov, S. Simeonova National Institute of Geophysics, Geodesy and Geography National Institute of Geophysics, Geodesy and Geography Bulgarian seismic network and foreign stations used in epicenter location National Institute of Geophysics, Geodesy and Geography RO-BG transboarder project DACEA Stations included in Early Warning System (Bulgarian part) National Institute of Geophysics, Geodesy and Geography Sismicity in Bulgaria and surroundings (M 4.0) National Institute of Geophysics, Geodesy and Geography Epicentral map for Bulgaria and surroundings (after 1980, all recorded quakes) National Institute of Geophysics, Geodesy and Geography Historical earthquakes The first well documented earthquake on the territory of Bulgaria is the first century BC quake occurred in the Black Sea near the town of Kavarna. 1892 г. – earthquake near the town of Dulovo, maximal intensity Imax=VIII MSK, magnitude 6.6-7.0. Observed effects in NE Bulgaria and SE Romania 1901 – An earthquake with M=7.2 was realized in Shabla region. Maximal intensity X MSK. The earthquake caused heavy destructions along the sea side between the towns of Balchik and Shabla. The felt area approximately is 610 000 km2. National Institute of Geophysics, Geodesy and Geography . In 1913 – near the town of Gorna Oryahovitsa occurred an earthquake with MS=7.0, epicentral intensity – IX-X. Destructions - Gorna Oryahovitsa, up to 95%; V. Tarnovo, Dolna Oryahovitsa, Lyaskovets -up to 80%. Felt area is about 400 000 km2 National Institute of Geophysics, Geodesy and Geography Along the Maritca valley (central part of Bulgaria), in 1928 a sequence of three destructive earthquakes occurred (the strongest earthquake is of magnitude M=7.0). Many towns and villages were strongly affected. 74000 buildings were completely destroyed and 114 people killed. They caused two surface coseismic ruptures, each of them several tens of kilometers in length. On some places the ground displacement reaches up to 1.5-2 m. National Institute of Geophysics, Geodesy and Geography However, no such large earthquakes occurred in Bulgaria since 1928. The 1986 earthquake of magnitude MS=5.7 occurred in the central northern Bulgaria (near the town of Strazhitza) is the strongest quake after 1928. 1986 – two earthquakes in the region of Strazitsa, 21.02.1986, M=5.3 and 07.12.1986, M=5.7. Partially or totally destroyed – 15000 buildings, 2 victims, 60 injured. The earthquake was felt in the area of 180 000 km2. National Institute of Geophysics, Geodesy and Geography 04.03.1977 Vrancea intermediate earthquake, M=7.2, depth 90- 110 km, epicentral intensity VIII-IX. Partially or totally destroyed – 8470 buildings, 125 victims. The heavy consequences are due to non adequate housing constructions and bad local site conditions. National Institute of Geophysics, Geodesy and Geography SEISMIC ZONING MAP 1961-1964 First building code - 1957 SEISMIC ZONING MAP 1977 National Institute of Geophysics, Geodesy and Geography SEISMIC SOURCES SEISMIC ZONING MAP – 1987, return period 1000 years 7.6-8.0 7.1-7.5 6.6-7.0 6.1-6.5 5.6-6.0 5.1-5.5 4.6-5.0 4.1-4.5 4.1-4.5 4.6-5.0 4.1-4.5 4.1-4.5 4.1-4.5 4.6-5.0 4.6-5.0 4.6-5.0 4.1-4.5 4.1-4.5 4.6-5.0 4.6-5.0 National Institute of Geophysics, Geodesy and Geography PROBABILISTIC SEISMIC HZARD ASSESSMENT The probability that a ground motion parameter, Z, at a given site, will exceed a specified level, z, during a given time period, t, is given by the expression: P(Z z | t) = 1 - e- (z)t (z)t where (z) is the average frequency during time period t at which the level of ground motion parameter Z exceeds z at the site, resulting from earthquakes in all sources in the region. The frequency of exceedance, (z) is calculated by: u m (z) (m0 ) f (m) f (r | m)P(Z z | m,r)drdm n n m0 0 n(mo) is the frequency of earthquakes on source n above a mo (min. mag. of ing. Importance); f(m) is the PDF for events between mo and maximal event for the source mu; f(r|m) is the PDF for distance to the earthquake rupture; P(Z z | m,r) is the probability that for a given magnitude m earthquake at a distance r from the site, the ground motion exceeds level z. National Institute of Geophysics, Geodesy and Geography Hazard analysis for high risk facility sites PROBABILISTIC AND DETERMINISTIC Detailed investigations at least in 25-30 km regions Logic tree approach Monte Carlo approach National Institute of Geophysics, Geodesy and Geography Hazard assessment for parts of Bulgarian territory Seismic hazard for the region of Sofia, 1000 years return period PGA (g) 43.0 0.45 42.9 42.8 0.40 SOFIA 42.7 0.35 42.6 0.30 42.5 0.25 42.4 42.3 0.20 22.6 22.8 23.0 23.2 23.4 23.6 23.8 24.0 National Institute of Geophysics, Geodesy and Geography COMPLEX GEOLOGO-GEOPHYSICAL AND SEISMOLOGICAL MAP National Institute of Geophysics, Geodesy and Geography National Institute of Geophysics, Geodesy and Geography Influence of intermediate Vrancea earthquakes National Institute of Geophysics, Geodesy and Geography DEAGGREGATION OF THE 475 YEARS HAZARD – Northern cities The city of Varna The city of Targovishte 0.14 0.25 0.12 0.2 0.1 4.5 4.5 0.08 5.0 0.15 5.0 5.5 5.5 0.06 6.0 6.0 6.5 0.1 6.5 0.04 7.0 7.0 7.5 7.5 0.05 0.02 Normalized number of exceedance 0 0 Normalized number of exceedances 340 320 300 300 280 280 260 260 240 240 220 220 200 200 180 180 160 160 140 7.5 7.5 140 120 7.0 7.0 120 100 Distance (km) 80 6.5 100 6.5 80 Distance (km) 6.0 60 6.0 60 5.5 40 5.5 40 5.0 20 0 5.0 20 4.5 0 M M 4.5 The city of Dobrich The city of Shumen 0.25 0.3 0.2 0.25 4.5 0.2 0.15 4.5 5.0 5.0 5.5 0.15 5.5 6.0 0.1 6.0 6.5 6.5 7.0 0.1 7.0 7.5 0.05 7.5 0.05 Normalized number of exceedance 0 0 Normalized exceedances number of 340 320 300 260 280 240 260 220 240 200 220 180 200 180 160 160 7.5 140 7.5 140 7.0 120 7.0 120 100 100 Distance (km) 6.5 80 6.5 80 60 6.0 60 6.0 Distance (km) 5.5 40 5.5 40 5.0 20 0 5.0 20 4.5 0 M M 4.5 DEAGGREGATION OF THE 475 YEARS HAZARD THE 475 OF DEAGGREGATION National Institute of Geophysics, Geodesy and of GeodesyGeographyInstituteGeophysics,National The city of Stara Zagora The city of Sliven 0.12 0.25 0.1 0.2 0.08 4.5 0.15 4.5 5.0 5.0 0.06 5.5 5.5 6.0 6.0 0.1 6.5 6.5 0.04 7.0 7.0 7.5 7.5 0.05 0.02 Normalized number of exceedance Normalized number of exceedances 0 0 360 360 340 340 320 320 300 300 280 280 260 260 240 240 220 220 200 200 180 180 160 160 140 140 7.5 7.5 120 120 7.0 7.0 Disrance (km) Distance (km) 100 100 80 80 6.5 6.5 60 60 6.0 6.0 40 40 5.5 5.5 20 20 0 5.0 0 5.0 4.5 M 4.5 M The city of Yambol The city of Burgas – 0.25 0.25 Southern cities Southern 0.2 0.2 4.5 0.15 4.5 0.15 5.0 5.0 5.5 5.5 6.0 0.1 6.0 0.1 6.5 6.5 7.0 7.0 7.5 7.5 0.05 0.05 Normalized number of exceedances Normalized number of exceedances 0 0 400 380 360 340 200 320 300 180 280 260 160 240 140 7.5 220 200 7.0 120 180 100 6.5 160 80 140 7.5 120 6.0 60 Distance (km) 7.0 100 80 6.5 5.5 40 Distance (km) 60 6.0 40 5.0 20 5.5 0 20 M 0 4.5 5.0 M 4.5 National Institute of Geophysics, Geodesy and Geography DEAGGREGATION OF THE 475 YEARS HAZARD – South-Eastern part South-East 475 г. 0.08 0.07 0.06 0.05 4.5 5.0 0.04 5.5 6.0 0.03 6.5 7.0 0.02 7.5 8.0 0.01 Normalized number of exceedances 0 480 440 400 360 320 280 240 200 160 8.0 120 Distance (km) 7.5 7.0 80 6.5 6.0 40 5.5 5.0 0 M 4.5 National Institute of Geophysics, Geodesy and Geography .