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 National Institute of Geophysics, Geodesy and Geography
DEAGGREGATION OF THE 475 YEARS HAZARD – Southern cities
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
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