National Institute of Geophysics, Geodesy and Geography

Seismicity and seismic hazard modeling for 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 .

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 1901 – An earthquake with M=7.2 was realized in region. Maximal intensity X MSK. The earthquake caused heavy destructions along the sea side between the towns of 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, , -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 , 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

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 The city of

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 The city of

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 The city of

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