Strong earthquakes in the Vrancea region occur between 70 and 180 km depth within an almost vertical column. Depth and estimated moment magnitude Mw (proportional to released elastic energy) of all instrumentally recorded evens are summarized as follows: 0-40 km, Mw <5.5 and moderate seismic activity; 40-60 km, no seismic activity and low velocities; 70-90 km, May 30,1900 earthquake with Mw =6.9; 90-110 km, March 4,1977 earthquake with Mw =7.5; between 110 km and 130 km, not ruptured since 1802, October 26 (Mw =8.00 the strongest earthquake in this part of Central Europe); 130-50 km, August 30,1986 with Mw =7.2; 130-180 km, November 10,1940 earthquake with Mw =7.7; 180-200 km, no seismic activity and at 220 km depth-deepest event ever recorded with Mw =3.7. From these data, the ruptured areas migrated from 150-180 km (1940) to 90-110 km (1977) to 130-150 km (1986) and to 70-90 km (1990) depth. The depth interval between 110 and 130 km remained unruptured since at least 200 years. This depth interval is a natural candidate for the next strong Vrancea event. The ground shaking during the 1802 Vrancea earthquake caused faults in the alluviated sand, and black oil areas in Bucharest (in the SE part of Bucharest there are 2 layers of coal) and mud were ejected. This phenomenon did not happen during March 4, 1977 Vrancea earthquake (Mw =7.5).
The earthquake on November 10, 1940 (Mw=7.7) and a focal depth of 150 km caused considerable havoc in East and South towns of the mountains. On the evening of March 4,1977, magnitude Mw =7.5 earthquake rumbled up from deep seismic region under Vrancea (depth 93 km) and shook a wide part of Eastern Europe. The highest intensities were in the South of Carpathians, in Romania, heavily damaged part of Bucharest, Ploieşti, Zimnicea, Russe (Bulgaria) and other Romanian and Bulgarian towns, but earthquake was felt as far as Moscow and Roma (Figure 3)[24]. Damages were reported along Danube in Yugoslavia and Bulgaria. The 4 March 1977 earthquake has produced heavy social ad economic effects. According to official data 1,574 victims have been identified (some 90% of them in Bucharest, at a distance of about 160 km SSW from the foreshock epicentre and about 100 km S from the main shock epicentre). More than 11,300 persons have been injured. 32,900 dwellings have collapsed or have been badly damaged and 35,000 families have lost their shelter[18]. Many schools and hospitals have been damaged. Many industrial enterprises have been affected also and important production losses have been recorded. It was the strongest earthquake to take place in Central Europe in modern times. More, in Bulgaria, the wave field radiated by Vrancea intermediate depth earthquakes mainly at long periods (T>1.2 seconds) attenuates with distance less rapidly than the wave field of the earthquakes in other seismically active zones in the country. Therefore, large industrial areas can be seriously damaged by strong events originating in this seismogenic area. In fact, even if the Vrancea 1977 event motivated some changes in the Bulgarian Code for design and Construction in Seismic Regions’87, the seismic excitation from the 1986 and 1900 events exceeded the seismic loading prescribed in the BG Code’87. The Vrancea intermediate depth earthquakes have been felt with macroseismic intensities up to I=VIII (MSK-64) at Bucharest and I=VIII (MSK 64) at Russe, Bulgaria.
Am copiat aici selectiuni dintr-un document pdf. Dodo nu deschide pdf-uri, asa ca am postat aici textul. E in engleza, dar cred ca se intelege destul de bine ideea...:ack::wink::hypocrite::wink: