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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:10 |
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Conference: Bucharest University Faculty of Physics 2007 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
Local response in Bucharest urban area inferred from moderate-size Vrancea earthquakes
Authors:
B. Grecu, M. Radulian, A. Bala, N. Mandrescu, B. Zaharia
Affiliation:
National Institute for Earth Physics
E-mail
bgrecu@infp.ro
Keywords:
H/V ratios, peak ground motion, Bucharest urban area
Abstract:
The Bucharest metropolitan area is one of the most vulnerable urban areas in the world at the impact of the earthquakes generated in the Vrancea seismic source, at about 150 km epicentral distance. For example, the earthquake of 4 March 1977 (Mw = 7.4), occurred at 94 km depth, caused the collapse of 32 buildings of 8-12 storeys, while about 150 old buildings of 6 to 9-storeys were strongly damaged, many of them being subsequently demolished. The Vrancea seismic region is characterized by an unusual concentrated seismicity at intermediate depths (60-180 km), located beneath South-Eastern Carpathians, in Romania. Historical information over one thousand years suggests a rate of 2-3 damaging earthquakes per century. The studies done after the 1977 earthquake had shown the importance of the surface geological structure upon ground motion parameters. The Quaternary sedimentary deposits within the city of Bucharest consist of a succession of several lithological horizons: ‘Fratesti layers’, marl complex, ‘Mostistea sands’, intermediate clays, ‘Colentina gravel and sands’ and loesslike deposits. The entire complex undergoes a slight descend from south to north, accompanied by an increase of the deposits thickness in the same direction from about 150 m to 350 m. The purpose of our paper is to investigate the variability of the seismic ground motion due to local conditions within Bucharest area during moderate Vrancea intermediate depth earthquakes. We use in our study data from 14 Vrancea intermediate-depth earthquakes (M = 4.3 – 6.0) recorded by 13 digital accelerometers operated by National Institute for Earth Physics. The analysis is performed in both time (PGA, PGV) and spectral domains (H/V spectral ratios). Our results complement previous works and will be used in further microzonation assessment studies.
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