UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-22 2:36
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Conference: Bucharest University Faculty of Physics 2006 Meeting


Section: Atmosphere and Earth Science; Environment Protection


Title:
The estimation of the local response in Bucharest area using Nakamura method


Authors:
Bogdan Zaharia , Mircea Radulian , Mihaela Popa, Bogdan Grecu , Dragos Tataru


Affiliation:
National Institute for Earth Physics, 12 Calugareni St., 077125, PO Box MG-2 Magurele, Romania


E-mail


Keywords:
Nakamura method, microzonation


Abstract:
Bucharest is one of the most affected cities by earthquakes in Europe. Situated at 150 – 170 km distance from Vrancea epicentral zone, Bucharest has suffered many damages due to high energy Vrancea intermediate-depth earthquakes. For example, the 4 March 1977 event produced the collapse of 32 buildings with 8-12 levels, while more than 150 old buildings with 6-9 levels were seriously damaged. The studies done after this earthquake had shown the importance of the surface geological structure on ground motion. Bonjer et al. (1999) used for estimation of the local response the seismic noise recorded at 16 stations in Bucharest. The results showed that the spectral ratio obtained for the 16 sites are dominated by a clear resonance peak between 1 and 2 seconds, while their amplitudes remain constant around the value of 2. This study is a continuation of the Bonjer et al. (1999) study. For this purpose, we have used records of the seismic noise of 15 minutes length acquired in 2002 on 20 sites in Bucharest. The measurements were done with a K2 digital station equipped with a velocity sensor having the natural period of 5 seconds. For computation of the spectral ratios using Nakamura method (1989) the JSESAME software developed within the European project SESAME (http://sesame-fp5.obs.ujf-grenoble.fr) was used. The obtained ratios are dominated by a clear resonance in the period of 1- 2 seconds. The average period of these maxima is 1.43 s, while the average amplitude is 2.5. Our results confirm the previous ones and will be used in microzonation assessment studies.