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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-21 20:58 |
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Conference: Bucharest University Faculty of Physics 2008 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
Attenuation relations for maximum acceleration produced by Romanian crustal and subcrustal earthquakes (POSTER)
Authors:
E. Popescu, A. Tugui, A.O. Placinta , I.A. Moldovan and M. Radulian
Affiliation:
INCDFP
E-mail
atugui@infp.ro
Keywords:
attenuation relation
Abstract:
A fundamental element for seismic hazard assessment is the variation of the ground motion amplitude depending on distance, magnitude and local soil conditions. Predicting the maximum acceleration values as a function of earthquake magnitude, hypocentral distance and source radiation using the attenuation relations represents an important goal in the field of seismic hazard as well. In order to apprehend and forecast the effects of strong and major Vrancea earthquakes we have obtained attenuation relations using a data set composed by the peak ground horizontal acceleration from 27 subcrustal and 17 crustal earthquakes recorded by the K2 strong motion array in Romania, array centered on Vrancea seismic region. The database consists of intermediate earthquakes of magnitudes and depths between 4.0 ≤ MW ≤ 6.0 /71 ≤ h ≤ 166 km, occurred from 1997 to 2004 and crustal events of magnitudes and depths between 2.6 ≤ MW ≤ 3.3 /3 ≤ h ≤ 38 km occurred from 2003 to 2007. The dependent parameter we have selected the peak ground horizontal acceleration (in time domain) as a measure of site intensity level. This value was corrected for the site effect in each recording station location, with the help of a multiple site factor, named S, and having different values, depending on the soil structure: 0.8 ≤ S ≤ 1 for hard soils, 0.7 ≤ S ≤ 0.8 for soft surface sedimentary soils and 0.65 ≤ S ≤ 0.7 for soft deep sedimentary soils. We have analyzed the attenuation relationships for moderate Vrancea subcrustal and crustal earthquakes, following a two step regression model, on two main directions (NE-SW and NW-SE) and two segments of depths, taking into account the division of the subducted litosphere beneath Vrancea zone. The Vrancea source induces a high seismic risk in the densely built zones of the South-East of Romania because the fundamental periods of the peak accelerations recorded at the large intermediate–depth shocks (1-1.5 s) are close to the natural periods of modern tall structures, contributing to severe damages of such structures. A number of 32 reinforced concrete multi-storey buildings completely collapsed during the shock that hit Bucharest on March 4, 1977. That’s why, predicting the ground motion acceleration during a major earthquake is of crucial importance for assessing more accurately the seismic hazard and for proposing hazard mitigation actions.
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