DOI: 10.5593/SGEM2015/B13/S5.139


A. Bala, B.Grecu, C. Arion, D. Toma, E. Popescu
Friday 7 August 2015 by Libadmin2015

References: 15th International Multidisciplinary Scientific GeoConference SGEM 2015, www.sgem.org, SGEM2015 Conference Proceedings, ISBN 978-619-7105-33-9 / ISSN 1314-2704, June 18-24, 2015, Book1 Vol. 3, 1075-1082 pp

Different studies focused on the Vrancea subcrustal source of earthquakes pointed out the strong lateral inhomogeneous distribution of the seismic radiation. This implies characteristic macroseismic distributions, extremely elongated along NE-SW direction, and sharply restraint toward NW and SE. Many authors ascribed this particular radiation pattern to the predominant focal mechanism noticed for the major Vrancea shocks [1]. However, a few papers showed that the lateral variation in the subcrustal region seems to be more important (e.g., [2];[3]).
We plan in this paper to asses the importance of the source and path of the Vrancea earthquakes on the ground motion parameters in the area of Bucharest.
The fault plane solutions of most Vrancea earthquakes indicate a nearly pure thrust mechanism with the B-axis striking NE, which is typical for the strongest events. However there are some earthquakes that do not follow this pattern. We analyze the influence of focal mechanism radiation and source frequency content on the ground motion parameters in Bucharest area.
The role of the focal mechanism of the earthquakes and of the depth at which the earthquakes occur determine the path on which seismic waves are propagating to the surface. A significant role is played by the variation of the lithosphere structure between the depth of earthquakes (60 - 160 km) and the surface, for the seismic motion recorded in the Bucharest area.
The analysis of a recent set of intermediate depth earthquakes with Mw > 4.5, for which the focal mechanism have been computed, show the significant role played by the variation of these parameters in respect to the seismic motion recorded in the Bucharest area. These parameters might be in some cases as important as the site effects in establishing the local seismic hazard for the Bucharest City.

Keywords: source effects; site effects; wave path; earthquake magnitude; PGA variability.