UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2007 Meeting


Section: Atmosphere and Earth Science; Environment Protection


Title:
Seismicity characteristics of the Vrancea (Romania) intermediate-depth earthquakes


Authors:
Maria Rogozea1, Bogdan Enescu2, Bazacliu Olivia1, Mihaela Popa1, Mircea Radulian1


Affiliation:
1) National Institute for Earth Physics, P.O. Box MG-2, 077125, Bucharest-Magurele, Romania

Tel.: +4021 493 01 17, Fax: +4021 493 00 53

2) Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto

University, Gokasho, Uji, Kyoto 611-0011, Japan


E-mail
mrogozea@infp.ro


Keywords:
seismicity, Vrancea


Abstract:
The aim of the study is to investigate the temporal behavior of some common seismicity parameters and define seismicity pattern for the Vrancea seismogenic zone, located at the South-Eastern Carpathians arc bend, in Romania. A persistent and unusually strong cluster of earthquakes is generated here in a confined volume at intermediate depths (60 – 180 km). The atypical geometrical configuration of the hypocenters, elongated along NE-SW direction and close to a planar distribution, the persistence of the earthquake generation in time, rise a lot of questions and debates in connection with this seismic area. The seismicity are investigated on the basis of a set of Vrancea intermediate-depth events recorded by the seismic network of National Institute for Earth Physics between January 1995 and April 2007. The refined catalog is complete for duration magnitudes above 3 and contains only small and moderate earthquakes (Mw 5.8 was the largest observed magnitude). We analyze the space and time variation of the seismic activity, frequency-magnitude distribution, deformation accumulation curve (Benioff’s curve). The study area, situated between 60 and 180 km depth, is divided in two active segments, one centered around 90 km depth, other centered around 140 km depth. The evolution of seismic activity shows alternative accelerating and decelerating deformation release in the upper segment and lower segment, respectively, of the subducting lithosphere. The different seismicity behavior in the two segments of the seismic active volume and the apparent interconnection between them can be speculated to predict the most probable future particular seismic hazard pattern. We identify the characteristics of the preparation process of the strong subcrustal events originating in Vrancea region and analyze how they can be incorporated in a time-dependent seismic hazard assessment.