HR: 0800h
AN: S51A-02    [Abstracts]
TI: Temporal variation of seismicity in the particular case of Vrancea (Romania) intermediate- depth earthquakes
AU: * Popa, M
EM: mircea@infp.ro
AF: National Institute for Earth Physics, 12 Calugareni str., P.O. Box MG-2, Bucharest-Magurele, 077125, Romania
AU: Rogozea, M
EM: mrogozea@infp.ro
AF: National Institute for Earth Physics, 12 Calugareni str., P.O. Box MG-2, Bucharest-Magurele, 077125, Romania
AU: Enescu, B
EM: benescu@eqh.dpri.kyoto-u.ac.jp
AF: Earthquake Hazards Division, Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan
AU: Radulian, M
EM: mircea@infp.ro
AF: National Institute for Earth Physics, 12 Calugareni str., P.O. Box MG-2, Bucharest-Magurele, 077125, Romania
AB: 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, between 60 and 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 (around 15 events/month with M greater than 3 and around 3 events/century with M greater than 7), the predominance of the focal mechanism, rise a lot of questions and debates in connection with this seismic area. We use a representative and homogeneous catalog of Vrancea intermediate-depth events recorded by the seismic network of National Institute for Earth Physics between 1994 and 2006 and a routine catalog for a 70-year time interval. 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). A JHD technique applied for hypocenters determination allows high accuracy locations and detailed and complex analyses related to seismicity evolution in time and space. We analyze the space and time variation of the seismic activity, frequency-magnitude distribution, fractal dimension, deformation accumulation curve (Benioff's curve), on different time and space windows and test any possible earthquake precursor. 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 particular configuration of the foci along NE-SW direction allows a 2D approach. 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. The largest events are the most infrequent, but the most important to understand, since they control the evolution of the system and are the most destructive events. Our detailed pattern analysis suggests that recognizable patterns of smaller, more frequent events can be used to detect the generation of the next major event although reliable and efficient forecasting of the largest events is still questionable. 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.
DE: 7200 SEISMOLOGY
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: 2007 Joint Assembly