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Mihaela Popa, National Institute for Earth Physics (Romania)
Mihaela Popa, National Institute for Earth Physics (Romania)
Mircea Radulian, National Institute for Earth Physics (Romania)
Neculai Mandrescu, National Institute for Earth Physics (Romania)
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The case of Vrancea seismic area, located at the sharp bend of the South-Eastern Carpathians in Romania, provides interesting features related to the seismicity behavior over several repeated seismic cycles. The data available for a millennium show an unusual concentrated and continuous seismicity at intermediate depths (60 ? 170 km), with 2 or 3 large events (M > 7) per century.
The Vrancea earthquakes are characterized by specific intensity patterns, with clear directivity in the spatial distribution and a huge extension, related to the entire South-Eastern Europe area. The goal of the study is to analyze the main properties characterizing the intensity distribution for Vrancea large and moderate earthquakes, using both macroseismic and instrumental information. To this aim we collected all the available data since 19th century to the present day. A major objective was to identify in the observed intensity patterns the properties related to the seismic source parameters (magnitude and focal depth) and to establish specific calibration relationships to evaluate these parameters.
The influence of the lateral inhomogeneities in the lithosphere and of the sedimentary cover in the study region upon the isoseismal or peak ground acceleration (velocity) patterns are considered as well in order to constrain the calibrations. Evaluation of focal depth and magnitude from historical data with acceptable uncertainty is of high significance for understanding the seismic cycle evolution and time-dependent seismic hazard assessment because these parameters seem to control specific features of the ground motion pattern in space and specific time sequences from one cycle to the other. Finally, using the new source parameters obtained from calibration, we tested the specific properties of the seismic cycle succession and integrate them in a geodynamic model for the study region.
Implications for major earthquake prognosis (expected magnitude, focal depth range and intermediate-term expectation of the occurrence in time) from one cycle to the other and the related seismic hazard are discussed as well.
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