STRESS FIELD IN TARGU JIU SEISMOTECTONIC AREA (ROMANIA): INSIGHTS FROM THE INVERSION OF EARTHQUAKE FOCAL MECHANISMS

Abstract

An intense seismic activity started in February 2023, close to Targu Jiu city, in the Oltenia region (Romania). The strongest events occurred on 13th and 14th February, the first shock with ML=5.2, and respectively the second shock with ML=5.7. These main shocks were followed by specific seismicity bursts (about 2000 foreshocks were registered). The focal depth of the events ranges from 1 to 20 km, most of them being situated in the 10-20 km depth interval. The area of interest is tectonically complex with various types of faults and it takes place at the contact between the Getic Depression, to the south, and the Southern Carpathians, to the north. The seismic sequence of Tg. Jiu occurred in the northern part of the Valea Motrului-Valea Oltetului area (part of Getic Depression) and is characterized by extensional faults, which show a general direction of ENE - WSW. For the seismic source delineated in Tg. Jiu area, the stress field has an extensional stress regime (?1 almost vertical), with maximum horizontal stress (SHmax) oriented in the NNE-SSW direction. The resulting SHmax orientation and normal fault regime with a radial component (R'=0.5) are consistent with the observed geological setting. The results of this study are useful for assessing past and current tectonic activities and future research of the epicentral area.