LOCATION IMPROVEMENTS FOR THE TWIN CRUSTAL EARTHQUAKES RECORDED ON FEBRUARY 2023 IN GORJ COUNTY, ROMANIA

Abstract

A significant seismic sequence started on 13 Feb. 2023 at 14:58 GMT with a mainshock of 5.2 ML located at 17 km depth and at 14 km distance NW from Targu Jiu city. The first shock was followed by 16 aftershocks with magnitudes between 2.1 and 3.4 after which a second mainshock of magnitude 5.7 was triggered next day, 14 Feb., at 13:16 GMT. The largest acceleration at the second shock (105.25 cm/s2) was recorded at Gura Zlata station as well. The seismic events hypocenters are established by several methods. First two main shocks (with ML>5) are preliminary located using 10 seismic stations around the seismic zone. The second set of locations have as input data from seismic stations situated 100 km distance around the active area. The third set of locations are realized with all available Romanian seismic stations placed all over the country. The third locations of the main shocks performed routinely by the National Institute for Earth Physics (NIEP), Romania, placed the two main shocks several kilometers to the south and out from the cloud of aftershocks. As shown in our analysis, this is an artifact when different sets of stations are used in location procedure that can be explained based on the difference between the lithosphere models in different parts of Romania and the simplified model used by NIEP for routinely determination of events location with Antelope program.