The source mechanism of the seismic events during the sequence of the moderate-size crustal earthquake of November 22, 2014 of Vrancea region (Romania)

Abstract

The moderate-size earthquake (local magnitude 5.7) which occurred on November 22, 2014 in Vrancea region (Romania), is the largest crustal event instrumentally recorded.

Its aftershock sequence lasted around 70 days, 222 earthquakes with local magnitude ≥ 0.1 being located using the records collected by the Romanian seismic network.

The seismic sequence occurred mainly in the lower crust (depths greater than 25 km), and the epicenter distribution – along a NNE-SSW direction followed the orientation of the Vrancea crustal earthquakes alignment.

The sequence, occurred in the Focsani Basin (part of the Moesian Platform) and is related to the normal fault system associated to the major Peceneaga - Camena fault, which separates the Moesian Platform from the North Dobrogea promontory.

The spatio-temporal distribution of the seismic activity, as well as the seismic energy released during the seismic sequence are analysed in detail, and the focal mechanisms of the largest events – 34 shocks with M_L ≥ 1.8 – are determined using reliable P-wave polarities and amplitude ratios.

Taking into consideration that the moderate-size shock of November 22, 2014 is the strongest instrumentally recorded crustal earthquake in the region, its focal mechanism provides highly relevant seismological information on the deformation field in front of the Carpathian bend. The obtained fault plane solution indicates normal faulting with a dominant dip-slip component; both nodal planes being oriented NW-SE.