Stress field in NW Galati seismotectonic area (Romania): insights from the inversion of earthquake focal mechanisms

An intense and unusually seismic activity, occurred during September-October 2013, in Galati-Izvoarele region, situated in the central-eastern part of Romania, between two main crustal faults, Sf. Gheorghe and Peceneaga Camena fault. With several hundred (~400) earthquakes recorded in a short time, the activity was considered as seismic swarm. The magnitude M_L was always below 4, with three shocks of magnitude 3.9, accompanied by specific seismicity bursts and focal depths ranging from 1 and 40 km. The focal mechanism solutions of the studied earthquakes obtained from P-wave polarities generally show normal faulting, with an important strike-slip component in several cases. For the seismic source delineated in Galati-Izvoarele area, the stress field has an extensional stress regime (σ1 almost vertical), with maximum horizontal stress (SHmax) oriented in the NNW-SSE 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 revealing the crustal stress field, and, as such, for assessing past and current tectonic activities and potential future earthquake generation.

Also, transdisciplinary studies can trigger unexpected collaborations between researchers from diverse fields to understand the processes and conditions causing the initial stages of rock failure, and the interplay between mineral and tectonic scale processes.