The moderate-size earthquake (ML 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 M L ≥ 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-follows the orientation of the Vrancea crustal earthquakes alignment. The spatio-temporal distribution of the seismic activity, as well as the seismic energy release during the seismic sequence are analysed in detail, and the focal mechanisms of the largest events-34 shocks with local magnitude ≥ 1.8-are determined using reliable P-wave polarities and amplitude ratios. Taking into consideration that the moderate-size shock on 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.

Providing warning notification several seconds before dangerous earthquake waves arrive at a target site reduces the property damages and human casualties. Most earthquake early warning systems (EEWS) developed are either regional ("network based") or on-site ("stand alone") systems. The recent upgrade of the seismic network in Romania with high dynamic range accelerometers allows recording of moderate to large magnitude earthquakes at very close epicentral distances (less than 10-20 km). This allows an increase of the warning lead-time (the time difference between the alert notification time and the arrival time of potentially destructive waves at a given target). The seismicity of Romania is significantly affected by earthquakes produced by the Vrancea seismic source with intermediate depth events (three shocks/century with magnitude Mw greater than 7.0). In this paper we present the performance of the seismic network in rapidly locate events occurring in the Vrancea area. Since rapid location of earthquakes is the first step in issuing early warning notifications, by reducing the time of the first valid location will lead to an increase the lead-time interval. Also rapid location of events will allow a future upgrade of EEWS to cover the entire Romanian territory.

An unusual seismic swarm started on September 23, 2013, close to Galati city, in Izvoarele region (Romania), and lasted until November 12, 2013. 406 earthquakes were recorded during several phases of seismic activity. The strongest events-a magnitude 3.9 earthquake, occurred on September 29, and two M L 3.8 shocks, occurred on October 3 and 4, respectively, were accompanied by specific seismicity bursts. The seismogenic region of the swarm is situated between two main crustal faults, which builds up the primary fault system, oriented SE-NW: New Trotus Fault (at the limit between North Dobrogea and Scythian Platform) to the North and east, and Peceneaga Camena fault (which separates North Dobrogea block from the Moesian Platform) to the South. The epicentral zone belongs to a complex tectonic area, in which a secondary fault system-lying NE-SW, perpendicular to the primary system-is also present. The focal mechanisms show normal faulting, with an important strike-slip component, one of the nodal planes being oriented roughly in a NE-SW direction. The objective of this study is to investigate the seismic swarm recorded in a new seismic area of Romania, near the town Galati in Izvoarele region. We show detailed hypocentral location, focal mechanisms and the correlation between seismicity and tectonic structures.

<p>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<sub>L </sub>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 (<strong>σ1 </strong>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.</p> <p>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.</p> <p>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.</p>

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