Seismic noise represents small amplitude ground motions that are recorded everywhere on the surface of the Earth and are generated by anthropic and natural factors such as traffic, industrial facilities, wind, oceanic and coastal waves, etc. Since the noise measurements can be performed anytime and everywhere, the importance of seismic noise data in seismology has significantly increased in the last twenty years. Thus, the use of noise data became very important for site effects estimation, investigation of shallow and deep structure of the Earth, understanding of processes as atmosphere-ocean-seafloor coupling (Rhie and Romanowicz, 2004) or climate changes (Stutzmann et al., 2009), seismic networks operation and more recently, for studying the changes in the medium velocity or evidence temporal physical changes in fault zones (Wegler and Sens-Schönfelder, 2007; Berenguier, et al., 2008).
The REASoN project focuses mainly on improving the knowledge of the nature and origin of the ambient seismic noise wavefield recorded on the Romanian territory. Continuous data recorded by four seismic arrays (Plostina-PLOR and Bucovina-BURAR arrays are part of the Romanian Seismic Network, while the other two are part of two temporary networks that were installed in Bucharest area - URrban Seismology network - and in the western part of Romania - South Carpathian Project network) and 14 stations belonging to the Romanian Seismic Network (Figure 1) will be used within the project in order to understand the variations observed in seismic noise and how these variations could affect the detection capabilities of seismic networks, the H/V ratios computed in urban environments or the dispersion curves obtained through cross correlations of ambient seismic noise. The project also adresses a new challenge for the seismic monitoring studies in Romania, i.e. the use of ambient seismic noise to monitor an active seismic area where, very recently, two seismic sequences occurred and caused some minor damages and frightened the people living inside the area: the swarm in 2013 from the Galati area with the main shock of magnitude 3.9 and more than 300 aftershocks (blue dots in Figure 1), and the seismic sequence in 2014 close to Focsani area with the main shock of magnitude 5.7 and more than 80 aftershocks (red dots in Figure 1).
Figure 1. Distribution of seismic stations and the target area for noise monitoring