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Abstract:
The Vrancea Seismic Zone (VSZ), located in Romania, at the sharp bend of the South-East Carpathians, is an anomalous intra-plate seismic nest releasing the largest strain in continental Europe. The last powerful earthquake in Vrancea occurred in 1977 causing significant damage to the densely populated cities in South-East Romania. The seismic infrastructure was underdeveloped at that time and the earthquake was not well-recorded locally. Using ambient seismic noise recorded at modern broadband seismic stations around Vrancea in the year 2020, and the approximate moment tensor solutions of historical earthquakes Mw>6 since 1977, we reconstruct ground motion waveforms recorded by modern seismometers decades after their occurrence. The Virtual Earthquake Approach uses empirical Green's functions from ambient noise cross-correlations between pairs of seismic stations and adds the signatures of a model earthquake: double couple mechanism, buried source and a realistic earth model in the epicentral area. Ambient noise data capture the signatures of complex subsurface structures and the 3D path effects, providing a more physically accurate representation of the seismic wavefield than purely synthetic data. Our new results demonstrate the viability of this innovative method and provide a unique opportunity for more accurate seismic hazard analysis in intra-plate seismic zones with insufficient historical data.
