Scaling Properties for the Vrancea Subcrustal Earthquakes: An Overview

The Vrancea seismic nest is a distinctive case of unusually clustered seismicity at intermediate depths. The source scaling properties are essential elements to understand and model the tectonic processes responsible for generating earthquakes in such a confined lithospheric volume. The purpose of the present paper is to investigate the scaling laws for Vrancea earthquakes on the basis of well-defined source parameters. Spectral ratios technique and empirical Green's function deconvolution are applied to retrieve source parameters. Previous results are combined with new determinations resulting in an enlarged database (298 events), spanning a magnitude interval from M-w similar to 2.4 to M-w similar to 7.7 (1940 major event). The results show for the most of moderate-magnitude earthquakes a relatively simple source time function and source spectrum, compatible with a circular source model with homogeneous rupture process. The scaling of seismic moment with source radius and stress drop appears to be self-similar over the entire magnitude range of the considered data set (3.0 <= M-w <= 7.7) and matches well the theoretical scaling for source models generally adopted in source studies. Particular high stress drop values, for moderate and large events, indicate fast and efficient rupture processes at different scales, possibly explained by fast running shear melting processes.