Source characteristics of the seismic sequences in the Eastern Carpathians foredeep region (Romania)

Abstract

The source parameters and scaling properties for two seismic areas (Vrâncioaia and Râmnicu Sărat) of the Carpathians Mountains foredeep, adjacent to the Vrancea seismic region, are analyzed by standard time and frequency domain methods and empirical Green's function deconvolution. The study area is characterized by distinct shallow seismicity clusters with small and moderate-size earthquakes ( M<5). The digital short-period and broad-band waveforms recorded by the Romanian seismic network are considered. The analysis of the retrieved source parameters possibly outlines a heterogeneous faulting process. A significant difference in the stress drop value is emphasized between Vrâncioaia and Râmnicu Sărat earthquakes, which is assumed to be ascribed to differences in the local seismotectonics and reology. Our paper shows the efficiency of the empirical Green's function deconvolution in eliminating the instrument, path and site effects for the earthquake sequences in the Râmnicu Sărat region. The apparent source time function is generally well constrained, as demonstrated by our tests using in parallel both, appropriate Green's functions of different sizes, and instruments with different frequency bandwidth.