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SOURCE PARAMETERS, CLUSTERING AND SCALING PROPERTIES FOR THE VRANCEA (ROMANIA) SUBCRUSTAL EARTHQUAKES RECORDED BETWEEN 2016 AND 2018
Abstract
The Vrancea zone, located in Romania, at the sharp bend of the Southeastern Carpathians, is a well-defined seismic region in a continental convergence area with unique properties and generating the most destructive subcrustal earthquakes in Europe. The seismicity is concentrated in a confined, high-velocity, focal volume at 60–200 km depth range. The increasing number and quality of waveforms digitally recorded in the last time by the National Institute for Earth Physics (NIEP) provide the opportunity to better constrain individual source properties and to systematically investigate collective scaling properties. These are fundamental elements to understand the overall seismogenic process in this particular geotectonic area. The purpose of the present paper is to investigate the source parameters and clustering properties for the moderate subcrustal earthquakes recorded between 2016 and 2018 using the Empirical Green’s function and spectral ratios techniques and to see how the results comply with the scaling laws characterizing the Vrancea subcrustal activity. In order to apply the relative deconvolution techniques, we selected a set of Green’s events, recorded between 2016 and 2018, in association with the main events, the largest earthquakes occurred in 2018 in the Vrancea intermediate-depth source: March 14, 2018 (Mw=4.2), April 25, 2018 (Mw=4.1) and October 28, 2018 (Mw=5.5). The application of relative deconvolution techniques shows 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 dimension resulted from our analysis on a set of 30 small and moderate earthquakes reproduces well (within inherent errors) the scaling obtained on larger data sets and the theoretical scaling generally adopted for simple source models.
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