Source parameters of the earthquake sequence that occurred close to the BURAR array (Romania) between 24 june and 1 july 2011

Abstract

The seismic activity in the Eastern Carpathians area is poorly recorded (a few hundreds of small-to-moderate earthquakes in the Romanian catalogue over the last century). The installation in 2002 of the high-performance Bucovina (BURAR) array in the Eastern Carpathians area contributed to a significant growth of the capacity to monitor local seismicity. As a consequence, the earthquake sequence occurred between 24 June and 1 July 2011 close to the BURAR array is the best seismic data set ever recorded for this area. The location of the events using all the available data provided by the real-time seismic network of the National Institute for Earth Physics suggests a NESW alignment along the western edge of the Avramesti-Suceava fault. This fault is crossing the Carpathian Foredeep underthrusting the foreland units to the orogeny area. The distribution of the first P-wave polarities is fitting the geometry of this fault, indicating predominant strike-slip faulting, with right-lateral movement. The compression axis oriented E-W is in agreement with the stress field characterizing the region. We applied spectral ratios and empirical Green’s function methods to estimate the source parameters (corner frequency, seismic moment, source duration, rise time) for the events with moment magnitudes higher than 2.5 belonging to this sequence. The results show a simple fracture model for the main shock of 24 June 2011 and an apparent constant stress drop scaling. Source parameter scaling relationships fit well the results obtained for other regions along the South-Eastern Carpathians and those which are typical for intra-continental areas.