Earthquake relocation for North-Western Greece using 3D crustal model; method comparison and seismotectonic interpretation.

Abstract

A dense microseismic network was installed in Northwestern Greece for a period of eleven months. A total of 1368 events were recorded and located using a 1D model. These events were also used to derive a 3D velocity model for the area. This work presents results from further processing of the data using (a) simple location method of events in a 1D medium through Hypo71 standard procedure; (b) location via the probabilistic, non-linear earthquake location method in 3D medium; (c) relocation of the events using the Double - Difference method in 1D medium; and (d) the same relocation procedure invoking 3D medium. The application of different location methodologies results in slightly different locations, which are evaluated using as criterion the compactness of hypocenter distribution. The three point method was used in order to derive linear characteristics from the hypocenter distribution and the final results were compared against the focal mechanisms of the events as computed using the polarity method and the 3D velocity model. The combination of accurately computed hypocenters and focal mechanisms provides important information for the seismotectonics of Epirus

S-Wave Spectral Analysis and Estimation of Spectral Parameters in Northwestern Greece

“…A dataset of 200 events was analysed using an S-wave spectral fitting technique and Brune model, to estimate seismic moment, stress drop, displacement and source radius. The initial dataset was divided in ten clusters according to seismotectonic characteristics of the area (Stavroulopoulou et al, 2013). Then, the regression analysis was applied to each cluster and to the whole dataset separately.…”

“…From this dataset, 200 well recorded events, which were relocated within the area of interest from Stavroulopoulou et al (2013), were selected and analysed in this paper. The duration magnitude of this subset ranges from 1.61 to 2.92 and the focal depth ranges from a few hundred meters to 35km.…”

“…The majority of focal depths were in the 0-10km range. In the same study of Stavroulopoulou et al (2013), the area was divided into ten clusters of events based on their spatial distribution. The spectrum analysis was applied per cluster, in order to correlate the estimated source parameters with the seismotectonic characteristics of each smaller structural area (cluster), extending the work of Stavroulopoulou et al (2013).…”

“…The focal mechanisms from earthquakes located in Epirus, denote thrust and strike slip to normal geological structures (Mercier et al, 1972;King et al, 1983;Doutsos et al, 1987;Underhill, 1989;Waters, 1994;Hatzfeld et al, 1995). Additional information derived from Martakis (2003), Tselentis et al (2006) and Stavroulopoulou et al (2013) seismotectonic studies in Epirus, agree with a thrust belt zone at the west, combined with an extensional regime at the eastern end.…”