ANALYSIS OF FEATURE OF RECENT SEIZMICITY IN VLORA-ELBASANI-DIBRA SEISMOGENIC ZONE

The Vlora-Elbasani-Dibra transversal fault zone is one of the most interesting and specific tectonic of Albanides geological structure. Geotectonic processes developed through its, are connected and find the explanation of a number of local and regional geological phenomena. The Vlora-Elbasan-Dibra fault zone plays the role of a barrier against the regional pressure tension. This is why its southeast regions is much more structured than in the northwest territories. This transversal fault zone of ENE extension, which dislocates the Albanides along all their width is marked out by diapiric cupola of Dumrea, the Quaternary Depression of Elbasan, the belt of trasversal structure of Labinot which continue with the trasversal flysch elevation of Golloborda (fig 1). The results of the analysis, based on the parameters of events and some features of seismicity that have occurred in the Vlora-Elbasan-Diber seismogenic zone during period of time 2001-2014, are presented in this paper. The goal of this study is to determine tipology of seismicity, the source parameters of the mainshocks and their aftershocks in order to shed light on the seismotectonics of the area on the stress field. The data used in this study were recorded by permanent broadband seismological stations that are part of the Albanian Seismological Network as well by neighboring seismic networks NOA, MSO, INGV and MEDNET. The epicenters were located using P and S onsets, a local velocity model (Ormeni., 2011) and the Hypoinverse program (Klein, F.W., 2002). A complete and homogenous catalog of the earthquakes is provided. The focal mechanism solutions using the Focmec routine in the Seisan package (Haskov and Ottemoler., 2008). On the Vlora-Elbasan-Diber seismogenic zone during period of time 2001-2014 the microseismic activity was intensiv, occurred a alot of small earthquakes and two event with magnitude M=5.0. Focal depth analysis reveals that this seismicity was mainly generated in the upper und middle crust under the tectonic conditions described previously. We analysed and determined the focal mechanisms of 6 september 2009 (M5.4), of the 21May 2014 (M5.2), of the 16 Aprile 2007 (M4.5), of the 9 July 2010 (M4.6) and of the compound earthquakes of 24 October 2008 (M4.5), using first-onset polarities. Some aftershocks did not occur along the same fault plane as the mainshock; they occurred on faults with different orientations, reflecting the activation of secondary structures in the Elbasan-Dibra transverse fault zone and demonstrating a variety of geologic structures in the area with heterogenous stress state and the stress axes may often undergo rotations. The Vlora-Elbasan -Dibra fault zone has produced earthquakes in the past, and is expected to continue to be active in the future. The goal of this study is to determine tipology of seismicity, the source parameters of the mainshocks and their aftershocks in order to shed light on the seismotectonics of the area on the stress field.

Keywords:

Seismicity , Compound Earthquake , Gjorica Earthquake , Focal Mechanism.