Nr.2 - ALPA - Albanian Papers

Dushi & LameMATERIALS AND METHODA number of 55 earthquakes with localmagnitudes in the interval 2.3-5.5, recorded bySeismological Network of IGJE-o (Institute ofGeosciences) during 2008-2009 are used in thisanalyze, (Tab 1). Since 2003, ASN operates a VSATtelemetry network equipped with 7 BB sensors,(Fig 1).compose the later part of a local or regionalearthquake seismogram.Figure 2. Earthquake epicenter distributionFigure 1. Albanian Seismological NetworkFrequency response of these sensors is flat in thefrequency range 0.033Hz - 40 sec. Data weredigitized with 100 Hz sampling rate. Only eventswith minimum SNR are accepted and computedwith Seisan 8.1.2, (6). Earthquakes are locatedinside the area confined between 38.0-43.0N and19.0-21.0E (Fig 2), with focal depths between 0-70 km. Only seismic events recorded from morethan 2 seismological stations with RMS values inthe interval 0-1.3 sec, are considered. To performthis analyzes, Coda (Q) method is applied, as astandard spectral method (5). Coda wavesThe decay of these waves provides a quantitativeestimate for attenuation, widely referred to asCoda Q (Q C ). The decay of coda is due togeometrical spreading, intrinsic attenuation andscattering. These effects are connected toproperties of the medium and local geology. Asanomalies decrease with the depth inside theearth, less attenuation is observed and greatervalues of Q C are achieved. Coda spectrum ofsmall and moderate earthquakes depends onlyon the lapse time from origin. It has nodependence on the size of the event and pathcharacteristics due to an average scattering effectof the medium between hypocenter andrecording site. It was proposed a singlebackscattering model explaining coda assuperposition of secondary waves from randomlydistributed heterogeneities, (5). Coda amplitude,236AKTET Vol. IV, Nr 2, 2011