Application of Coda Q Method on Broad Band Recordings, from Local Earthquakes, in Albania

Interpretation of the high-frequency part in seismograms of local micro to moderate earthquakes can provide a wealth of information about the earth structure within a region.First to draw attention, to these continuous wave trains in the tail portion of seismograms, was Aki (1969). These waves appear immediately after the direct seismic phase arrivals and are termed “Coda”. The cause of their appearance is the superposition of the incoherent scattered phases from random heterogeneity within the Earth’s lithosphere (Aki, 1969, 1980; Aki and Chouet, 1975; Roecker W. S., et al, 1982; Chung, et al. 2009). It has been observed that the decay of coda wave amplitudes, of a local earthquake with time, can provide a quantitative estimate of the attenuation. The method based on this observation is widely referred to as Coda Q (QC). Aki and Chouet (1975) assumed coda waves to be single back-scattered S waves. Based on this model and using CodaQ routine in Seisan v. 1.9.1, (Havskov, et al., 2012) we have analyzed 55 earthquakes recoded by broadband seismological sensors of the Albanian Seismological Network (ASN). Dataset contains mainly local earthquakes and several regional ones. Taking into account vertical as well as horizontal components, secondary body waves S (Sg/Sn) are processed, which dominates expressing higher amplitudes. We determined parameters in the expression, , where in this frequency dependent model of the attenuation properties in the medium, express the quality factor determined for the characteristic frequency of 1 Hz, and α is the frequency term of the model (Dushi, 2011). The procedure description and results obtained are the subject of this paper.