Separation of source, site and near-surface attenuation effects in western Turkey

We analyzed 1764 records from 322 micro- and moderate-size local earthquakes in the central west Turkey to separate source, site and near-surface attenuation effects by utilizing a generalized inversion technique (GIT) to the spectra. GIT site transfer functions were compared with horizontal-to-vertical spectral ratio (HVSR) estimates by Akyol et al. (Pure Appl Geophys 170(12):2107-2125. doi: 10.1007/s00024-013-0661-2, 2013). Large amplitude values of vertical component GIT site transfer functions were obtained at different frequency bands for some of the sites. These results imply contaminations of HVSR estimates due to basin geometry induced waves caused by deep or shallow lateral heterogeneities. GIT source function estimates were interpreted as Brune source model. Weak epicentral dependence of near-surface attenuation parameter kappa with large scattering could be attributed to the source and propagation path complexities along different paths arriving to the stations. Large f (e) values with large kappa (0) values emphasize near-surface weathered zones attenuation effect at high frequencies.