Abstract
High-frequency strong-motion data of two recent major earthquakes in the Ahar-Varzaghan region, Northwestern Iran, have been used to determine shear-wave quality factor ( Q β ( f )) and seismic source parameters. Data from a local array of 12 stations, two main shocks (Ahar-Varzaghan doublet earthquakes ( M w 6.4 and 6.3) on August 11, 2012), and 38 aftershocks of magnitude 4.1 – 5 were analyzed. The classic Brune model is used to predict the shape of the source spectrum and to provide scaling relationships between spectral and source parameters. In order to obtain reliable estimates of the source spectrum, the effects of attenuation need to be estimated and corrected. By using an inversion algorithm in this work, an average relation in the form Q β = (114 ± 21) f (0.90 ± 0.07) is obtained. The best fit theoretical spectrum provides final values of source parameters, i.e. seismic moment M o and corner frequency f c as 3.19 × 10 25 dyne cm and 0.69 Hz, respectively, for the first event. Obtained Q(f) relationship suggests a low Q o value ( 0.8) for high heterogeneous, tectonically and seismically active regions.
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