Estimation of the Frequency-Dependent Shear Wave Attenuation from Acceleration Spectra of the Ahar-Varzeghan Earthquake 2012

Two destructive earthquakes occurred on the 11th of August 2012 in the regions of Ahar and Varzaghan, NW Iran. High-frequency strong-motion data of these earthquakes have been analyzed to determine the Qβ (f) and source parameters by inversion of the recorded data. The data from a local network of 21 acceleration records, for the first main shock and 19 records for the second main shock was used to estimate Q-relationship in 30 stations. The seismic hazard map for this region illustrates that most of the area in this province is located within high relative risk and characterized by a large number of heterogeneities. For frequency band of 1 to 20 HZ, the frequency-dependent attenuation for this region found to be Qβ = (94±29) f (0.82±0.05). The authenticity of achieved Qβ (f) relation is checked by comparing the source spectra in various stations with the theoretical spectra. Low values of the coefficient (Q < 200) in the Qβ (f) relation suggest that the region is seismically and tectonically active. The present inversion of strong-motion data gives the source parameters. The corner frequencies and stress drops are calculated as fc1= 0.08[HZ],fc2= 0.11[HZ], Δσ1=77.14[bar] and Δσ2=33.06[bar], respectively.