Estimation of the Frequency-Dependent Shear Wave Attenuation from Acceleration Spectra of the Ahar-Varzeghan Earthquake ۲۰۱۲

Two destructive earthquakes occurred on the ۱۱th of August ۲۰۱۲ 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 ۲۱ acceleration records, for the first main shock and ۱۹ records for the second main shock was used to estimate Q-relationship in ۳۰ 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 ۱ to ۲۰ HZ, the frequency-dependent attenuation for this region found to be Qβ = (۹۴±۲۹) f (۰.۸۲±۰.۰۵). 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 < ۲۰۰) 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 fc۱= ۰.۰۸[HZ],fc۲= ۰.۱۱[HZ], Δσ۱=۷۷.۱۴[bar] and Δσ۲=۳۳.۰۶[bar], respectively. 

کلیدواژه ها:

Ahar-Varzeghan Earthquakes ، Strong Motion Data ، Source Parameters ، Shear wave attenuation