Estimation of the kinematic source parameters and frequency dependent shear wave attenuation coefficient of the 18th June, 2007 Kahak-Qom earthquake in north central Iran

In this study, analysis is presented in two steps. in the first step, the theoretical s-wavedisplacement spectra, conditioned by frequency-independent q, was fitted with theobserved displacement spectra. therefore corner frequency, moment magnitude andfrequency-independent q for each record were estimated simultaneously and the estimateof error is given in the root-mean-square sense over all the frequencies. in the secondstep, the corrected observed displacement from source effect was fitted with path term ofbrune’s source model to estimate frequency dependent shear wave quality factor. forcomparison, frequency dependent shear wave quality factor also is estimated fromspectral decay method. the earthquake in qom, 18 june 2007 (ml=5.7), was the largestearthquake in the south of tehran that recorded on strong motion acceleration stations.the data represented more than 40 accelerograms recorded from kahak-qom earthquakein the hypocentral distance range from 18 to 170 km. the source term obtained frominversion was analyzed to estimate various source parameters. thereby, we estimatedseismic moment (1.86*1024 dyne-cm), corner frequency (0.72 hz ), source radius (2.33km), fault slip (38 cm), source duration (1.5 sec), stress drop (12.3 bars) and momentmagnitude (5.4), which are found to be consistent with the corresponding values reportedin published studies. the path average value of q is in the range q=161 to 1652. theanelastic attenuation coefficient for the region as a whole is estimated in step 2 is qs= 47f0.71 in frequency range of 1 to 32 hz. the frequency-independence attenuation for thestudy region shows that, in general, a q value is significantly similar to the entirefrequency range used than those found in other tectonic areas