| Popis: |
Near surface attenuation parameter kappa (kappa) of S-waves is calculated from 52 earthquake acceleration recordings at surface and base level (V-s > 760 m/s, namely engineering bedrock) of three downhole arrays and at two outcrop stations in Istanbul, Turkey. Path dependent (kappa(R)) and site dependent (kappa(0)) components of kappa are calculated from epicentral distance (R-epi)- kappa correlations. Estimated kappa(0) values are for the outcrop stations are in the range of 26-30 ms, while for the surface and base levels of the arrays are 40-53 ms and 18-23 ms, respectively. A strong correlation is observed between relative amplification factors of downholes and kappa(0) differences between surface-base levels. On the other hand, kappa(0) not approaching to zero at base stations suggests that several other factors still contribute to other than path and site effects. Given the earthquake scenario and stochastic simulation approach, 10 ms decrease in kappa(0) is found to increase response spectral acceleration up to 0.2 g in 0.1-0.2 s structural periods. |
