Modelling of the attenuation relationships from Western Anatolia strong motion data

In Western Anatolia region, which is one of the good examples of fast intracontinental extensional tectonic regimes, the need for seismic hazard studies has become progressively more important for earthquake engineering applications. Moderate sized earthquakes in the region are actually the dominant source of seismic hazard, because of their larger amplitude at longer periods in deep basin structures of Western Anatolia Graben System. For that reason, two-stage nonlinear regression analysis was applied to a database of the maximum horizontal component peak acceleration and 5%-damped spectral acceleration values of 202 recordings from 80 earthquakes, to predict ground motions by using empirical attenuation relationships for Western Anatolia. Moment magnitude range of the earthquakes, in the data set, is between 4.5 and 6.2 while the distance range is between 1 and 206 km. Predicted 5%-damped spectral acceleration values show that soil amplifications are significant for the basin geometry in the region. Comparison of obtained attenuation relationships with the relationships generated for tectonically different regions have shown that ground motion attenuation relationships in one specific region can not be simply modified for use in engineering analyses in another region. On the other hand, comparison of obtained attenuation relationships with the relationships generated for tectonically similar regions have shown that our model estimation is lower. This result is consistent with reported low velocities and high attenuation values of crustal structures in the region. Keywords: Attenuation relationship, nonlinear regression analysis, peak ground acceleration, response spectra, Western Anatolia, Turkey.