Site characterization of the strong motion stations and evaluation of site effects in the Ankara region during the December 2007 and March 2008 moderate Bala earthquakes

Local site conditions may significantly affect the amplitude and frequency of ground motion during earthquakes. Recordings of recent major earthquakes have demonstrated that soil conditions can generate prominent amplification of ground shaking and can be compared with the amplification predicted by numerical simulation. This study analyzes the ground motion data from the December 2007 and March 2008 moderate Bala earthquake series considering the effect of soil conditions on ground shaking in the southern part of Ankara, the capital city of Turkey. Initially, shear wave velocity profiles of the strong ground motion stations were evaluated to define site classifications for each station in Ankara and its surroundings. Strong motion data collected during the Bala earthquake series (M _w range 5.6–4.8) were used to develop event-specific attenuation relationships for peak ground acceleration and spectral acceleration at various periods and different site conditions. Site amplification factors were derived from the regression results from the event-specific attenuation relationships for the Bala earthquake series. The implications of these ground motion amplification factors were also discussed and compared using the current seismic design codes. Finally, the response spectra from the recording stations were used to determine site amplification factors for different site conditions to evaluate the variability of the site response in localized regions in Ankara.