A new attenuation relation for peak ground acceleration (PGA) in the Marmara region of northwestern Turkey has been developed. The data base consists of 751 horizontal components of peak ground acceleration recorded from 78 earthquakes, including the 1999 Izmit (Mw = 7.4) and the 1999 Duzce (Mw = 7.2) earthquakes. All the raw records are of the main earthquakes and their aftershocks. Baseline and instrument corrections have been applied to these raw records. Fast Fourier Transforms (FFT) have been calculated for all the records to select the high-pass and low-pass filters after these corrections. Multiple regression analyses have been used to calculate the relationship. The proposed attenuation relationship is

logA = −2.7809 + 0.5344 Mw − log(rrup + 0.0183 x 10^(0.4537 Mw)) − 0.0015 rrup

where A is the peak ground horizontal acceleration in g, Mw is the moment magnitude and rrup is the closest distance from the surface projection of the rupture area. If the Mw magnitude and the fault plane solution are not defined for an event, then other magnitudes are converted to Mw magnitude using a correlation formula. The peak ground horizontal acceleration attenuation relationship has been found to be log-normally distributed with a standard error representing a 0.392 percent increase in terms of natural logarithm.