In order to investigate the seismicity of western Anatolia limited with the coordinates of 36°-40°N, 26°-32°E, Gutenberg-Richter magnitude-frequency relation, seismic risk and recurrence period have been computed. The data belonging to both the historical period before 1900 (I 0 ! 5.0 corresponding to M S ! 4.4) and the instrumental period until the end of 2006 (M S ! 4.0) has been used in the analysis. The study area has been divided into 13 sub-regions due to certain seismotectonic characteristics, plate tectonic models and geology of the region. All the computations have been performed for these sub-regions, separately. According to the results, a and b values in the computed magnitude-frequency relations are in the intervals 3.19±0.17 -5.15±0.52 and 0.42±0.05 -0.66±0.07, respectively. The highest b values have been determined for sub-regions 3 and 12 (Demirci-Gediz and Gökova Gulf-Mugla-Gölhisar). The lowest b values have also been determined for sub-regions 1 and 9 (Balıkesir and Bodrum-_ Istanköy). Finally, seismic risk and recurrence period computations from a and b values have shown as expected that sub-regions 1 and 9 which have the lowest b values and the highest risks and the shortestrecurrence periods.

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