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Ali Osman Öncel and Ömer Alptekin

Istanbul University, Department of Geophysical Engineering, 34850 Avcýlar-Istanbul/Turkiye.

Abstract. The spatial and temporal variations of earthquake occurrence in Turkey are investigated by using the Gutenberg-Richter b-value and the fractal (correlation) dimension (D_C) of earthquake epicenters. This investigation covered a period between 1900 and 1992 in the strike-slip fault zones “The North Anatolian Fault Zone (NAFZ), the East Anatolian Fault Zone (EAFZ), and the North East Anatolian Fault Zone (NEAFZ)” in Turkey for earthquakes of M³ 4.5. Also, the temporal variations of seismicity along the west (24°-31°E) and the central (31°-41°E) part of the NAFZ are determined from fractal analysis by using the b-value and the fractal dimension of earthquake epicenters. In the examination of spatial characteristics of strike-slip fault zones from the earthquake data, systematic spatial variations are found which may be related to structural or mechanical variability along the strike. In particular the large change in strike at the northern apex of the NAFZ is associated with the highest correlation dimension and the lowest b value for seismicity in this century. In the examination of the temporal characteristics of earthquake occurrence, a strong negative correlation (r=-0.85) for the central NAFZ (31°-41°E) and a weaker negative correlation (r=-0.56) for the western part of NAFZ (24°-31°E) is observed between b and D_C, consistent with previous observation of seismicity in Japan and Southern California. The low b and high D_C are respectively consistent with greater stress intensity and greater spatial clustering of epicenters-both implying a greater degree of stress concentration at this time.