Spatial variations of the fractal properties of seismicity in the Anatolian fault zones

Abstract

The Anatolian fault zones are seismically active strike-slip fault zones transcending the Anatolian plate in E-W and N-S directions. We investigate the spatial variations of seismicity along these zones in an attempt to investigate fault complexity along strike, quantified by the Gutenberg-Richter b-value and the fractal (correlation) dimension of earthquake epicentres, using the maximum likelihood method and the correlation integral, respectively. The investigation covers instrumentally recorded earthquakes of magnitude M > 4.5 occurring between 1900 and 1992. We find systematic spatial variations which may be related to structural or mechanical variability along strike. In particular the large change in strike at the northern apex of the North Anatolian Fault Zone is associated with the highest correlation dimension and lowest b-value for seismicity this century. The correlation dimension and b-value show a negative correlation with respect to each other, similar to results reported in other regional studies of Japan and southern California. This statistical correlation is stronger when more objective seismic zoning is carried out (based on number of events) rather than more subjective seismotectonic zoning in common use in seismic hazard analysis.