DISTRIBUTION OF A AND b VALUES AND QUANTITATIVE SEISMICITY OF IRAN

The distribution of a and b values in the Gutenberg-Richter's formula is investigated for the seismic zones of Iran by analyzing close to ۴۰۰۰ events comprising the historical earthquakes and the lwentieth century shocks. In order to study the distribution of a and b values, a unit running window of ۲۰ square is set up and moved at an interval of ۰.۵ degree either in the longitudinal direction or in the latitudinal direction throughout the region. The method is meant to be new for the study of quantitative seismicity of the Iranian Plateau. Based on the distribution of a and b values of more than ۸۰۰ points, during the ۹۵ year period from the beginning of ۱۹۰۰ to the end of ۱۹۹۴, quantitative seismicity maps, the a-value map, and the b-valve map have been prepared and compared with the regional tectonics. Furthermore the a-value seismicity map reveals the same seismic pattern as that of the b-value map. The calculated a and b values are also listed and a straight-line least-squares fit is obtained for them, which gives a = ۵.۸۴b + ۰.۶۰ for various seismic zones of the Iranian Plateau. To our knowledge the formula is derived for the first time for Iran.