The purpose of this study is to investigate the risk of earthquakes in the Urmia region by determining the parameters a and b of the Gutenberg-Richter magnitude-frequency relationship. For this purpose, based on the tectonic and seismographic data of the region, 4 different seismic springs were identified and zoned using geostatistical spatial analysis methods in the ARCGIS 10.3 environment. In this research, the value of b, which is the slope of the frequency-magnitude relationship of the Gutenberg-Richter relationship, was calculated using the maximum likelihood (ML) method. Also, I estimated the average return periods, the most probable maximum magnitude in the time interval of t years, and the probability of an earthquake with magnitude M => 7 in the time intervals of t years. Then we produced a map of the values ​​of the parameters a and b using the ML method. We obtained the lowest b value of 0.414 in seismic zone 1 and the highest value in zone 2 equal to 0.96 and zones 3 and 4 respectively 0.553 and 0.72. These results are strongly supported by the probability value (90 percent) that the largest earthquake with a magnitude greater than or equal to 6 on the Richter scale occurs in zones 3 and 4. We estimated the minimum return period of such an earthquake with the mentioned magnitude to be 79 and 169 years respectively in zones 3 and 4 of the region. We estimated the most probable earthquake with a magnitude of 6 and above in the next 100 years in 4 zones of the region, and the highest value of the earthquake magnitude scale was determined in zone 4 (M=7.7). Based on the parameters of the mentioned relationship and the type of tectonic regime of the region, zones 3 and 4, which mostly cover the southwest and north of the region, are the most dangerous zones in terms of seismic risks in Urmia region.

Keywords: Risk, seismicity, b value, Gutenberg-Richter, Urmia

     

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