Institute of Geophysics, University of Tehran, P.O. Box 14155-6466, Tehran, Iran
Determining seismic parameters especially estimating magnitude with enough precision has an important role in the explanation of the seismicity of a region. However, the method of magnitude determination based on an empirical relation, relates to the released energy in each earthquake. Magnitude scale is widely used because it is the proper method for estimating the size of the earthquake. In this study, to evaluate the reported magnitude value for Kojor-Baladeh earthquake which occurred on 28th May 2004, the value of magnitude was determined by using recorded seismograms in seismic stations then compared with that value reported by IGUT. The result of the investigation shows that the reported magnitude, about 0.6 magnitude unit was underestimated. This study shows that the main factor in this underestimation is the software which is used to process recorded data. Many researches have shown that it is better to estimate local magnitude by using measurements on horizontal components. This study also showed that in the Kojor-Baladeh earthquake the resultant horizontal amplitude of Lg wave on horizontal components is about twice the amplitude on vertical component.