One of the most important approaches in mitigation of casualties and damages of (especially huge) earthquakes is the rapid determination of earthquake parameters and among those, magnitude plays a key role. In this study, it was aimed to rapidly determine the earthquake magnitude by using continuous broadband data of the seismic network belonged to Ferdowsi University of Mashhad, Iran, and by taking advantage of the predominant period of P-wave. In terms of magnitude, the data ranges from 2.5 to 7 while considering epicentral distance, it is from 5 to 1600 km. During the computation of the predominant period, a period of transient will occur at the same time of onset detection of P-wave. To find the start and stop of this period, two techniques are introduced. By use of which, the ending limit will be found and after that, the maximum of computed period will be considered as the predominant period. The last step was to fit a model. Average error of different models was 0.8 that at its best, i.e., least available error along with the best available correlation properties (depending on the technique and sampling rate of the data), was able to determine the magnitude in less than 10 seconds (not for real-time use) and with the error of 0.6 of magnitude unit.

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