A Reliable Method for Determining the Tapered Minimum Magnitude in a Probabilistic Seismic Hazard Analysis

Document Type : Original Research Article


Department of Civil Engineering, Engineering faculty, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran


One of the inputs of probabilistic seismic hazard analysis (PSHA) is the minimum magnitude (mmin) of damaging earthquakes. Recent studies have shown that the choice of mmin can affect the results of PSHA. That is, if the mmin value is low, the PSHA will be overestimated. Therefore, it is important to choose the mmin value in such a way that earthquakes with greater magnitude than mmin have the capability to damage the structure. Obviously, the mmin depends on the characteristics of the structure and the earthquake. The mechanism of occurrence of earthquakes in each region is such that earthquakes with different characteristics can occur. Therefore, earthquakes with the same magnitude cause different levels of damage to the structure. This paper uses a tapered line instead of the cut-off magnitude for mmin. In this regard, we model The 3, 5, and 8-story intermediate concrete frame using Opensees software and perform time history dynamic analysis based on 246 earthquake accelerograms. The structural damage is assumed based on the drift ratio. The drift ratio of 0.004 is assumed as the limit state for the operational performance (OP) level. Using the non-uniform distance number, the mmin taper line is obtained as [4.5, 5.5]. This number can be used as the integral lower bound in the PSHA.


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