Evaluating the Use of Multisite Probabilistic Seismic Hazard Analysis: A Case of Sarpol-e Zahab City, Iran

This paper evaluates the use of multisite (MS) probabilistic seismic hazard analysis (PSHA), which estimates the annual exceedance rate of a given level of ground motion in at least one of several sites as one of several possible results. For this purpose, (1) MS-PSHA is implemented through the Monte Carlo approach, taking into account various area sizes and correlation distances (CDs), and then (2) two proposals are represented as applications of MS-PSHA outcomes, both with reference to Sarpol-e Zahab City, a seismically active region located in the west of Iran. The first proposal attempts to determine the current code design probability of exceedance in at least one site, and the second one defines collapse prevention levels based on different probabilities of exceedance in at least one site. The efficiency of the results is discussed mainly by comparing them to recorded peak ground accelerations (PGAs) of three earthquakes, including the 2017 Sarpol-e Zahab 7.3 M event that largely exceeded the code design spectrum. MS-PSHA results demonstrate reasonable performance both in determining design ground motions and evaluating current design code when the exact seismic parameters of the study area are used in the analysis. Moreover, developed code-type design spectra based on MS-PSHA provided safety against collapse compared to a recently occurring low-probability event. MS estimates for various CDs and probabilities of exceedance in at least one site can also provide flexible design strategies regarding the importance of a structure and expected damage on a regional scale.