Quantifying Seismicity Parameter Uncertainties and Their Effects on Probabilistic Seismic Hazard Analysis: A Case Study of Iran

Probabilistic seismic hazard analysis (PSHA) can accommodate various sources of uncertainties and it provides a rational framework for the precise portrayal of the hazard of a given region. Often, the information used in the PSHA is incomplete and uncertain; therefore, the question arises how the uncertainty of the input data affects the estimated hazard characteristics. In this study, sensitivity analysis (SA) was conducted to identify the most dominant inputs affecting the assessment of the key seismicity parameters (SPs), including the mean seismic activity rate λ, b value of Gutenberg–Richter, and the maximum possible earthquake magnitude mmax\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$m_{ \hbox{max} }$$\end{document}. The study was applied in five areas of Iran, for which such analyses have not been conducted in previous studies. Subsequently, Monte Carlo simulation was employed to determine the effects of the uncertain input parameters on PSHA relevant to spectral accelerations corresponding to 10% and 2% probability of exceedance at least once in 50 years. For this purpose, a unified and declustered earthquake catalogue was used for the five major seismotectonic provinces of Iran (Alborz-Azarbayejan, Zagros, Central-East Iran, Koppeh Dagh, and Makran). The results showed that the last (complete) part of the catalogue has a significant effect on the estimated value of seismic activity and the b value. In contrast, its influence is insignificant on the area-characteristic maximum possible earthquake magnitude, for which the most influential inputs are the maximum observed earthquake and its uncertainty. Furthermore, the uncertainties of the input SPs affected the seismic hazard estimates substantially and led to significant variability in the estimated ground motion characteristics.