Study of Strong Ground Motion in the Bam Earthquake, Considering Uncertainty in Hazard Assessment

Despite the extensive efforts of seismologists and earthquake engineers to develop practical solutions for reducing earthquake-induced damage and enhancing the understanding of this phenomenon, many unknowns still remain. This lack of comprehensive knowledge results in significant uncertainties in calculations and measurements. Additionally, due to the multitude of parameters involved in engineering analyses, no precise modeling approach has yet been developed to accurately simulate and predict earthquake behavior. However, it is important to recognize that uncertainty in physical phenomena is not merely a matter of errors or mistakes but rather a fundamental principle. Given the critical role of strong ground motion estimation in human life, accurately determining the extent of uncertainty in our calculations is of great importance. The primary objective of this study is to examine the impact of uncertainties on seismic hazard analysis results. To achieve a practical and realistic comparison, the Bam earthquake of December 26, 2003, has been selected as a case study. Initially, various methods for estimating strong ground motion are briefly reviewed. This is followed by an introduction to uncertainties and an analysis of their influence on ground motion calculations. The study distinguishes between epistemic uncertainties, which arise from limitations in human knowledge and selected models, and aleatory uncertainties, which stem from the inherent randomness of earthquakes. The effect of these uncertainties on seismic hazard assessment results is analyzed based on different parameters. For any phenomenon to be understood and for computational results to be effectively applied, the accuracy of the findings must be well-defined. In complex phenomena involving multiple factors, errors in input parameters and prediction models introduce significant uncertainties in results. Each input parameter inherently carries uncertainties, which, when combined with knowledge-based uncertainties, contribute to a complex and incomplete understanding of the final results. Identifying the sources of uncertainties and their influence on outcomes allows for defining a range of possible results and determining the probability or confidence level of each. This process ensures a precise confidence margin for decision-making in design and analysis. Chapter 2 focuses on seismic hazard analysis, introducing different conventional methodologies. In Chapter 3, a general hazard assessment of Bam is conducted using deterministic and probabilistic methods based on pre-earthquake data, serving as a framework for comparative analysis in subsequent chapters. Chapter 4 explores uncertainty assessment using logic trees and fuzzy logic, discussing the implications of these methodologies. Chapter 5 presents the culmination of the study, summarizing findings and introducing two novel methods. The first method integrates logic trees and fuzzy logic into a "Fuzzy Logic Tree," leveraging computational efficiency for simultaneous application. The second method introduces an innovative approach to seismic hazard analysis by incorporating uncertainty in earthquake parameters through fuzzy logic linguistic variables. This "Simplified Linguistic Hazard Analysis Method" demonstrates promising results for seismic hazard assessment by incorporating expert opinions. Finally, the study includes relevant data, software codes, and an overview of Geographic Information Systems (GIS) in the appendices.

Study of Strong Ground Motion in the Bam Earthquake, Considering Uncertainty in Hazard Assessment Keywords:

Strong Ground Motion , Bam Earthquake , Seismic Hazard Assessment , Uncertainty , Earthquake Engineering