Role of Uncertainties in Site Response Analysis and Their Incorporation in Seismic Hazard Workflow

Abstract

The inherent randomness in the underlying geotechnical and geological formations makes its characterisation highly site-specific. While mapping the hazard at a larger scale, the site characteristics sampled at individual locations are collectively used to represent an entire region. Maps representing local geology, soil amplification, and hazard of a region are created through spatial interpolation of the site-specific estimates. Since the half-space is highly unpredictable, the estimates are probabilistic with a certain amount of uncertainty. This uncertainty can be partly modelled during the computation of site response while a fraction of it will remain as a standard error or deviation of the estimated values. The latter is known as aleatory uncertainty while the former is known as epistemic uncertainty. When the uncertainties are systematically partitioned and accounted for in the hazard integral, an ergodic approach (conventional PSHA with no site-specific information) transforms to a non-ergodic (completely site-specific) and partially non-ergodic approach (partially site-specific). The present article outlines the scope of a non-ergodic PSHA in the Indian scenario and the existing practices in capturing the uncertainties introduced by the site component. The authors believe that the article can provide insight towards improving the existing site-specific PSHA practices in the country. © 2023, Indian Society of Earthquake Technology.