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The Role of Epistemic Uncertainty Estimations in Seismic Safety Decision Making and Relation to Levels of Input Model Simplification

Description: 

Epistemic uncertainty and aleatory variability are key concepts in probabilistic seismic hazard analysis (PSHA). The classifiation into either epistemic or aleatory depends on the level of simplificatoin used in the seismic source characterization and in the ground-motion model. For a selected level of simplification, epistemic uncertainty is scientific uncertainty in the modeled earthquake effects while aleatory variability is the variability from unmodeled earthquake effects. Models with greater simplification will have larger aleatory variability and smaller epistemic uncertainty than models with less simplification. Although common PSHA practice is focused on the mean hazard, which is not affected by the partitioning of epistemic uncertainty and aleatory variability, the evaluation and quantification of the epistemic uncertainty is often required for seismic hazard studies for critical infrastructure projects. Therefore, the level of model simplification should be clearly defined in the PSHA to allow the users to be able to interpret what the epistemic uncertainty range represents. A common assumption is that the true hazard will lie within the epistemic uncertainty range; however, we show that this will generally not be the case for models with greater simplification and larger aleatory variability, such as ergodic GMMs. The most common use of epistemic uncertainty is to identify the key inputs that can be improved and reduced through additional data collection and improvement. Less discussed are the potential uses of epistemic uncertainty in engineering practice. Though regulations and codes typically specify that the mean hazard be used for determining the design ground motions, the performance of the structure can be evaluated to higher fractiles of the hazard. To help meet societal needs for earthquake resilience, the damage state of the structure can be considered in the development of emergency action plans to respond to the expected consequences if the ground motions for the higher fractiles are correct.

Session: Assessing Seismic Hazard for Critical Facilities and Infrastructure – Insights and Challenges [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Irene

Student Presenter: Yes

Invited Presentation: 

Authors