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Non-ergodic Probabilistic Fault-displacement Hazard Analysis

Description: 

The two main methods used for probabilistic fault-displacement hazard analysis (PFDHA) are the earthquake-based and displacement-based approaches. The earthquake-based approach is similar to ergodic probabilistic seismic hazard analysis used for ground motion, but the ground-motion model (GMM) is replaced by a global fault-displacement model FDM. In contrast, the displacement-based approach relies on empirical data of fault-specific displacement observations instead of using global FDMs, which is related to a non-ergodic approach. An issue is that the variability of the observed displacements at a site includes the effect of variability of the magnitude (M) and site distance from the end of the rupture (X) normalized by the rupture length (L) values. We do not know the M and X/L for paleoseismic displacement data, so we cannot directly compute the residuals as done for ground-motion data. To identify aleatory and epistemic components for the FDMs, we use the displacement hazard for generic source models to remove the effect of the M and X/L variability from the standard deviations of the observed slip at a point data sets. Using this formulation, we develop the first non-ergodic FDM, which results in a large reduction in the aleatory variability of displacement. Example PFDHA calculations using ergodic and non-ergodic approaches are shown for three cases: (1) without displacement data for the fault, (2) with displacement data at the site, and (3) with displacement data observed on the fault but a distance down strike from the site. With no data, the epistemic uncertainty is extremely large, but even a few data points provide significant constraints on the hazard with much narrower epistemic fractiles. Because the ergodic and non-ergodic approaches represent very different levels of simplification, the epistemic fractiles have different meanings for the two approaches. Therefore, the earthquake-based and displacement-based approaches should not be included as alternative branches on the logic tree.

Session: Temporally Variable Records of Earthquake Behavior and Considerations for Seismic Hazard Analyse [Poster]

Type: Poster

Date: 4/17/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Irene

Student Presenter: No

Invited Presentation: 

Poster Number: 37

Authors