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Issues in the Selection of Design Values for Surface Fault Rupture for Critical Facilities Using Probabilistic Fault Displacement Hazard Analysis

Description: 

For most applications, the approach to fault displacement hazard is avoidance through use of setbacks from active faults; however, for some lifelines, an active fault must be crossed. In other cases, new faults are discovered at existing critical infrastructure that need to be addressed. Historically, deterministic approaches have been used to estimate design fault displacement, but probabilistic fault displacement hazard analysis (PFDHA) is being used more frequently. The PFDHA follows a similar approach as standard probabilistic seismic hazard analysis (PSHA) used for ground motion, but there are issues that affect PFDHA that are not common in PSHA. The first issue is the selection of the design fault displacement based on the hazard curve. Often, the return period for the fault displacement is simply set at the same return period as the ground motion for the structure; however, the objective should be to have similar risk for fault displacement and ground motion, not similar hazard. Because the fault displacement hazard only includes events that rupture to the surface at the site, the hazard curves are flat at small displacements. If the recurrence interval for surface rupturing events at the site is not much larger than the selected return period, then the displacement at a given return period will be sensitive to the uncertainty in the activity rate. For example, an increase in the slip rate of a factor of 2 can lead to a factor of 6 increase in the displacement at the specified rerturn period. If a risk-targeted displacement is developed based on the same risk level used for buildings, the displacement can be a factor of 3 larger than the displacement for the 2500-yr return period. In many cases, simply using the displacement based on the mean hazard for a specified return period will not be appropriate for the design of critical infrastructure. GIven the sensitivity of the PFDHA results, alternative approaches to selecting the design displacement should be considered, such as using the median displacement from the distribution of displacements for events causing surface rupture at the site.

Session: Assessing Seismic Hazard for Critical Facilities and Infrastructure – Insights and Challenges - II

Type: Oral

Date: 5/3/2024

Presentation Time: 04:30 PM (local time)

Presenting Author: Norman

Student Presenter: No

Invited Presentation: Yes

Authors