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Integrating the USGS National Seismic Hazard Model Into a Framework for Mapping Liquefaction-Targeted Ground Motions

Session: Recent Engineering Uses of National Seismic Hazard Models II

Type: Oral

Date: 4/22/2021

Presentation Time: 05:30 PM Pacific

Description: 

Current approaches for evaluating soil liquefaction potential in geotechnical engineering practice are largely based on simplified, cyclic stress procedures for estimating factors of safety against liquefaction (FS_L). Such procedures typically characterize cyclic loading imposed on soils using a combination of peak ground acceleration (PGA) and earthquake magnitude (M_w) that correspond to a single return period of ground shaking, as obtained from national or regional seismic hazard maps. Such an approach, which combines probabilistic seismic hazard analyses (PSHA) with deterministic liquefaction triggering calculations, does not completely represent the range of ground shaking conditions that can cause liquefaction at a given site; this limitation has been shown to lead to inconsistent applications of liquefaction hazard assessment across different geographic regions in the United States. Alternatively, fully probabilistic liquefaction hazard analyses (PLHA), which consider the full range of ground motions to estimate FS_L hazard curves, can be used to produce more consistent representations of liquefaction hazards than conventional methods. However, such analyses require voluminous calculations on data that is not widely available to practitioners. An alternative framework is therefore presented for using large-scale PLHA calculations, in conjunction with data from the USGS National Seismic Hazard Model (NSHM), to map a liquefaction-targeted peak acceleration parameter, PGA_L, that can be used in conventional liquefaction analyses to obtain FS_L estimates consistent with a target liquefaction return period. PGA_Lcan be mapped for a reference soil condition and target return period of FS_L throughout the United States, and factors for adjusting the PGA_L from reference to site-specific soil conditions are shown to be readily predictable from NSHM deaggregation data at a given location. The result is a framework that provides practitioners with revised ground motion parameters to accurately and consistently characterize liquefaction hazards across the U.S.

Presenting Author: Andrew J. Makdisi

Student Presenter: Yes

Authors