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SCEC2021 Plenary Talk, Earthquake Engineering Implementation Interface (EEII)

Spatial distributions of liquefaction for seismic risk analysis

Jonathan P. Stewart

Oral Presentation

2021 SCEC Annual Meeting, SCEC Contribution #11221
Seismic risk for spatially distributed infrastructure is driven mainly by ground failure, defined as permanent ground displacements from mechanisms such as liquefaction, seismic compression, and landslides. Buried pipelines are relatively insensitive to dynamic ground shaking, provided no permanent displacement occurs. Accordingly, we have developed procedures to develop hazard-consistent evaluations of permanent ground displacements from ground failure.

Most forms of ground failure are a consequence of soil responses to ground shaking. We define ground shaking hazards on a scenario basis to represent spatial correlations of intensity measures. We describe a methodology for identifying hazard-consistent event scenarios that are assigned rates adjusted from those provided by seismic source models so that the collection of scenarios produce composite hazard over many locations (and for multiple intensity measures) that match targets from conventional hazard analysis.

Seismic ground failure responses are evaluated based on regionally-accessible information on geology, groundwater hydrology, and terrain. Given these inputs, liquefaction susceptibility, triggering, and lateral spreading displacements are predicted point-by-point on a 10 m grid using cone penetration test-based models with representative profiles for each Quaternary geologic unit. For each point, these analyses provide probabilities of hazard triggering, probabilistic distributions (accounting for epistemic uncertainties) of related displacements, and displacement directions (azimuths). Series of points expected to move together (i.e., in a single lateral spread) are grouped into features. The sizes and distributions of features across a region are checked against empirical geo-spatial models to avoid bias. The output of these analyses are feature locations, sizes, displacements, and displacement azimuths, which can be applied in subsequent fragility and risk analysis of distributed infrastructure components such as pipelines and reservoirs.