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WITHDRAWN A Remarkable Absence of Liquefaction: Data-Driven Lessons From the 2014 South Napa Earthquake

Description: 

WITHDRAWN The M6.0 2014 South Napa earthquake is often recognized for having a remarkable absence of liquefaction. But why? We investigate the subsurface soil and groundwater conditions in the vicinity of the fault rupture to determine the potential reasons that liquefaction observations were nearly absent, despite rigorous reconnaissance efforts. Through an analysis of several thousand borehole-based samples and monitoring well observations, we determined that the near absence of liquefaction was not remarkable but was rather predictable. First, the borehole data in the vicinity of Napa indicate that the Holocene alluvial soils tend to be more clay-like than elsewhere in the San Francisco Bay region. Second, the groundwater at the time of the earthquake was significantly lower than the typical elevation due to a prolonged drought. The combination of these factors resulted in a low probability of liquefaction.

While the low groundwater levels at the time of the earthquake were fortuitous from a liquefaction perspective, groundwater levels can be highly variable. We also investigate the potential for liquefaction under different groundwater conditions with a novel spatial and temporal groundwater model. The groundwater model is based on a relatively simple 2D flow analysis coupled with a Gaussian Process regression scheme to interpolate the groundwater elevation between well observations. The analyses indicate that if the earthquake had occurred during typical, non-drought conditions, the liquefaction ground damage would have been more severe. Likewise, the influence of sea level rise associated with climate change impacts groundwater conditions, which would further increase the probability of liquefaction.

Session: Regional-Scale Hazard, Risk and Loss Assessments [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Michael

Student Presenter: No

Invited Presentation: 

Authors