Fresno grew fast after the 1872 Lone Pine earthquake proved the Sierra Nevada front is seismically alive. That early shock, felt across the San Joaquin Valley before the city had paved roads, is a reminder that soft basin deposits amplify ground motion. The team works on sites underlain by Holocene alluvium from the Kings and San Joaquin rivers—loose sands and silts deposited in the last 10,000 years. When groundwater sits within 50 feet of the surface, these layers become prime candidates for cyclic mobility and flow failure. A seismic microzonation study helps map the spatial variability of risk across the city, while CPT sounding delivers a continuous profile of tip resistance and pore pressure to flag thin liquefiable seams that SPT alone might miss.
A factor of safety below 1.0 in a liquefaction analysis means the soil strength drops to near zero during shaking: the foundation must be redesigned.
