In Fresno, we see a recurring pattern that keeps engineers up at night: structural designs based on generalized county-level hazard maps that completely miss the alluvial fan complexities beneath the site. The San Joaquin Valley isn't uniform—it is a deep sedimentary basin where the impedance contrast between soft near-surface deposits and stiffer Pleistocene layers can amplify seismic waves in ways that a zip-code approach simply ignores. We combine MASW surveys for Vs30 profiling with deep borehole data to capture the actual site response. Fresno sits about 50 km from the San Andreas Fault, but the real story is local: Quaternary alluvium overlying the Tulare Formation creates resonance frequencies that affect mid-rise structures far more than rock-outcrop models predict. This is what microzonation solves.
A basin-edge effect measured 3 km from your site can double the short-period spectral acceleration compared to the USGS NSHM value—we’ve documented it in eastern Fresno.
