Stockton sits on deep alluvial soils where the San Joaquin and Calaveras river systems have deposited loose sands and soft clays for millennia. The 1989 Loma Prieta earthquake, centered 70 miles away, still produced Modified Mercalli Intensity VI shaking here — a direct result of site amplification across the basin. Our seismic microzonation work quantifies that risk block by block. We measure shear wave velocity profiles, map the fundamental period of each deposit, and classify ground types per ASCE 7-22. For projects near the Port of Stockton or the Eight Mile Road corridor, we often combine this with liquefaction triggering analysis because the water table sits barely 5 to 10 feet below grade across much of the city. The deliverable is a ground response map that engineers use to anchor spectral accelerations to site-specific conditions instead of default code values.
Site Class E soils in Stockton can amplify short-period ground motion by 40% more than a rock outcrop at the same distance.
