ASCE 7-22 and the California Building Code require site-specific ground motion analysis for structures on Site Class D through F. In Pomona, this is not a formality. The city sits on a complex alluvial fan where the San Jose Fault and the Cucamonga Fault Zone influence subsurface conditions. We prepare microzonation studies that map spectral acceleration, site period, and amplification factors across a parcel. Our team has run dozens of CPT soundings and borings in the area, and we know the difference between the stiff gravels near Fairplex and the deeper fine-grained deposits south of the 60 freeway. The CPT test gives us continuous stratigraphy, which we pair with downhole seismic data to constrain shear wave velocity profiles. For sites with variable fill, we also rely on test pits to document old debris and undocumented compaction.
Vs30 alone is not enough in Pomona. We map site period and basin-edge effects to avoid underestimating long-period amplification.
