Soils in downtown Austin’s urban core behave nothing like the deep clays along the Colorado River floodplain. That contrast is exactly why a one-size-fits-all seismic approach fails here. Our team has mapped response across both settings. For shallow limestone near the capitol we rely on resistivity surveys to detect bedrock depth. Over the alluvial deposits east of I-35 we deploy microtremor HVSR to capture fundamental frequency. Seismic microzonation in Austin must start with a clear picture of the local geology — not a generic code table.
Without measured VS30 profiles, the IBC site class is just a guess. Seismic microzonation turns that guess into a defendable design basis.