The subsurface contrast between a Midtown Manhattan office tower and a low-rise residential block in southeast Queens is not just about foundation depth: it is about how the ground will shake during an earthquake. In Midtown, competent Manhattan Schist lies within a few meters of grade, producing short-period amplification that can concentrate energy at frequencies damaging to mid-rise steel frames. Out in the fill-and-marsh deposits of JFK's periphery, deep Holocene sediments stretch 30 meters or more, shifting the resonant period downward and threatening taller structures with long-period amplification. Our seismic microzonation work maps these transitions block by block, delivering shear-wave velocity profiles, site class per ASCE 7-22 Chapter 20, and two-dimensional amplification functions that structural engineers need for drift checks and base shear calibration. We have measured Vs30 values below 180 m/s in Staten Island's organic silts and above 760 m/s on the Fordham Gneiss, and that 600 m/s spread changes the seismic coefficient by a factor of two. For sites where the rock head dips abruptly, combining the microzonation with a CPT test resolves the soil column stiffness without the sample disturbance that rotary borings cause in varved clays.
In New York's glacial terrain, a 50-meter lateral shift in bedrock depth can double the spectral acceleration at the ground surface.
