HVSR Microtremor Survey Sydney – Nakamura Method for Seismic Site Response

HVSR measures the horizontal-to-vertical spectral ratio of ambient vibrations to find the fundamental resonance frequency (f0) of the soil column. MASW directly measures shear-wave velocity with depth to compute Vs30. HVSR is faster (hours per station), works better on stiff sites where Vs30 contrast is low, and is less affected by lateral soil changes. MASW provides depth profiles; HVSR provides the resonant behaviour that actually controls seismic response. We often use both together—HVSR to map frequency variability across a large site, then targeted MASW to calibrate Vs30 for the design spectrum.

For a typical residential or commercial site of 0.2–0.5 ha with 4–6 measurement stations, the total cost including acquisition, processing, and a report with interpreted f0 and site class ranges from AU$2,240 to AU$3,680. Larger sites or those requiring additional stations for variability mapping fall at the upper end. Prices exclude access permits, traffic management, and any supplementary borehole data integration.

HVSR detects the interface corresponding to the largest impedance contrast in the top few hundred metres. In Sydney, that contrast is typically the soil–bedrock interface, which can be 2 m deep in the eastern suburbs or over 40 m deep in the Parramatta alluvial basin. The method does not resolve layer-by-layer profiles—that requires MASW or boreholes. Instead, it tells you the natural period of the entire soil column, which is the key parameter for evaluating resonance with a building’s fundamental period.