Our crew rolls out with a portable seismograph and a 24-channel geophone array to perform seismic amplification analysis in Bendigo. The rig is compact enough to maneuver along the narrow streets of the Golden Square area, where older buildings sit close to the lot line. We couple the geophones directly to the ground using base plates and a sledgehammer source. The raw data goes straight to a laptop running inversion software. We process it onsite to check for coupling issues before packing up. This approach follows the AS 1289 standard for surface wave testing, and we cross-check results against borehole data from the same investigation. The whole setup takes about three hours per line, including walk-away shots.
A sharp impedance contrast between alluvial clay and weathered siltstone can double the peak ground acceleration at the surface.
Methodology and scope
In Bendigo we often see stiff alluvial clays overlying weathered siltstone, which creates a sharp impedance contrast. That boundary can amplify ground motion during an earthquake, so we run a MASW-Vs30 survey to capture the shear-wave velocity profile down to 30 meters. The inversion gives us the time-averaged Vs30 needed for site class assignment per AS 1170.4. We also deploy a resistivity survey to map the depth to bedrock laterally. The combination of seismic and electrical methods reduces uncertainty in the amplification factor. Every report includes a site-response curve calculated with equivalent-linear analysis using the measured shear-modulus reduction curves.
Technical reference image — Bendigo
Local considerations
The goldfields region around Bendigo sits in a moderate seismic zone, with historical events reaching magnitude 5.0. The shallow soil profile amplifies long-period motion, which can damage unreinforced masonry walls common in the city's heritage buildings. A poorly characterized amplification factor leads to under-designed foundations or excessive retrofit costs. Our analysis quantifies the actual site response so engineers can design for the real shaking demand rather than relying on blanket code values. We flag any liquefaction-susceptible layers identified during the borehole campaign and cross-reference them with the amplification curves.
Multi-channel analysis of surface waves to generate a shear-wave velocity profile down to 30 m. Used to assign site class per AS 1170.4 and to compute the fundamental period of the soil column.
02
Equivalent-Linear Site Response
We take the Vs30 profile and run an equivalent-linear analysis using modulus reduction and damping curves from the measured soil type. Output includes acceleration time histories, response spectra, and amplification factors for the design bedrock motion.
Applicable standards
AS 1170.4:2007 (Earthquake actions), AS 1289 (MASW testing), NEHRP site classification (FEMA P-749)
Frequently asked questions
What is the difference between seismic amplification analysis and a standard geotechnical investigation?
A standard investigation focuses on bearing capacity and settlement. Seismic amplification analysis specifically evaluates how the soil column modifies earthquake ground motion. It uses shear-wave velocity data, site-response software, and site-specific input motions to produce amplification factors and response spectra for structural design.
How much does seismic amplification analysis cost in Bendigo?
The cost typically ranges between AU$1,610 and AU$3,130 depending on the number of MASW lines, the depth of profiling, and whether you need full equivalent-linear analysis. We provide a fixed quote after reviewing the site area and access conditions.
When is seismic amplification analysis required for a project in Bendigo?
It is required for all Importance Level 2 and above structures under AS 1170.4 when the site class is unknown or when the design spectrum needs site-specific refinement. We also recommend it for retrofit of heritage buildings in the city center, where the stiff clays over siltstone can amplify motion significantly.
What data do you need from me to start the analysis?
We need the site plan showing building footprint and any existing borehole logs. If you have previous geotechnical reports, include them. We also need permission to access the site for the MASW survey, which requires a clear line of about 70 meters. No drilling is needed for the seismic testing alone.
