Working across Geelong, we often see that the subsurface conditions vary significantly between the Barwon River flats and the volcanic plains to the north. Seismic tomography provides a continuous velocity profile that helps identify these transitions without relying solely on boreholes. For projects requiring detailed stratigraphy, we pair refraction tomography with georradar-gpr to cross-check shallow anomalies, and when depth penetration beyond 30 m is needed, reflection methods offer better resolution of deeper interfaces.
Continuous velocity profiling via seismic tomography reveals hidden interfaces that discrete boreholes can miss, especially across Geelong’s basalt-sediment transitions.
Scope of work in Geelong
- Refraction: P-wave velocity profiling to 30 m depth, ideal for rippability and rockhead mapping
- Reflection: S-wave or P-wave imaging for fault detection and bedding geometry, down to 100 m
Demonstration video
Typical technical challenges in Geelong
Geelong sits within a moderate seismic zone, with the 2012 Moe earthquake (M5.3) reminding us that even low-magnitude events can affect soft alluvial soils along the Barwon River. Without seismic tomography, the velocity contrast between stiff basalt and loose sediments remains unknown, leading to incorrect site class assignments under AS/NZS 1170.2. We routinely map these contrasts to guide foundation design and mitigate differential settlement risk in new developments.
Our services
We offer two complementary seismic tomography services tailored to Geelong site conditions.
Refraction Tomography
P-wave velocity profiling for rockhead mapping, rippability assessment, and excavation classification. Ideal for road cuts and foundation investigations in the You Yangs foothills.
Reflection Seismics
High-resolution imaging of dipping strata and fault zones, used for tunnel alignment studies and deep foundation design in Geelong’s older volcanic terrain.
Frequently asked questions
What is the difference between refraction and reflection seismic tomography?
Refraction tomography measures first-arrival P-waves to build a velocity model of the shallow subsurface (typically 5–30 m depth), while reflection seismics records both P- and S-wave reflections to image deeper structures like bedding planes and faults down to 100 m. Refraction works best for horizontal layers; reflection handles dipping interfaces better.
How much does a seismic tomography survey cost in Geelong?
For a typical 120 m line with 24 geophones, the cost ranges between AU$4,530 and AU$8,610 depending on access, source type, and processing complexity. Additional lines or deeper reflection surveys increase the price.
Can seismic tomography detect groundwater or voids?
Seismic tomography can identify low-velocity anomalies that may indicate voids or water-saturated zones, but it is not a direct groundwater detection method. We often combine it with electrical resistivity tomography for better discrimination between air-filled voids and water-filled cavities.
What site conditions affect seismic tomography quality in Geelong?
Surface noise from nearby roads, basalt caprock that scatters energy, and clay-rich soils that attenuate signals can reduce data quality. We mitigate this by using higher source energy, increasing geophone spacing, and applying bandpass filtering during processing.