Hobart sits on a complex geological mosaic of Permo-Triassic sedimentary rocks overlain by Quaternary dolerite and alluvial deposits along the Derwent estuary. The city's seismic hazard is moderate, with design acceleration coefficients around 0.08g for rock sites per AS/NZS 1170.4. For projects requiring detailed subsurface velocity profiling, we deploy seismic tomography (refraction/reflection) surveys to map layer geometry and elastic moduli. This technique resolves contrasts between weathered dolerite, mudstone, and competent bedrock better than conventional refraction alone. Combining it with a [MASW survey](/masw-vs30/) provides shear-wave velocity profiles for site class assessment, while resistivity imaging complements tomographic data in heterogeneous fill zones.
Seismic tomography in Hobart's dolerite terrain resolves velocity contrasts of 400 to 2,800 m/s, critical for classifying site class per AS 1170.4.
Methodology and scope
Local considerations
AS/NZS 1170.4 assigns Hobart a moderate seismicity zone, but the engineered fill over reclaimed waterfront areas near Constitution Dock and Hunter Island amplifies ground motion unpredictably. Seismic tomography identifies zones where weathered dolerite caprock transitions abruptly to competent bedrock — boundaries that differential settlement exploits during earthquakes. Without this data, designers risk misclassifying site subsoil class, leading to under-designed foundations. We cross-check tomographic results with borehole SPT data to validate velocity-to-strength correlations, ensuring the seismic design parameters reflect actual ground conditions beneath Hobart's variable urban geology.
Applicable standards
AS 1726-2017 Geotechnical Site Investigations, AS/NZS 1170.4:2024 Structural Design Actions (Earthquake), AS 1289 Standard Guide for Refraction Seismic Method, Australian Earthquake Loading Standard Commentary (HB 2.2)
Associated technical services
Refraction Tomography for Bedrock Profiling
High-resolution P-wave refraction using tomographic inversion to map weathered dolerite thickness, fault zones, and paleochannels. Typical applications include bridge foundation design, tunnel alignment studies, and quarry development in the Wellington Range foothills.
Reflection & MASW Integration for Cavity Detection
Combined shallow reflection profiling and MASW analysis to locate voids in karstic Triassic limestone or abandoned mining workings beneath Hobart's eastern suburbs. Delivers 2D shear-wave velocity sections and depth-to-void maps.
Typical parameters
Frequently asked questions
What depth range can seismic tomography achieve in Hobart's dolerite terrain?
Refraction tomography typically reaches 15–40 m in weathered dolerite and 10–30 m in reflection mode, depending on source energy and ambient noise. Deeper penetration requires accelerated weight-drop or small explosive sources, subject to council permits.
How does seismic tomography differ from standard MASW surveys?
MASW targets shear-wave velocity (Vs) profiles for site class assessment, while seismic tomography resolves both P-wave and S-wave velocity structures in 2D sections. Tomography is preferred when layer geometry, fault detection, or cavity mapping is the primary objective.
What is the typical cost range for seismic tomography in Hobart?
For a standard 48-channel survey with 200 m spread and basic processing, costs range between AU$4,440 and AU$7,580 depending on site access, source type, and the need for integrated borehole calibration. Larger projects with multiple lines reduce per-line cost.
Do you need council approval for seismic surveys in Hobart City Centre?
Yes, any ground vibration source (weight drop, hammer, explosives) in the Hobart municipal area requires a Development Application or at least a Road Occupancy Permit for urban streets. We handle the permit process and notify nearby residents when required.