Geophysical surveys are used by geologists to identify underground rock layers. A gravity survey over parts of South Gippsland was completed in July 2014 and a seismic survey has also been undertaken in June and July 2015
These surveys are low-impact and are designed to be non-invasive. Technicians carry out the surveys on foot and in light and heavy vehicles.
A gravity survey measures small gravity variations at individual points on the ground. Rock density varies with rock type (for instance, sandstone density is different to granite) and this affects the Earth’s overall gravity field located near the rock. This minute effect can be measured at the surface with a sensitive weight measuring instrument – a gravity meter. This survey will result in a gravity variation map, and estimated positions and depths to rock features of different density.
Seismic surveys investigate underground rock layers using the same principle as medical ultrasound scanning, but on a larger scale. Rocks of different composition transmit sound waves – generated by a vibrating plate pressed to the ground – at different speeds. This creates echoes that are detected by ground microphones called geophones. The images produced from seismic surveys are cross-sections of the earth, and geologists use these, along with other data such as gravity maps, to accurately predict the depth and size of rock features underground.
Landholders, local communities and other stakeholders will be informed ahead of time about any field work being undertaken.