Beetaloo Sub-basin Seismic Monitoring Project
Figure 1: The Beetaloo Sub-basin region relative to the existing Australian National Seismic Network (red circles) in northern Australia.
Geoscience Australia is Australia’s pre-eminent public sector geoscience organisation and is the Australian Government's trusted advisor on the geology and geography of Australia. Geoscience Australia is partnering with the Department of the Environment and Energy’s Geological and Bioregional Assessment (GBA) Program to provide information that will help assess the environmental impacts of shale and tight gas development in the Beetaloo Sub-basin region of the Northern Territory. Through the GBA program, Geoscience Australia will install a seismic monitoring network in the Beetaloo Sub-basin region. This network will detect and locate natural seismic activity (i.e., earthquakes) in the area, as well as human-induced seismicity as a result of hydrocarbon extraction activities. This information will be used by Geoscience Australia, the public and other organisations to build knowledge about potential human-induced seismic activity in the region that may be associated with hydrocarbon extraction activities such as hydraulic fracturing.
What is seismicity?
Seismicity is a term that is used to describe the occurrence of seismic events, such as earthquakes. An earthquake is the rapid release of energy when stresses in the Earth’s crust cause rocks to break and move along faults deep underground. This energy is felt at the Earth’s surface as vibrations and shaking. Most earthquakes occur naturally due to the build-up of stresses in the Earth’s crust over long periods of time (often hundreds or thousands of years). Earthquakes most commonly occur near the boundaries of tectonic plates, such as around the “Pacific Rim of Fire.” However, they can also occur within stable tectonic regions, like Australia. Significant earthquakes in the Northern Territory include the magnitude 6.2, 6.3 and 6.6 earthquakes near Tennant Creek in 1988 and the 2016 magnitude 6.1 Petermann Ranges earthquake.
What is induced seismicity?
Induced seismicity is the term used to describe earthquakes caused by human activities. These events can be triggered as a result of a range of common industrial activities, such as some types of mining, geothermal energy production, the filling of large water reservoirs, and the extraction of oil and gas, including through hydraulic fracturing. Hydraulic fracturing (or “fracking”) is the process of injecting fluid at high pressures into the Earth to create or open existing cracks in rocks so that other fluids (in this case oil or gas) can move through the rock. It is important to note that only a small fraction of hydraulic fracturing activities worldwide induce earthquakes that are large enough to be felt at the Earth’s surface.
How do we monitor seismicity?
While the vast majority of earthquakes induced by human activities are very small and cannot be felt at the Earth’s surface, we are able to detect these earthquakes and other ground vibrations using sensitive instruments known as seismometers. Vibrations can also be detected from local and distant natural earthquakes, mine blasts or explosions, waves breaking on the sea shore, and even wind. Effectively monitoring a region for small-magnitude earthquakes requires the deployment of multiple seismometers so that earthquake-generated shaking can be measured and “triangulated” to determine the location and size of an earthquake. Earthquakes can only be located if they can be detected at three or more stations.
Installing the seismometers is a simple process and causes minimal disturbance to the land (see Figure 2). The seismometer is a passive sensor and does not emit any other signal or generate vibrations itself.
About the Beetaloo Sub-basin project
Seismic stations are expected to be installed in two phases. In Phase 1 (expected late 2019; Figure 3), 10 temporary seismic stations will be installed in order to begin monitoring immediately. For Phase 2, 10 seismic stations with satellite communications equipment will be installed (expected mid-2020). These sensors are more complex and require more time to install. The Phase 2 deployments will provide Geoscience Australia with data via satellite to monitor regional seismic activity in real time. All data will be made freely available and any seismic activity recorded in the Beetaloo Sub-basin region during this monitoring period will be reported in either official Geoscience Australia written records or via the earthquakes.ga.gov.au webpage.
The precise station location and installation timing of the new network will be determined in consultation with traditional owners and land holders, and after the appropriate permissions have been obtained. The sites will be accessed by small teams using either vehicles or helicopters. Existing roads and tracks are used if available, though some areas may require off-road access.
- For seismic data and reports visit earthquakes.ga.gov.au
- For more information and products on Geoscience Australia’s role in reducing risk to Australians from earthquakes, please visit our Earthquakes webpage.
- Geoscience Australia are partnering with the Geological and Bioregional Assessment Program to undertake this project. Find out more about the program here.