Seismic drumroll for Hazelwood chimney departure
Footage of the demolition of the chimneys at the Hazelwood coal-fired power station in Victoria, Australia. Video: ABC Australia
In May 2020, we witnessed dramatic footage of eight chimney stacks at the old Hazelwood coal-fired power station sequentially fall during demolition. AuScope seismometers (earthquake recording instruments) located across the region recorded the shock, as they do many different natural (e.g. earthquakes) and human made (e.g. quarry blasts, explosions) events in Australia and around the world.
Here’s what scientists can learn using this NCRIS enabled seismic data.
Detecting the Hazelwood demolition
Some man-made (anthropogenic) events excite seismic waves in the subsurface similar to those emanating from earthquakes. Seismic waves radiated by anthropogenic events transmitting large amounts of energy (e.g. nuclear explosions) are recorded by seismic stations distributed globally, whereas events releasing smaller amounts of energy (e.g. moving trains) radiate weaker seismic waves that are detected only by stations located much closer to the point of origin.
Just after midday on the 25th May 2020, the demolition of eight 137 metre tall chimney stacks at the now-decommissioned Hazelwood brown coal power plant in the Latrobe Valley excited seismic ground motion that was detected by AuScope and University of Melbourne seismometers in eastern Victoria.
The AuScope/UoM seismometer (MARD) sensor is located 28 km from the Hazelwood power plant. Image: Supplied
Using data recorded by a sensor located 28 kilometres from the power station, we estimate that the initial detonation charges were approximately equivalent to Local Magnitude (ML) 0.8 earthquakes. The peak recorded ground motion occurred when a detonation charge combined with the concurrent collapse of a chimney stack to produce seismic amplitudes similar to what would be expected from a ML 1.6 earthquake.
Seismogram of the Hazelwood chimney stack demolition (top), and a spectrogram showing the frequency signature of these signals (bottom). Data recorded by the AuScope/UoM seismometer 28km away. Image: Supplied
Analysis of anthropogenic and natural energy sources can both contribute to our understanding of the earth’s subsurface. Whilst we use the location of earthquakes to pinpoint regions of the earth’s crust where there are faults, the travel times of seismic waves from man-made sources with known origins (such as the chimney collapse) enable us to precisely determine subsurface seismic velocity structure and correlate it with underlying geology and infer dynamics of our planet’s interior.
Detecting other kinds of ground motion
Seismologists use seismic travel time and waveform data to locate earthquakes, determine the physics of earthquake processes, and delineate fault zones, image the subsurface and infer geodynamics in deeper regions of the solid Earth inaccessible to direct human observation, monitor urban activity, weather, and environmental processes, characterize onshore and offshore human activity for forensic purposes, and even time touchdowns in a game of American football (who needs a TV anymore!).
Here in Australia, contrary to the popular belief, numerous smaller earthquakes occur frequently, although larger damaging earthquakes are fairly rare. Based on the national seismic hazard map, the southeastern corner of the Australian continent is an earthquake hotspot.
Earthquakes located in South-East Victoria since 2017 (red) and between 1800 – 2017 (grey). Image: Supplied
The University of Melbourne, in collaboration with AuScope, maintains Australia’s most precise continuous seismic monitoring network in this region with a demonstrated minimum detection magnitude threshold of ML -0.5, and a magnitude of completeness (the magnitude above which all earthquakes are recorded within the network) of ML 0.5.
Using this state-of-the-art network comprising 39 seismic instruments developed largely in the last three years with financial support from the (now closed) Education Infrastructure Fund (EIF) in association with the Victorian Government’s CarbonNet Project, the Australian National Low Emissions Coal Research and Development initiative (ANLEC R&D), and AuScope, we have detected and located more than one thousand small earthquakes in south-east Victoria alone, including some of which were felt locally.
This new high resolution dataset is allowing us to compute more robust earthquake statistics including recurrence intervals and map out spatial variations in seismic activity in southeast Australia.
Our network can also be used to locate larger earthquakes occurring elsewhere in Australia and around the world. For these distant events, data from the UoM network is used alongside that recorded by the Australian National Seismograph Network managed by Geoscience Australia, and the Australian Seismometers in Schools network (AuSIS).
The University of Melbourne’s seismic monitoring network in South-East Victoria. Image: Supplied
For instance, over the last 10 years, these seismic networks have allowed us to record and research significant events such as the magnitude 4.9 Thorpdale Earthquake in 2012 which was strongly felt across eastern Victoria and in Melbourne, and the 2016 magnitude 6.0 Petermann Earthquake in the NT which was the largest Australian earthquake for almost 20 years.
Here we demonstrate a further application of our data in monitoring anthropogenic sources of seismic energy rather than natural seismic events.
Abraham Jones installing broadband seismometers in Gippsland. Stations such as this were used to record the Hazelwood chimney collapse and the 2012 Mw 4.9 Thorpdale Earthquake which shook the region. Image: Supplied
Future of seismic monitoring and research
As our event map shows, numerous small earthquakes have occurred in the last three years. These occur on deep faults that cannot be directly investigated but are potentially capable of producing damaging earthquakes such as the 2012 Thorpdale earthquake or even larger events. Therefore, we rely on precise remote earthquake signals recorded by our seismic network to better understand earthquake source processes, fault distribution, crustal deformation, and seismic hazard in eastern Victoria.
This new knowledge helps us determine the nature of tectonic processes in plate interiors in general and ensure the security of a plethora of critical infrastructure (power plants, water supply, gas pipes, roads etc.) located in Victoria against possible damaging earthquakes. Further development of this seismic monitoring infrastructure (e.g. installation of new stations) and far-reaching research work (e.g. improving earthquake detection and location algorithms) would not be possible without the continued generous support of AuScope, ANLEC R&D, CO2CRC, The CarbonNet Project, and other external partners.
AUTHORS
By Abraham Jones, Dr Januka Attanayake, and Dr David Belton,
The University of Melbourne
EDITOR
Jo Condon, AuScope
MORE INFORMATION
Please contact Abraham Jones
to learn more about this story