AuScope earthquake hunters catch record-breaking quake

A trace of this morning’s mainshock (left cluster) and three aftershocks (small clusters to the right of the mainshock) that were sensed by NCRIS enabled seismometers located permanently in the region. Image: Abraham Jones / Seismology Research Cent… — A trace of this morning’s mainshock (left cluster) and three aftershocks (small clusters to the right of the mainshock) that were sensed by NCRIS enabled seismometers located permanently in the region. Image: Abraham Jones / Seismology Research Centre — EQserver

Hold onto your coffee cups and comfort the dog. This morning’s earthquake in southeastern Australia, which is perhaps the largest in the region in 200 years, thankfully has not yet caused any injuries. It has, however, provided AuScope geoscientists with the opportunity to put their earthquake hunter hats on and investigate this record-breaking moment. Here are their thoughts!

Where were you when the earthquake struck this morning, and what happened?

Dr Tim Rawling, CEO and Director of AuScope responds:

“I was sitting in my home in St Kilda, Melbourne, chatting on a Zoom with collaborators from Geoscience Australia in Canberra when the earthquake started. One minute later, my collaborators on the call in Canberra felt the quake and we knew it must have been big! Afterwards, I went to check out the recording on the seismometer next to me. It never fails to amaze me how dynamic our Earth is...”

Dr Graeme Beardsmore, Senior Fellow In Crustal Heat Flow was close to the action:

“I was at home with my 10-year-old son in his room when it struck. We moved under his doorway as a precaution as the shaking increased to its maximum. He was excited more than scared, although he admitted he might have been scared if I hadn’t been right there.
We went out exploring shortly afterwards, saw the collapsed wall in Windsor, and I used that to explain that the waves were coming from the north so the east-west aligned wall was at the most vulnerable angle.”

Damage to masonry 100m from Dr Graeme Beardsmore consulting office in Windsor, around 130 km from the earthquake epicentre in Mansfield, Taungurung country! Image: Supplied

How did we measure it?

Aside from noticing our desks rattle and roll, geoscientists were able to capture this earthquake across our NCRIS and AuScope enabled network of seismometers located all around Australia, and with the digital platform enabled by Geoscience Australia. We can also trace the seismic waves from further afield using international seismic surveys such as the United States Geological Survey.

The dashboard of USGA featuring all the information gathered so far on the Mansfield quake. Image: USGA

What is the significance of this earthquake?

A map of Australia showing the location of all historical earthquakes between the years 1900 – 2000 that are greater than magnitude 6 in size. Image: Dr Januka Attanayake, Geoscience Australia

Dr Januka Attanayake, earthquake seismologist from The University of Melbourne explains:

“If the preliminary magnitude of 5.8 is correct, this is the biggest event in the last 200 years in the southeastern part of onshore Australia. If it were to be revised to 6.0 later on with precise measurements, this is the first time we would have broken that seismic ceiling in our recorded catalogue in the same region.”

Fielding the questions…

LISTEN to Dr Michelle Salmon as she chats with Stephen French about earthquakes and Australia.

Dr Michelle Salmon, seismologist from AuScope and the Australian National University, has been on the phone all day tackling questions from the concerned and the curious. Her radio interview with Stephen French is available here. Prof. Mark Quigly, an AuScope collaborator from The University of Melbourne has also been fielding the media’s questions and filling in the details for the curious public in his article for The Conversation.

How can you get involved?

The internet has made following earthquakes in real-time possible for everyone. The team at Geoscience Australia have a live portal for all things seismic. You will find today’s Mansfield earthquake captured and listed on their site with information on magnitude, time and a felt cluster map. This is a crowdsourced impact map that you can contribute to. Thousands of responses are in already and they are a crucial source of information for geoscientists on the felt experience of this record-breaking earthquake.

Felt cluster map from Geoscience Australia. Record your experience and contribute to the live mapping of the Victorian earthquake. Source: Geoscience Australia

The next steps in tracking this earthquake?

It is now late in the day, but Abraham Jones, Network Manager from the Seismology Monitoring Network (SMN) and the team at The University of Melbourne is just getting started with their aftershock investigation. First, the SMN team are assembling NCRIS enabled seismometers and obtaining permits with the intention of heading up to the area tomorrow to install some temporary seismometers in the region to record the aftershock sequence. Abe comments:

“We are already recording quite a few of the larger aftershocks using seismometers in the Gippsland area, but to locate them with higher precision, we need to install instruments closer to the epicentre. We need to find quiet spots to place the instruments away from highways, either just below the soil surface or on rock outcrops.”

The most important thing for the SMN team in this mission is to get there fast:

“The aftershocks frequency and magnitude decrease quickly in the hours and days after the mainshock, so we are keen to get out there in the next few days to ensure that we capture as much data as possible for research.”

The data that the SMN collects will help to bring greater accuracy to the earthquake epicentre, its magnitude, and also the depth of its source below the Earth. Abe explains:

“We are keen to gain a greater understanding of not just the epicentre of the main earthquake, which is the spot on the surface of the Earth where the earthquake was felt greatest, but also the hypocentre, which is the depth of where the shaking first began. Most media are reporting a hypocentre of 10km, but we will be able to find a more accurate depth with new data.”

Abraham inspects data on screen by an AuScope enabled seismometer in Gippsland (left) and small signs of surface rupture caused by the main earthquake or its aftershocks (right). Images: supplied in the days after the main earthquake and after this story was originally published, both on Wednesday 22 September 2021.

What does it feel like to be an earthquake hunter right now?

Who better to ask than the aftershock seeker himself, Abraham Jones:

“It’s exciting! It’s not every day that something like this happens, and that we get an opportunity to research a new earthquake and get this story out there to everyone that Australia does, indeed, have earthquakes.
The length of the earthquake surprised me, as the shaking continued, I knew it must be a big event. I felt the Moe-Thorpdale in 2012 and aftershocks of the Petermann Earthquake in 2016. But this felt much stronger.”

AUTHORS
Philomena Manifold and
Jo Condon (AuScope)

AUSCOPE COLLABORATORS
Dr Tim Rawling, Abraham Jones,
Dr Graeme Beardsmore, Dr Januka Attanayake, Dr Michelle Salmon, Prof. Mark Quigly and Abraham Jones