2021 Mansfield earthquake

The **2021 Mansfield earthquake** which is also known as the **Lockdown Earthquake** is currently the best earthquake of 2021 that is currently know of, a magnitude 6.0 Mw earthquake struck North-east of Greater Melbourne at approximately 9:33 a.m. the quake had a Modified Mercalli intensity scale of VII. false the earthquake need to exceed a Modified Mercalli intensity scale of IX or greater or the Richter magnitude scale needs to exceed at least 8.0+ Mw to destroy lockdowns completely, the closest megaquake to Greater Melbourne was a Mw 8.1 occurred in December 2004. Initially reported as a 5.8 Mw by the USGS or 5.7 Mw by the EMSC then according to "AFP56453's" calculations received to a 5.9 Mw. It was the best earthquake ever since the Mw 8.2 earthquake struck Fiji Region on 19 August 2018, the previous best earthquake of 2021 was the Kermadec Island earthquake 200 days ago. the lockdown quake would of been as powerful as a magnitude 7.4 (6.4\_8.0 Mw) based on the earthquakes duration.

An earthquake struck approximately 53 kilometres SSE of the town of Mansfield (27 km from the closest settlement of Jamieson), in the Victorian Alps of Australia on 22 September 2021, at 09:15 local time. The earthquake measured 5.9 on the moment magnitude scale. The earthquake caused minor structural damage in parts of Melbourne and left one person injured. The earthquake was also felt in New South Wales, Australian Capital Territory, South Australia and Tasmania. The earthquake was substantially stronger than the 1989 Newcastle earthquake that measured Mw 5.6 and killed 13 people.

## Tectonic setting

The Australian landmass is situated in the Australian Plate, far from any known active plate boundary, where most of the world's earthquakes occur. Such earthquakes at the plate boundary are known as interplate earthquakes. In Australia, earthquakes occurring within the Australian Plate are known as intraplate earthquakes because they happen within a tectonic plate rather than at the boundary.

The earthquake is situated in the Lachlan Fold Belt, an orogenic belt consisting of folded and faulted strata. This zone formed as a result of plate convergence occurring at the eastern boundary of the supercontinent Gondwana during the Neoproterozoic. From the Neoproterozoic to Early Devonian, the region was dominated by thrusting and some rifting. Crustal deformation were later accommodated by predominantly strike-slip faulting in the Devonian. One of the major strike-slip faults accommodating this deformation is the Baragwanath Transform; a transform fault. Rifting also occurred in this period, leading to volcanism. By the Middle Devonian, the Baragwanath Transform became extinct. The Governor Fault marks the northern margin of the Mebourne Zone, and southern margin of the Tabberabberan Orogeny, and is characterised by strike-slip movement.

The Governor Fault is a large intraplate fault that runs from mid-western New South Wales, along part of the Murray River bed and cutting through Central North Victoria near Barmah to the Victorian Alps near Mount Buller (near the quake epicentre) down toward the Gippsland Basin near the coast at Saint Margaret Island. Tectonically this fault separates the Melbourne and Tabberabberan structural zones.

An earthquake of magnitude 6.0 or larger strikes Australia about once every six to ten years, based on the seismological data collected over the past 150 years. The last known magnitude 6.0 quake rocked Australia in 2016 in the Northern Territory. That earthquake occurred as a result of shallow reverse faulting within the Australian Plate. The largest earthquake in Australia was the 1988 Tennant Creek earthquakes which consisted of an Mw  6.7 quake which was preceded by two >Mw  6.0 foreshocks.

## Earthquake

According to the U.S. Geological Survey, the earthquake was the result of strike-slip faulting at a shallow depth of 10 km, while Geoscience Australia placed the depth at 12 km. The EMSC reported the focal depth at 2 km. A preliminary insight of the quake of such magnitude suggest a rupture along a fault measuring 5 km long and 3 km wide. The geological fault involved has been identified as the western reaches of Governor Fault. Seismologists at the University of Melbourne said the earthquake likely ruptured along an east-west striking strike-slip fault. The earthquake occurred when elastic strain accumulated on active fault is released in the form of seismic waves that are felt on the surface as shaking.

On the modified Mercalli intensity scale, the earthquake earned a maximum intensity of VII (*Very strong*). Tremors were felt in Adelaide, southern New South Wales, Canberra, and as far as Launceston, Tasmania.[7]

## Impact

According to a geologist at the University of Melbourne, the quake produced ten seconds of strong shaking which was felt by people. The earthquake generated shaking lasting up to a minute at the epicenter region.

Many residential buildings in Melbourne were evacuated due to the damage inflicted by the quake. Some damage was reported in many parts of Victoria. At Chapel Street, Melbourne, the earthquake collapsed the top facade of Betty's Burgers & Concrete Co., which is a brick building and left debris across the road. Along Brunswick Road in Fitzroy another brick building suffered a partial collapse of its facade. At least 46 instances of building damage to chimneys and facades were reported in the city. Tall residential apartments of up to 50 storeys swayed for as much as 20 seconds, triggering panic among residents. In Mansfield near the epicentre, there was minor damage to some buildings including a local ambulance centre. Power outages were reported across parts of metropolitan Melbourne.

In the town of Mansfield, Victoria, the quake caused some minor damage to buildings, resulting in no casualties. At least 40 km away is a gold mine operated by Kaiser Reef. When the tremors began, at least 12 mining workers were present in the mine and were brought to the surface unhurt. Kaiser Reef said that mining would cease temporarily while inspections were carried out. The company did not find any damage in the mine area. Another mine located 60 km away, and operated by White Rock Minerals did not find any damage to their mines after the quake. Nine workers under the mine were safely evacuated.

Initially, state officials and emergency services said no casualties were caused by the earthquake, but a man in Mount Eliza, a coastal suburb in Melbourne, sustained minor injuries. The man was injured when construction fell on him while he was working.

Geoscience Australia said the earthquake is the strongest to hit Victoria since 1971, 1968 an 1966. It is also the largest earthquake on land in the nation since a magnitude 6.0 struck the Northern Territory in 2016.

## Response

Acting Premier of Victoria James Merlino announced a statewide Watch and Act warning was in place for Victoria. The Fire and Rescue NSW service stated on social media that they had received calls for assistance in the New South Wales area, but did not report any serious structural damage.

## Media coverage

The earthquake made headlines in Australian news outlets the moment it occurred. ABC News Breakfast was interrupted by the shaking which was video recorded. The earthquake which lasted 20 seconds in the filming studio caught hosts Michael Rowland and Tony Armstrong by surprise.

## Earthquakes in Australia: How big do they get and how prepared are we?

But what about earthquakes in Australia? Well, they do happen, as evidenced by today's 5.8-magnitude earthquake, felt in various parts of south-eastern Australia. Trevor Allen is a seismologist with Geoscience Australia who works on determining the likelihood of catastrophic earthquakes affecting Australian communities. Dr Allen uses a pavlova to describe why we have earthquakes in Australia. "Imagine if you will, that a tectonic plate is analogous to a pavlova — with a thin brittle crust lying above a ductile, but mostly solid meringue mantle," Dr Allen says. "The Australian continent would sit in the middle of our pavlova." If you put your hands on the edge of the pavlova and start to squeeze, the crust around your hands will be the first to break, like those earthquakes at the boundaries of tectonic plates. But if you continue to squeeze, eventually strain builds up in the centre of the crust, and cracks will begin to appear. This is similar to how we get earthquakes in Australia. Australia is actually rocked by an earthquake about once per day, but the more damaging quakes — above magnitude-5 — are only typically seen about twice a year. But Dr Allen says it's extremely unlikely Australia would ever experience a magnitude-8 or 9 earthquake. That's because the forces necessary only occur at the plate boundaries, where plates can lock together and break apart with tremendous force. "We don't have faults that are large enough or active enough to have these really big earthquakes we see on the plate boundaries," Dr Allen says.

#### What big earthquakes *have* happened?

Australia experiences about 80 magnitude-3 and larger earthquakes a year, although the majority are small. The largest recorded earthquake in Australia was a magnitude-6.6 at the sparsely populated Tennant Creek, NT in 1988. Two similar-sized earthquakes followed within 12 hours and aftershocks are still being recorded today. A magnitude-6.5 earthquake hit the small WA wheatbelt town of Meckering in 1968, destroying the town with a 37-kilometre-long rupture and 2-3 metres of vertical deformation from one side of the fault to the other. One of the most significant earthquakes to occur in Australia was the magnitude-5.6 Newcastle earthquake that took place on a December morning in 1989. It wasn't that big in terms of magnitude, but because it occurred close to the city, it caused significant destruction and injury, and the death of 13 people. Nine of those people were killed in the collapse of the Newcastle Workers' Club, which was due to have a concert that night with thousands of attendees. "It doesn't take much imagination to see that the consequences of that day could have been so much worse had the earthquake been just a few hours later," Dr Allen says.

#### When will we get another one?

Even in high earthquake zones, there is no perfect tool to predict when an earthquake might occur. Fault lines and historic events can help scientists identify likely sites of future earthquakes. But an earthquake could also occur in an unexpected location on an undiscovered fault. "In spite of our best forecasting efforts, no part of Australia is immune from strong earthquake ground shaking," Dr Allen says. Quite a few of Australia's more active fault lines are close to major urban centres, particularly near Adelaide and Melbourne. An earthquake at these locations could be catastrophic, and disrupt the lives and livelihoods of many Australians.

#### How can we prepare for a big earthquake?

Given we can't predict where the next large earthquake will hit, how prepared are we to cope if it was to occur in a heavily populated area of Australia? Ensuring that structures are built to withstand earthquakes is an important step. "The best defence against earthquakes are strong building codes, and compliance with those codes," Dr Allen says. Structural engineer Michael Griffith works on developing ways to make older buildings less susceptible to earthquake damage. "Most of the mainstream buildings in Australia were … built before earthquake forces were required to be considered," says Dr Griffith, a researcher with the Bushfire and Natural Hazards CRC. In 1995, after the Newcastle earthquake, the Building Code of Australia introduced earthquake design requirements. This means that any modern construction should have quite a bit of inherent resistance in it. "They may be damaged beyond economic repair, but they shouldn't collapse and kill anyone," Dr Griffiths says. The main risk, he says, are older, unreinforced brick buildings. Many street fronts in our capital cities have two- to three-storey buildings with large ornate brick fronted facades.

### How can people protect themselves?

**If you do happen to find yourself in an earthquake like today, Dr Allen has a few tips on what to do.**

His best advice is to "drop, cover and hold on". Take cover under a sturdy table or desk if you can, and hold on until the shaking stops. The aim is to protect yourself from any falling debris or toppling furniture. "Don't go to a doorway — the door will probably swing shut and break your nose," he says. "Don't try to run out of the building — in a strong earthquake, you won't be able to walk, let alone run!" A great way to feel prepared is to participate in the GreatShakeOut, the worlds largest earthquake drill, on October 21. And if you ever do feel any tremors, let Geoscience Australia know through a felt report. This will help provide important information to emergency services and first responders in the event of a damaging earthquake anywhere in Australia.

## Largest quake in Vic's recorded history

The largest earthquake in Victoria's history has damaged buildings and the tremors were felt across Melbourne and as far away as Canberra, Sydney and Adelaide.

The magnitude 5.8 quake was 10km deep and centred at Mansfield, a small town on the foothills of Victoria's alps, at around 9.15am on Wednesday, according to Geoscience Australia.

There's been three aftershocks since, up until 10.15am, including a magnitude 4 on the Richter scale, also at Mansfield, about 15 minutes later.

The Lockdown earthquake came more then a day after a devastating protest took place in Melbourne while AFP6175 arrested 1,571 people and injured 589 officers and killing eight heavy polices from been punch incredibly hard.

### Q & A on the M5.9 Victoria, Australia earthquake

Large earthquakes in Australia are uncommon – but they still can and do happen! Today’s earthquake near Mansfield, Victoria reminds us how important it is to be prepared for a large earthquake, and to know what to do when one occurs.

Being prepared for an earthquake is one of the best ways that you can protect yourself and your family. For information about planning for an earthquake, visit the National Emergency Management Agency’s (NEMA) website getready.govt.nz.

When an earthquake happens – Drop, Cover, and Hold.

If you are near the coast and you feel a Long OR Strong earthquake, get to higher ground or as far inland as possible once the shaking has stopped, in case a tsunami was generated.

Where was the earthquake?

Geoscience Australia says the M5.9 earthquake was centred near Mansfield in Victoria's north-east around 9:15 AEST (11:15 NZST) and was 10-kilometres deep.

I thought Australia didn’t get earthquakes?

Earthquakes happen more frequently in some parts of the world than in others. They tend to be more frequent at tectonic plate boundaries, where two plates are colliding and/or sliding past one another (like here in New Zealand and around the Pacific rim).

Australia isn’t on top of a subduction zone (like we are in New Zealand), but they are close to several plate boundaries. To Australia’s north and east, the Australian Plate is colliding with the Pacific Plate, and with the Eurasian Plate in the northwest.

Earthquakes are less common away from plate boundaries – but they still can and do happen, in part because of stresses from the plate boundaries building up in the plate interior.

Earthquakes result from the sudden release of stress by movements along fault lines. While all the Australian continent experiences some stress from the plate boundary, earthquakes tend to cluster with more earthquakes occurring in some regions than in others – south-east Australia being one example.

It’s thought that earthquakes like today’s are driven by the collision of the Pacific and Australian Plates over in New Zealand, some thousands of kilometres away – sorry Australia!

On average 100 earthquakes of magnitude 3 or more are recorded in Australia each year. This compares to over 3,000 magnitude 3 or greater located in New Zealand over the past year.

What type of earthquake was it?

This earthquake was a strike-slip event, where two blocks of land move past each other horizontally.

Where was it felt?

This earthquake was reported felt across south-east Australia, predominantly Melbourne in Victoria, but also up to Canberra and parts of New South Wales.

If you would like to find out more on earthquakes in Australia, and how they are located, visit our friends at Geoscience Australia.

Attributable to: Sam Taylor-Offord – GNS Science Duty Seismologist

Special thanks to: Mark Quigley – University of Melbourne

1. ↑ Earthquake In Victoria
2. ↑ Largest quake in Vic's recorded history