The Australian plate is the fastest moving continental land mass on Earth and is colliding into the Pacific plate to Australia's north and east, and the Eurasian Plate to the northwest. This generates mainly compressive stress in the interior of the Australian continent, which is slowly building up across the plate as it moves northeast about 7 cm per year. Australia's earthquakes are caused by the sudden release of this stress when rocks deep underground break and move along a fault line. While some parts of the country are more likely to experience earthquakes than others, large earthquakes can occur anywhere across the continent, and without warning.
On average 100 earthquakes of magnitude 3 or more are recorded in Australia each year. Earthquakes above magnitude 5.0, such as the destructive 1989 Newcastle earthquake, occur on average every one-to-two years. About every ten years Australia experiences a potentially damaging earthquake of magnitude 6.0 or more such as the magnitude 6.5 Meckering earthquake in October 1968.
A "fun" side effect of this rapid movement rate is that Australia drifts noticeably relative to GPS-based coordinates. Many programmers made the lazy assumption that coordinates remain fixed and don't need to be adjusted based on the current date.
The effect of this is that the maps in my car are already out by several meters. It's sufficiently bad that it'll sometimes jump to a different road.
Geoscience Australia developed the new "Geocentric Datum of Australia 2020" (GDA2020) to fix this, but not a lot of software has been updated with it as of 2021.
Several metres is a slight exaggeration, not enough to matter for such purposes anyway, and may even already be taken into account.
From 1994 to 2020, the physical difference was about 1.8m (that’s comparing it with another map projection, but what else can you do?), so in what should be the worst case scenario (if they were actually using accurate maps which I think would reasonably imply nothing worse than GDA94), you should have less than two metres of drift, and the only time that’s ever going to matter is when you want to identify service roads distinctly from the adjacent main road. And continental drift is probably still even within your car’s GPS sensor’s margin of error. No, I don’t think you can reasonably blame continental drift for road jumping; it’s typically going to be bad map data, with roads simply being marked in the wrong place. I have a 2010 Mazda 3 with maps from 2010, and out in the country its maps are commonly out by 10–20 metres, with the largest deviation I’ve observed where I know the route hasn’t changed in at least the last couple of decades being about 150m.
To my mind, the real doozy about these geodetic datums is that they’re time-dependent, including a prediction of continental drift. I have no idea whether the car’s maps system does do that, but it should be doing something like storing all coordinates in GDA94, rendering in MGA94, and projecting GPS coordinates into that coordinate space, so that continental drift’s effects are negligible.
(I’ve wondered casually about continental drift in map projections before, but never gotten round to investigating the reality of it. I didn’t realise they could be time-dependent until today. I must get round to asking my dad about it, as he’s done quite a lot of maps and projections stuff.)
The main issue is for navigation that supports lane-level precision. The 2m drift is still not enough by itself, but there is a base error of a meter or two in the GPS signal itself. So the two together is enough to confuse the navigation and have it show you driving in an adjacent lane, which then gives you bad directions.
From memory the opening of a military technology to the general public forbid using it to this level of accuracy? Maybe it was only sub metre accuracy?
During the 1990s, GPS quality was degraded by the United States government in a program called "Selective Availability"; this was discontinued on May 1, 2000 by a law signed by President Bill Clinton.
GPS can get extreme precision as in mm when given a long tine and a fixed location, which is mostly useful for geologists. However, you can get close to that using extreme precision accelerometers and GPS, but it’s rarely worth the cost.
A rough guide: The GPS signal works on two codes: coarse acquisition (C/A) and precision (P) codes. The P codes are 1 week long and require a secret key even to this day. C/A is I think a few hundred milliseconds and easily locked onto.
They used to use C/A for what it says: coarse acquisition of where you are (space and time), to work out where you are in the P code signal to start looking. Apparently a difficult problem without the C/A to start you in the right place.
To stop baddies using GPS for anything evil, the C/A had an error built in. This error in C/A is what Bill Clinton removed.
To this day military still can use P codes and it is still possible for the C/A to go out to lunch. But practically this is unlikely to happen given the amount of civil applications dependent on accurate gps.
With all due respect, you're making that sound a lot worse than it is when compared to places that are genuinely earthquake-prone. Australia is extraordinarily stable in geological terms and well outside the Pacific Ring of Fire, which frequently generates earthquakes of magnitude 9+. And since the magnitude scale is logarithmic, M9 is 1000x more powerful than M6.
Yes, magnitude does not equal seismic intensity and all that, but Australia has never in recorded history experienced a M7+ earthquake, while Japan alone experiences one every couple of years and New Zealand has had 4 in the last 5 years.
I assume you're using moment magnitude [1] since it's the most common measure. In fact every 2 integers is a 1000 times increase [2] so M8 is 1000 times more powerful than M6.
Whoa, whoa, ⅔ log₁₀? I learned the Richter scale which is log₁₀ and didn’t realise that wasn’t what was used any more, and I’m pretty sure that’s a normal misconception.
> Because of various shortcomings of the ML scale, most seismological authorities now use other scales, such as the moment magnitude scale (Mw), to report earthquake magnitudes, but much of the news media still refers to these as “Richter” magnitudes. All magnitude scales retain the logarithmic character of the original and are scaled to have roughly comparable numeric values (typically in the middle of the scale).[citation needed]
Not to nit, but Richter is also not just log_10: a single point increase is ~32x more energy. This is due to the relationship between energy and shaking amplitude:
> The energy release of an earthquake,[27] which closely correlates to its destructive power, scales with the 3⁄2 power of the shaking amplitude[why?]. Thus, a difference in magnitude of 1.0 is equivalent to a factor of 31.6 in the energy released.[28] The elastic energy radiated is best derived from an integration of the radiated spectrum, but an estimate can be based on mb because most energy is carried by the high frequency waves.
Dropping constant factor does not seem that important to be honest. The important thing to be exposed to/take away was the logarithmic behaviour. I'm sure if you want to go be a seismologist you will quickly learn all the details. If people realise the magnitudes are exponentially more damaging , then isn't that sufficient for the general audience?
Australia is really stable. The edges of the Australian plate are in New Zealand and Java, which aren't. But tectonic plates are big, and we're in the middle.
With those facts, I'm surprised that we don't have larger quakes. I remember the Newcastle one, my parents' home had its roof damaged in it. I also recall a rather strong one in the Blue Mountains when I was a kid but can't remember exactly when it was (sometime in the early to mid 1960s if I recall correctly). I think is was on a Saturday in the AM, and I definitely do recall having difficulty walking across my bedroom whilst it was occurring.
Ha, right, thanks for that. It must have been the Monday as that's around the date as best I can remember and the time in the morning seems right too (it's been a while now and the grey cells are loaded with superfluous junk). ;-)
At the time the quake began I was still in bed (being a Monday I should have been up a getting ready for school - perhaps it was school holidays and that's why I thought it was a Saturday, I must check that up later).
I'm almost certain that I was asleep when it started and it woke me up (more evidence for school hollidays?). Initially I was confused and wondered where the almighty noise and rattling-type vibrations were coming from. My first reaction was that it was a jackhammer and the Council was digging up the street (an all too common occurrence as the asbestos cement water pipes broke frequently (yes, you read correctly, they were asbestos) - but all the noise and action seemed too localized to be in the street. I immediately jumped out of bed and tried to run across the bedroom (a very large room that I shared with my brother) and traversing the room was a bit of a task as my feet were slipping from under me. Even though I'd never experienced an earthquake previously it was immediately obvious to me what was going on by the time I was about one half meters from my bed. Being a techie even back then, as soon as I'd figured it out I stopped and watched everything that was happening - 'roof' dirt coming down from the cornice after it had separated from the wall, the clothes cupboard door rattling like crazy and the floor boards bouncing to the extent that it was difficult to walk (but standing still was OK).
I wasn't the slightest bit scared even the moment when I realized what was happening, if anything I had a kid's excitement of a new experience. I didn't try to escape out of the room either (methinks not a good move in hindsight), I simply watched from the center of my room until it was over. It's hard to be accurate about the quake's duration but I'd guess it was about 30 second, perhaps even 40 but that's unlikely as time dilates in circumstances like that. .
From the docs, I reckon I was about 90km from the epicenter. Similarly, the Wiki list of quakes is fascinating, I never realized there were that many.
I've never thought to look up the details previously as it hasn't been in the forefront of my mind until now. It's been an interesting experience down memory lane.
I think there's some important context here for people reading this from overseas, geologically Australia is extremely stable as its far from any tectonic plate borders and there's very few large earthquakes here. This quake is one of the largest to happen here. Many people here have never experienced the sort of whole building shaking type of experience we just had.
Have a look at some maps of plate tectonics. The huge Australian plate collides with the Sunda plate along a boundary which is much closer to Indonesian landmasses compared to the Australian ones.
Felt this as far away as Wagga Wagga, NSW. It's insane how far these things travel, and especially a shock in a place like Australia where Geological activity is so low. We're just not used to this kind of thing
Never knew how far earthquakes travelled. I guess everyone else on the planet knows but I didn't realise you could feel them in a different state until today. And this wasn't even a big one compared to what they get all the time in places like NZ or Japan. Nature is awesome.
I work for a Kiwi company and many of my colleagues are Kiwis. When I posted this on company messaging platform, many of them were surprised that Australia gets earthquakes too. I felt quite strong tremors here in Ringwood, Vic. Wife and I ran out through the backdoor to the garden. It was quite an experience.
> Wife and I ran out through the backdoor to the garden
For future reference, during an earthquake if you’re inside it’s usually far safer to climb under a desk or table, stand in a doorway or up against a wall in the center of your house rather than going outside. Falling trees, power lines, broken gas mains, and even soil liquefaction can be very dangerous.
I live 2M above sea level and 100M from the pacific ocean in New Zealand, the last two biggies I was out of my home and 10KM down the road before the aftershocks finished.. Tsunamis can also be pretty dangerous :-)
Thanks for that and you're right. I read that on the SEC website. But, my garden has a good amount of space and has small trees. Far from powerlines. Whereas the house is probably 50 to 60 year old wooden structure built on a sloped block, which trembled quite badly! hahaha. so decided to run with the wifey!
>For future reference, during an earthquake if you’re inside it’s usually far safer to climb under a desk or table, stand in a doorway or up against a wall in the center of your house rather than going outside. Falling trees, power lines, broken gas mains, and even soil liquefaction can be very dangerous.
I absolutely loathe statements like yours that masquerade as helpful advice but are nothing more than a crude rule of thumb fundamentally built on an assumption of everyone being stupid. People aren't stupid. They're mostly about as smart as you are.
People don't run outside during an earthquake simply to be outside. They run outside to be free of stuff that might fall on them. Away from falling things is the end goal, being outside is not the end goal, it's just usually the first step. Sure, someone once upon a time probably ran outside and got hit with a tree or power line, I'll give you that. But the overwhelming majority of people are going to run outside to a location where there isn't stuff that has the potential to fall on them because that is the goal, to get away from stuff that might fall on them. If the power lines and trees are swinging around they'll get away from them. People who do not have such a place readily available will dive under a table or something.
If you think the building or portions thereof might collapse, by all means get the F out of it.
You're adding emotion to my statements where there is none.
> I'm sure he/she wrote that with the best intention.
I agree. But if you throw a cigarette butt out the window with good intentions it's still littering.
>Hope you're okay!
Sarcasm conveys poorly over test. Next time just say "yikes" and save yourself the typing and everyone else the reading. People less fluent in English will appreciate it too.
> You're adding emotion to my statements where there is none.
With the noblest of attempts here, take a moment to read your comment again and take a breath. There's a lot of emotion here that might be escaping you.
I'm just down the road in Croydon and it was much the same. Thought the retaining wall outside had busted open and I was about to lose my house, didn't even occur to me it might be an earthquake
I thought it was some possums mucking around on the roof. My wife thought I'd started exercising on the wooden floorboards! Hope you and your family are safe.
Yes, I'm in the outer south-eastern suburbs of Melbourne and everyone in our household were standing in doorways. This is certainly the largest and longest one I've experienced, and I've lived in Papua New Guinea and Tokyo for short-ish periods of time.
> many of them were surprised that Australia gets earthquakes too.
While we do, ones that are widely noticeable let-alone alarming are quite rare.
Like most of the earthquakes I felt in the bay area, I spent most of it thinking it was an unbalanced dryer in the final stages of its cycle.
It roughly felt equivalent to the 2014 Napa Quake (which was also a 6). For normally geologically-quiet Melbourne, however, this would be the strongest quake ever recorded.
I was cooking pancake before my stand up meeting, then the floor was just shuffling at the apartment. Everyone ran off outside the building. It was pretty frightening for first time feeling, apparently the affected areas spread out so far from west to eastern suburbs.
> Although the strongest earthquake I've ever experienced was in Indiana.
That is…unexpected. I’ve felt two here in Indiana in 50 years, neither of which were all that notable other than the fact that we almost never get them.
Looks far enough away to not have caused anything too serious in Melbourne. Is there anything much closer to the epicenter there that would be harder hit?
The few early news articles I can find seem to confirm not much serious damage in Melbourne.
Not much damage in Melbourne, at least so far (hopefully nothing bigger happens, this comment is a couple of hours since the main shock). A few poorly built brick walls have toppled in some places but that's about all.
The epicentres were close to Mansfield[1] which is a town of about 4,800. According to State Emergency Services (SES) reports in the news, they've had a bit over 100 requests for assistance, largely related to minor structural damage to chimneys and facades of buildings.
If you search twitter for "Chapel Street" you can probably find some footage of a wall collapse.
Nothing too serious all in all as far as I can tell. No reports of injuries that I've heard.
While there are plenty of small tremors in Australia that usually go unnoticed, ones that are widely noticeable let-alone alarming are quite rare.
There are some towns nearby. Worst I've heard of so far is broken windows, cracked ceilings and the like. Definitely some potential for injury, but I haven't heard of anyone significantly hurt.
We don't get big ones with high frequency as we are not on a tectonic boundary. No active volcanoes either.
There are faults and stresses within the continental plate but they mainly produce smaller earthquakes with lower frequency but they do happen. Given the population density people rarely feel them. So even a moderate quake is a huge novelty. I can understand why people are so excited and sharing it on social media. I am probably about 700km away and I only barely felt it and it might be the only earthquake I feel in my entire life.
I grew up with an anecdote along the lines of that in the 60s or 70s there’d been one of the biggest earthquakes ever recorded in Australia, and the total property damage had been that one cow shed fell over, because that’s how empty much of Western Australia or Northern Territory is. The anecdote may be slightly exaggerated for comedic effect, but it’s also probably not far off the truth.
Melbournians who left their homes for fear of the roof collapsing were jailed for breaking quarantine. Premier Daniel Andrews stated: "Trying to survive a natural disaster is no reason to spread COVID. You will all be punished." (note: this comment is satire)
Pieces of roof falling on your head from a 5.9 Richter Scale earthquake is not "an emergency". It is actually a sign of White Privilege, since only White People are rich enough to have places with roofs.
More importantly, I am worried your comment has breached the Victorian Standards of Acceptable Speech (VSAS). "This is poor satire" - expressing your own opinions is strictly forbidden and is punishable by years in hard labour camps or by firing squad. Though this sounds extreme, it's really for the safety of the people, to protect them from dangerous thoughts. Please be careful about what things you share online.
I would have thought that you'd find my comment appropriate, given that Melbourne is now starting to display policies similar to those of China. This is not just empty rhetoric - they are instituting laws that you of all people should find worrisome. Wait... you didn't specify if you support the CCP or support an independent and free Hong Kong, so maybe the opposite is actually true.
On average 100 earthquakes of magnitude 3 or more are recorded in Australia each year. Earthquakes above magnitude 5.0, such as the destructive 1989 Newcastle earthquake, occur on average every one-to-two years. About every ten years Australia experiences a potentially damaging earthquake of magnitude 6.0 or more such as the magnitude 6.5 Meckering earthquake in October 1968.