5 ms·

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 Eurasia

by Khaine 5y ago

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.

hilbert42 5y ago
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.
- CommieBobDole 5y ago
  Maybe the 1961 NSW earthquake? Though that one was on a Monday morning. https://en.wikipedia.org/wiki/1961_New_South_Wales_earthquake https://en.wikipedia.org/wiki/1961_New_South_Wales_earthquak... Wikipedia has a whole list of significant Australian earthquakes, if that's not it. https://en.wikipedia.org/wiki/List_of_earthquakes_in_Australia https://en.wikipedia.org/wiki/List_of_earthquakes_in_Austral...
  - hilbert42 5y ago
    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.
user123456780 5y ago
I don't know why but I really thought Australia was the most stable continent in the world (I guess thanks Education Queensland). I have lived here my whole life and never experienced an Earthquake.
- simondotau 5y ago
  Your education didn't fail you. Australia is an incredibly stable land mass because it sits in the centre of a single plate.
- senectus1 5y ago
  its is... very very stable. those are facts but they're not really in context.
- thisrod 5y ago
  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.
baggy_trough 5y ago
Strange it's so flat then.
dustintrex 5y ago
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.
- bhrgunatha 5y ago
  > M9 is 1000x more powerful than M6 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. [1] https://en.wikipedia.org/wiki/Moment_magnitude https://en.wikipedia.org/wiki/Moment_magnitude [2] https://en.wikipedia.org/wiki/Moment_magnitude#Definition https://en.wikipedia.org/wiki/Moment_magnitude#Definition
  - chrismorgan 5y ago
    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. https://en.wikipedia.org/wiki/Richter_magnitude_scale https://en.wikipedia.org/wiki/Richter_magnitude_scale: > 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]
    - zamfi 5y ago
      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.
gHosts 5y ago
Feels like some more detail is needed somewhere... sounds sort like "The Australian Dollar is the fastest moving currency"... ...that might be so, but moving relative to what?
- megablast 5y ago
  Than other plates.
  - gHosts 5y ago
    Which one? A bundle of Plates? What about Plates that are 90 degrees to it?
jiggawatts 5y ago
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. See: https://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/datums-projections/gda2020 https://www.ga.gov.au/scientific-topics/positioning-navigati...
- chrismorgan 5y ago
  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.)

by Khaine 5y ago

hilbert42 5y ago

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.

CommieBobDole 5y ago
Maybe the 1961 NSW earthquake? Though that one was on a Monday morning. https://en.wikipedia.org/wiki/1961_New_South_Wales_earthquake https://en.wikipedia.org/wiki/1961_New_South_Wales_earthquak... Wikipedia has a whole list of significant Australian earthquakes, if that's not it. https://en.wikipedia.org/wiki/List_of_earthquakes_in_Australia https://en.wikipedia.org/wiki/List_of_earthquakes_in_Austral...
- hilbert42 5y ago
  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.

user123456780 5y ago

I don't know why but I really thought Australia was the most stable continent in the world (I guess thanks Education Queensland). I have lived here my whole life and never experienced an Earthquake.

simondotau 5y ago
Your education didn't fail you. Australia is an incredibly stable land mass because it sits in the centre of a single plate.
senectus1 5y ago
its is... very very stable. those are facts but they're not really in context.
thisrod 5y ago
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.

baggy_trough 5y ago

Strange it's so flat then.

dustintrex 5y ago

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.

bhrgunatha 5y ago
> M9 is 1000x more powerful than M6 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. [1] https://en.wikipedia.org/wiki/Moment_magnitude https://en.wikipedia.org/wiki/Moment_magnitude [2] https://en.wikipedia.org/wiki/Moment_magnitude#Definition https://en.wikipedia.org/wiki/Moment_magnitude#Definition
- chrismorgan 5y ago
  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. https://en.wikipedia.org/wiki/Richter_magnitude_scale https://en.wikipedia.org/wiki/Richter_magnitude_scale: > 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]
  - zamfi 5y ago
    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.

gHosts 5y ago

Feels like some more detail is needed somewhere... sounds sort like "The Australian Dollar is the fastest moving currency"... ...that might be so, but moving relative to what?

megablast 5y ago
Than other plates.
- gHosts 5y ago
  Which one? A bundle of Plates? What about Plates that are 90 degrees to it?

jiggawatts 5y ago

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. See: https://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/datums-projections/gda2020 https://www.ga.gov.au/scientific-topics/positioning-navigati...

chrismorgan 5y ago
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.)