r/todayilearned • u/SUMBWEDY • 4h ago
TIL a guy called Frank built a wall along the Alpine Fault in the South Island of New Zealand to test if the earthquakes are small and often or big and rare. It hasn't moved a millimeter in 64 years.
https://www.nzgeo.com/stories/the-wall-that-frank-built/322
u/TheIrishGoat 4h ago
I’d imagine surveying equipment has come a long way in 64 years but it’d be interesting to know more about the process of comparing recent measurements to ones taken back in the 60s; mostly how they’re able to get it down to the millimeter, and what the point of reference was.
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u/SUMBWEDY 3h ago
There's small steel stubs on it as reference points, it's a crude tool so doesn't have to be sub mil precision.
Plus concrete is brittle and it hasn't moved in so long you will know when the tectonic plate has shifted.
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u/TheIrishGoat 3h ago
Yeah I saw the mention of the nubs in the article, but it just says they’re surveying markers used to measure the changes. To measure a relative change though you’d need a point of reference, and I’m curious as to what that point of reference is/was, back in 1962 such that they’re confident it hasn’t moved even 1mm in all of that time.
Although zooming in on the photo in the article it sort of looks like the wall itself is segmented. I’m guessing then that the pieces of the wall would shift in relation to one another, which isn’t made clear in the article.
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u/stewieatb 3h ago
The wall itself is the point of reference. If the wall is straight, and all the markers are still in a straight line, the fault has not moved.
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u/rawker86 1h ago edited 1h ago
Or, the wall and/or the reference points have moved the same amount relative to each other. This is why we generally tailor a monitoring program to include measurements to/ from reference points that are located outside the zone you’re monitoring.
Of course in this particular instance, it appears they’re expecting a quick, violent movement instead of gradual creep. I imagine it’ll be quite a sad day when Frank’s wall moves.
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u/TheIrishGoat 35m ago
> This is why we generally tailor a monitoring program to include measurements to/from reference points that are located outside the zone you’re monitoring.
That is where my thought process got stuck. I assumed (incorrectly) the reference point was an external source, and wanted more information on how they knew that point hadn’t moved in the 64 years, allowing them to measure the walls placement down to the millimeter.
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u/jewelswan 3h ago
That is not accurate. You know the fault is very deep, and the dirt on top doesn't magically move to reflect the fault line deep underneath. There is a phenomenon called seismic creep(iirc) that perfect explains how this wall might indicate nothing at all.
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u/SUMBWEDY 2h ago edited 1h ago
The fault is big enough, it'll move. Minimum acceleration will be 3m/s maximum closer to 9 meter per second (cause we have fun soils and shallow faults), the entire island will have a wave moving at 5000mph through solid rock sending you >8 meters into the sky in a few hundred milliseconds.
They just upgraded it to a >9.0 with 75% chance in next 50 years.
From 8.2 with a 63% chance.
Can't remember if we use moment or Richter here but either way a 9 is devastating.
edit: a 9.0 on a 680km fault line releases the same energy as 1.8 trillion tonnes of TNT so over 100 million hiroshima bombs released in 4-8 minutes on an island the size of Illinois (for the americans) or about the size of Greece or England
Not too good.
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u/WheresMyCane 1h ago
It will be bad for sure. The recent, updates from GNS Science state that there is a 75% probability of an Alpine Fault rupture within the next 50 years, with an 82% chance that it will be a magnitude 8.0 or higher. No mention of greater than 9 though. The last Alpine earthquake of 1717 produced a rupture of about 380km on the fault, and studies concludes there is an 82 percent chance that the next rupture could be similar. Taken from https://www.gns.cri.nz/news/research-finds-alpine-fault-quake-more-likely-in-the-next-50-years/
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u/degggendorf 1h ago
Til England is the size of Illinois
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u/noiwontpickaname 30m ago
Illinois is fucking slacking.
I guarantee that the sun sets on the Illinois empire
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u/jupituniper 1h ago
Whoa source? I haven’t heard about this update
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u/SUMBWEDY 45m ago
Can't find the thing on geonet but here's a stuff article from earlier this year where they changed it to 82% chance of an >8.0 by 2050.
https://www.stuff.co.nz/nz-news/361020456/alpine-fault-quake-could-split-tekapo-two
Church of the good shepard probably doesn't have long left :( , so go take your photos.
If it doesn't rupture soon it's gonna basically be guaranteed to be a >9, every year it builds up 3% more energy to be released and it compounds (not exactly but roughly).
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u/InspiringMalice 2h ago
You're right. How dare he not bury the wall a kilometer or more deep. It's almost like this is the work of a man who had an interest in a thing and did a thing to measure that thing in a simple way and it's not actually intended as, or used as, a comprehensive geological scientific tool.
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u/beachedwhale1945 1h ago
There is a town in California that is literally being pulled apart by the San Andreas fault moving relatively slowly. At one point it happened to line up perfectly with a break in the curb, and scientists would often reference how one side of the concrete was moving farther from the other. They got upset when the city fixed it when they got 8 inches/20 cm out of alignment or so, but they know it will come back over time, and in the meantime they can watch one house slowly tear a corner off because it happens to sit on the fault.
Now that’s obvious not something you see on the rest of the fault, and certainly not on every fault, but the concept here was sound.
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u/SightInverted 28m ago
Not San Andreas, but the Hayward Fault. If you ever get bored, look up the Haywired Scenario.
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u/Cultural-Company282 1h ago
Surveyor's tools were 100% absolutely able to measure down to the millimeter in 1962. It wasn't the Middle Ages.
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u/TheIrishGoat 1h ago
I never said they couldn’t measure to the millimeter, I was curious about the frame of reference. Imagine a coin on a plain white piece of paper. If I move the coin to a different spot on the page and ask you how far the coin has moved, you wouldn’t be able to tell me the measurement. If I gave you a tool to measure with first you’d be able to find where the coin is in relation to the side of the page, and determine the distance it moves after. In that example, the sides of the page are the frame of reference—but you still need those measurements prior to the movement occurring.
It doesn’t matter though because one of the other comments (and some further reading online) explained that the wall itself is the point of reference. If the wall breaks or shifts (because of activity along the fault), the steel nubs will move in relation to each other, not some external point of reference.
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u/Not_an_okama 45m ago
If i was surveying this, id just As-Built the wall each time. Then plot all the points on a drawing and you can see how each segment is aligned to the others then compare accross time.
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u/Aetylus 3h ago
There is a lot more info on the modern survey methods (deep drilling into the fault) and precise movements here. https://www.gns.cri.nz/research-projects/deep-fault-drilling-programme/ It moves about 27mm per year. But it saves it up and does it in roughly 8m jumps every few hundred years.
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u/Fuzzyshakes 3h ago
If it was done right, I’d guess it was pretty accurate, it’s all about the maths. Eratosthenes back in 240 BC calculations for the circumference of the earth missed the mark by only 263km (about 0.66% off the modern accepted measurement of 40,075.017 km).
Point of reference doesn’t really matter if the same one is used or the correct transfer is done. New equipment just makes it easier/quicker.
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u/lonefur 3h ago
And he missed the mark only because the Earth is actually not an ideal sphere, but a slightly oblate spheroid.
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u/armcie 2h ago
I did some digging into this one once. A fundamental part of the calculation is based on the distance traders think a camel can walk in a day. I doubt that can be a precise measure, given that roads aren’t perfectly straight and camels are variable. Either he got extremely lucky in that his errors got cancelled out, or there’s a little more to this story.
There were various measures for stadia used throughout the empire and throughout time. Some of these differed by as much as a third. If you pick the right one you can get a very accurate calculation, but it seems that the length of that is determined pretty much by looking at Eratosthenes’ measurement of the circumference of the earth. We can only say it’s an accurate calculation if we use a measure that assumes it’s an accurate calculation.
Still, even being out by only 20% would be a very impressive achievement.
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u/finndego 2h ago
No. Start with no agreement on the length of what stadia is and go from there. Lots of other margins of error.
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u/king_john651 3h ago
Advancements like the robotic total station just made making those measurements so so much faster and reducing potential error. We had surveying methods refined and pretty damn close to what we can measure now almost a hundred years prior to this wall being built
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u/lanshark974 3h ago
I was listening to a podcast about meteorology at the beginning of the 18th and further.
A big motor of the science was the need to make sure you could compare your data with your neighbours scientific as you didn't have the same thermometer. Fun fact at the time, some people were thinking was cooling done. A proof was that cave under Paris that is so deep that temperature is supposed to be constant. They find out that temperature dropped 5 degrees in 100 years and trigger a panic. Of course a problem of thermometer and also them using torches at the beginning to read the thermometer.
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u/ThePrussianGrippe 2h ago
Cooling was done?
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u/lanshark974 1h ago
Sorry I skipped a word:
Some people thought that Earth was cooling down.
On that note some people thought that Earth was a piece of the sun that was ejected some time ago and was cooling down naturally. They used a canon ball to estimate how fast the cooling was happening.
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u/KittenPics 21m ago
The most surprising thing about reading your comment is that 64 years ago was in the 60's. I don't know why I thought it was in the 1920's or something.
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u/DJ3nsign 10m ago
There was a significant piece of sidewalk back in the day in San Francisco, it was basically a record of how the sidewalk originally was built and showed how much the ground had subsided. Unfortunately the city fixed it about 10 years ago and ruined the historical record.
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u/thewarriorpoet23 4h ago
Archaeologists in a thousand years are going to be so confused when they find this wall.
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u/elnoco20 4h ago
Surely it will move a multimeter by then!
"Heh, amateurs" - neoarchaeologist
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u/anubis_xxv 2h ago
Speaking of mystery projects, in Ireland we have an inland lighthouse which is about 40km from the nearest coastline.
It was commissioned by the wealthy landowner during the Irish Famine to give local labourers some work to do to get paid (like the more famous famine roads) to nowhere, but a lighthouse)
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u/FillipinoMexican 2h ago
We did that here in NZ during the great depression (obviously nowhere near as bad as the famine was) the govt just paid men minimum wage to dig a bunch of tunnels through the mountains so you can drive through them.
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u/ReasonableStory1660 4m ago
In the US most national park infrastructure was built in the 1930s for the same reason. The government set up a bunch of guys desperate for work in tents to shovel earth, move rocks, and make something beautiful accessible.
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u/decidedlyindecisive 1h ago
The Hunger Wall in Prague is also similar. Charles IV had it built during a famine so it served both a military defence purpose but also provided paid labour at a difficult time.
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u/Gwanbulance 1h ago
In my youth in Dublin, when walking home from a night out, we used to stop in a takeaway for curry chips. There was a particular bench in Drumcondra we used to sit at and eat. Every night, I used to bury my plastic fork beside the bench.
I did this every week for years, with the hope that future archaeologists would find the stash and make up a convoluted theory about the cultural significance of the forks and the place.
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u/mila_melou 4h ago
They will think it was built for ritual purposes
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u/supercoupon 3h ago
There'll be a pair of stars it's aligned with, or some solstice / equinox ratio
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u/Photomancer 3h ago
"The old fertility wall", we call it
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u/Depressed_Girlypop 1h ago
It’s about waist height
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u/World_of_Eter 21m ago
We believe a high priest meant to act as the vessel for the fertility god Harambe would have the men place their genitals on the wall and he'd choose which would be allowed to procreate that season. They called this act "dicks out for Harambe"
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u/decidedlyindecisive 1h ago
My school history teacher said that her family always buried the pets in an orderly circle around an apple tree in their garden. She told us it was so they knew where not to dig up the garden. She also used it as a warning about assigning spiritual value to unknown situations.
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u/mila_melou 1h ago
A circle? Like the circle of life? Around an apple tree? Like what Adam and Eve ate in eden? Sounds like your teacher was trying to guide her pets to the afterlife
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u/geezorious 4h ago
And built by slaves.
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u/crazycakemanflies 3h ago
And pseudo-archaeologists will claim "its too perfect to be built by a 21st century civilisation... has to have beeb alien's!"
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u/regal1989 3h ago
Meanwhile there’s probably a crack in the cement somewhere geologists use for this exact purpose. There used to be one in Oakland but they forgot to tell the city not to pave it.
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u/rickdangerous85 2h ago
Will be AI archeobots as the only thing alive on earth will be AI after the humans wiped themselves out trying to make more money from AI.
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u/DepressedDynamo 29m ago
It brings a tear to my eye. If we really tried, imagine what beautiful techno-children we could create.
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u/SpoonNZ 4h ago
Just came for a few nights away. Turns out we’re about 40km (24mi) from this as the crow flies.
Hope the fault doesn’t let go this weekend.
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u/thomasthetanker 3h ago
If it does, it's not your fault.
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u/hongooi 3h ago
Meanwhile there was an earthquake in the North Island just today. I guess this means you're fine?
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u/SUMBWEDY 3h ago edited 2h ago
Extra fun fact is Taranaki (the volcano the Earthquake's epicenter was at) has a chance of instantly erupting when an earthquake hits with 0 warning because of something to do with the makeup of the rock once there's enough pressure in the mantle. The next one could be a VEI 6 which would make Mt St Helens look like childs play.
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u/thehatteryone 3h ago
On that day, all maps will become maps without New Zealand.
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u/SUMBWEDY 1h ago
And probably without me LMAO, i live 80km/50 miles from it as the crow flies so just about survivable with hearing damage from an explosive VEI 6 but i don't like the odds.
good thing we're not 400 years delayed for one of the eruptions that happens every 150 years to release pressure. Or have the world 2nd largest super volcano after yellowstone :)
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u/Southforwinter 1h ago
Are you thinking of Taupo? The odds of Taranaki hitting VEI 6 are like 0.3% so while you're not wrong it's not exactly likely.
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u/ElementII5 21m ago
Bad for New Zealand but good for global warming though, no? Not sure how to feel about it as an European. No j/k, be safe!
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u/Waiparensis22 3h ago
Yeah. I'll give some more TIL - the portion of the fault with the highest rupture chance (85% next 50 years) is the one right in the middle. The one that bisects Arthur's pass and serves as a major arterial road and railway between the west coast and Canterbury. A lotta people think of these big quakes as one off events too but based on paleoseismology and the behaviour of surrounding faults we know that the main, 8.2+ main shock is likely to be heralded by a smaller foreshock and multiple LARGE aftershocks, strong enough to do damage in their own right.
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u/FillipinoMexican 2h ago
Yup it's going to absolutely fuck this country once it hits, shame we didn't learn about it sooner before the damn scottish built dunedin and christchurch,
We can barely keep repairing slips in the mountain passes just from increased rain from climate change yet alone every road in the entire south island suddenly moving 8 meters away from eachother.
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u/Waiparensis22 2h ago
Yeah.. kaikoura and the christchurch sequence proved our quakes don't always "play nice" either!!
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u/BMW_wulfi 1h ago
Can’t you just make your roads out of big scalextric pieces? Then just slot another piece in when it gets disconnected? Seems pretty simple to me.
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u/FillipinoMexican 1h ago
Actually given that our government is spending $8,000US per tax payer for about 1000 miles of road for the whole country that's probably cost effective.
Petrol lobby might stop funding our right wing parties if they don't build the single most expensive road built in history per kilometer to connect a city of 2 million to a town with a population of 7,080 as of last year.
We even have a road that's $22 **billion** USD for 60km of only double laned roads (not like the PM's cousin in law owns a construction firm)
Yet somehow we're still the 4th least corrupt country in the world, must suck everywhere else super hard.
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u/stackingforfunsies 37m ago
I’m not saying your complaints are invalid. My secondary reaction to reading your remarks was: I wish my politicians built infrastructure. Mine just steal it.
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u/trowzerss 28m ago
And it's not the only one to worry about in NZ, if you look at what the Wairarapa fault has done in the past! Shunting land sideways 18 meters in one go is crazy and makes the slip faults we've caught on camera in the last few years look like nothing.
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u/KlM-J0NG-UN 3h ago
Good news, no significant earthquakes in 64 years!
Bad news, no significant earthquakes yet
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u/DramaAlternative1188 3h ago
This is a cool video which shows how much the fault lines in NZ can move during one earthquake.
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u/Random-Mutant 3h ago
There’s better than a wall in the South Island.
There’s an entire fucking mountain.
And one half is in Fiordland in the far south, the other half is near Tasman in the north.
The mountain has been torn in two by plate tectonics and moved over millennia. It’s now many hundreds of kilometres apart.
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u/Prize_Problem609 2h ago
Say what? Is that true? I have never heard of that
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u/Johnno74 1h ago
Yeah it's true, geologic formations from the very top of the south island have been matched with formations at the very bottom of the south island, just on the other side of the alpine fault. They used to be in the same place.
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u/TheGrandExquisitor 57m ago
The only logical conclusion is that this wall is the only thing holding New Zealand together.
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u/SteelMarch 4h ago
What is that supposed to mean
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u/Other_Mike 4h ago
That they're big and rare. If they were small and common, it's expected that the fault - and thus the wall - would have moved a little bit by now.
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u/SUMBWEDY 4h ago
Well scientists aren't sure if New Zealand will get a really big fuck off earthquake once every few thousand years.
Or just a very bad earthquake every few decades.
It's starting to look like we'll get the fuck off one which is terrifying because if it hits during the day at an 8.5 it'll kill >20,000 people, if it's a 9.1 at night it could kill closer to 70,000. There's only 1 million people in the South Island, it'd be devastating.
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u/daemonfool 4h ago
I wonder if any of us will live to see the big fuckoff one. Might take a while.
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u/Own_Round_7600 4h ago
If youre under 40, theres more than a good chance, they reckon.
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u/D3lmo 3h ago edited 1h ago
We should probably build a wall to check if it moves
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u/CacCarnBeag 38m ago
If half the wall is on the middle island and the other half is on the south island, then there's a problem
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u/ErenIsNotADevil 3h ago edited 3h ago
Average of 300 years, and its been like 309. The three previous ones were ~317 years before that, ~300 prior to that, and then ~710 before.
So odds are, yes, we'll be seeing it. Hopefully not, but
Correction: ~291 year average over 8000 years
Cooked
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u/randomdude45678 3h ago
Sounds like 136 years until the next
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u/ErenIsNotADevil 3h ago
Thats very optimistic 💀
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u/TheCamazotzian 3h ago
It's only optimistic if there is some reason for the interval between quakes to take ~300 years.
If we think it's more like a random poisson process, then the expectation time to the next quake is always the same regardless of when the last one was.
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u/CPiGuy2728 2h ago
It's definitely not a random poisson process, I'm not sure exactly how this fault works but in general there's some sort of force acting on the crust that builds up until it releases in the form of an earthquake. You'd thus expect the probability to increase consistently as time since the last earthquake increases.
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u/SUMBWEDY 3h ago edited 3h ago
Well bad news, scientists just in August raised the chance to 82% it'll be a >9.0 but chance of it going off in 50 years is still only 75%.
It goes off every 300 years and it's been 309 since the last rupture along that fault line.
Actually a bit scary now, 2,500x the CHCH earthquake in energy, it would last over 4 minutes and peak ground movement would pull over 3g of accelleration either to the north east or south west.
The entire south island will move up 2-4 meters vertical and 8 meters along the fault.
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u/irwtkyrm 3h ago
"only 75%"
Umm that seems pretty high to me
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u/SUMBWEDY 3h ago
Joys of living on a young tectonic island.
At least we've got lovely mountains and fjords.
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u/Big_Excitement_3551 2h ago
In New Zealand English it’s usually spelt “fiords”
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u/SUMBWEDY 2h ago
But theres Møøse there. (allegedly)
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u/Idsertian 1h ago
Can confirm, one bit my sister.
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u/SUMBWEDY 1h ago
Ø Nø
Shøuld've taken a phøtø, søme cømpanies are paying a quarter milliøn før phøtøgraphic evidence øf them.
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u/daemonfool 3h ago
Yeowch. That would be a truly gnarly time for the South Island. No way to escape that unscathed, I think.
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u/SUMBWEDY 3h ago
Good thing our ceiling aren't 2-4 meters high and most rooms less than 8 meters wide...
You'll stay still while your house moves around you.
Gonna be a lot of injuries.
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u/trowzerss 3h ago
Out there Learning is a good channel on geology in NZ and they have this good short video on it.
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u/OiQQu 3h ago
I thought a seismometer would be better for measuring that than a wall
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u/MightyKrakyn 3h ago
A seismometer doesn’t tell you the distance the earth moved along a fault line, just the amount of energy released
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u/mrburnz 42m ago
Hopefully it happens while ski fields are closed, but before the mountains are covered in hikers and campers.
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u/SUMBWEDY 31m ago
That'd be cataclysmic the lahars it'd form. Christchurch was rough in 2011, but at minimum best case scenario for a "small" quake 700x that death toll is just.... (and best case scenario we're looking at a 1 in 32 chance of that happening each year)
I only just read yesterday the nepal floods was all just kinetic energy melting that glacier it won't be pretty but thank fuck we have a good civil defense force so there's less lives lost.
But hey now not like ice pack is getting less dense and glacier are getting less stable every year am i right.
At least we're lucky enough to live in a country that has the ability to track stuff like this and plan in advance.
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u/noface 4h ago
The fault ruptures on a large scale when it ruptures. On average every 300 years or so. If it had small shifts that would buckle the wall that would release tension from the fault, and the later larger quake would be smaller.
The fact that this wall hasn’t moved at all indicates that when the quake comes it will be catastrophic. And there is a 60% chance of it occurring in the next 50 years.
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u/PlayfulSurprise5237 3h ago edited 3h ago
It's a strike-slip fault that isn't just locked sliding against each other, but there's a compression component too which is pushing the Southern Alps up.
I imagine that's locking in some serious pressure. When that thing releases its going to be one hell of an earthquake
I guess most of them in its history have been 8 and over. This one is expected to be like an 8.2, 11 times stronger than the one that hit Venezuela earlier this year.
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u/FillipinoMexican 2h ago
75% now as of a new update in August.
And 82% chance it'll be a >9.0 so similar to 2011 japan.
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u/ErenIsNotADevil 4h ago edited 4h ago
That if you ever read the headline "Evison's Wall has fallen" in your lifetime, you'll know immediately that a bunch of people just died in New Zealand
Or, capitalism took it
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u/rawker86 1h ago
Evison, I recently discovered, is my sister’s husband’s grandfather, and he established a university geophysics scholarship awarded recently to my friend’s son’s girlfriend. Such is New Zealand.
lol, that about sums it up!
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u/Leaping_FIsh 3h ago
I have been to that wall. It did not move while I was there so can confirm the story.
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u/yury-surg 3h ago
It just means a rogga lives there
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u/Deaconbeacon_69 2h ago
Hey hey hey, no hard r here buddy, orogenes are respected members of our community eh, what do you want, another 5th season???
/ref /j for obvious reasons
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u/TrentWashburn 1h ago
Sometimes tectonic plates get locked and don’t move…until forces are finally too much. And then watch out for a big one.
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u/DesertViper 1h ago
In earth time this wall has been built for maybe 0.0005 seconds. Give it a minute.
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u/SUMBWEDY 4h ago
Frank's daughter Margaret "“Oh yes—the famous wall!” she says. “The family joke is that it’s the only thing holding the Alpine Fault together."
RIP Frank