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Earthquake in Japan yesterday may have shifted land 1.3 meters

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Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#31

Post by IKantRead »

sandworm101 wrote: post #2

The amount of energy released in such events boggles the mind. Shifting cubic-kilometers of rock, in this case several hundred or even thousands of cubic-kilometers, even a few inches requires more energy than all the worlds nukes many times over. We live atop an immense heat engine, every little vibration of which could power our entire civilization for years.

I've always found it fascinating that geophysicist and earlier advocate for Bayesian methods, Sir Harold Jeffreys, didn't believe in continental drift and plate tectonics because he felt there was no known source of energy on the Earth massive enough to explain this movement. [0]

He remained an opponent until death (at which point continental drift was widely accepted) which is both a testament to the literally unbelievable energy behind seismic activity and the importance of updating your Bayesian priors as you gain new information.

0. https://en.wikipedia.org/wiki/Harold_Jeffreys#Opposition_to_...

Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#32

Post by Retric »

amluto wrote: post #27
badcppdev wrote: post #4

This is a very sad example of land movement and it's a tragedy that people have died in the aftermath and recovery effort. But it's also an important reminder that our super accurate GPS measurements are not 100% reliable over time. The earth moves. Either in jumps like this or fairly constantly if it's somewhere like Australia [0] 0 - https://www.nytimes.com/2016/09/24/world/what-in-the-world/a...

> But it's also an important reminder that our super accurate GPS measurements are not 100% reliable over time. The earth moves. This is IMO an odd statement. Land moves, and we can measure that movement extremely precisely. If software was more competent, we would record positions in four dimensions: space and time, relative to a well defined coordinate system. And we could map a position at one time to a position a…

It’s not just a software problem, you also need to know how the earth is being deformed which is far more difficult than you might think.

Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#33

Post by KeplerBoy »

samstave wrote: post #28
KeplerBoy wrote: post #24

Earlier quoted context omitted.

How is this solved? The surface of the earth just shifted in a highly non-linear and non-uniform way. Places are not at the same coordinates or at the same distances from each other they were last week.

Read the link. The quantum magnetic locator doesnt use GPS satellites, so the "our GPS is not 100% accurate" is solved by the magnetic quantum thing... its just not available on _ your _ smartphone. Re-read my post, I believe that the real use of Lockheeds Quantum GPS is for subterranian and submarine navigation more than it is for aircraft - hoever, if we can map the magnetosphere of other planets, say, mars, then t…

But the problem is not the accuracy, it's the temporal stability. GPS is accurate enough, but it's no good if the physical locations shift over time.

Most people need an up-to-date map, not just a location on a map.

Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#34

Post by chrismorgan »

amluto wrote: post #27
badcppdev wrote: post #4

This is a very sad example of land movement and it's a tragedy that people have died in the aftermath and recovery effort. But it's also an important reminder that our super accurate GPS measurements are not 100% reliable over time. The earth moves. Either in jumps like this or fairly constantly if it's somewhere like Australia [0] 0 - https://www.nytimes.com/2016/09/24/world/what-in-the-world/a...

> But it's also an important reminder that our super accurate GPS measurements are not 100% reliable over time. The earth moves. This is IMO an odd statement. Land moves, and we can measure that movement extremely precisely. If software was more competent, we would record positions in four dimensions: space and time, relative to a well defined coordinate system. And we could map a position at one time to a position a…

This is how things are done. You specify the datum, coordinates, and time. Geodetic datums are time-dependent transformation functions. Any software that is recording points at the particular time called “now” and not either recording the coordinates and time, or reprojecting them to a meaningful reference datum at its epoch (origin in time), is bad.

Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#35

Post by arghwhat »

Retric wrote: post #32
amluto wrote: post #27

Earlier quoted context omitted.

> But it's also an important reminder that our super accurate GPS measurements are not 100% reliable over time. The earth moves. This is IMO an odd statement. Land moves, and we can measure that movement extremely precisely. If software was more competent, we would record positions in four dimensions: space and time, relative to a well defined coordinate system. And we could map a position at one time to a position a…

It’s not just a software problem, you also need to know how the earth is being deformed which is far more difficult than you might think.

Not necessarily. Place a grid of receivers in fixed locations and observe their reported position. That grid is then the transform you need between the map when they were placed and the current state of the globe.

A question would be how many you need, but these movements are on a large scale and receivers are dirt cheap.

Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#36

Post by amluto »

chrismorgan wrote: post #34
amluto wrote: post #27

Earlier quoted context omitted.

> But it's also an important reminder that our super accurate GPS measurements are not 100% reliable over time. The earth moves. This is IMO an odd statement. Land moves, and we can measure that movement extremely precisely. If software was more competent, we would record positions in four dimensions: space and time, relative to a well defined coordinate system. And we could map a position at one time to a position a…

This is how things are done. You specify the datum, coordinates, and time. Geodetic datums are time-dependent transformation functions. Any software that is recording points at the particular time called “now” and not either recording the coordinates and time, or reprojecting them to a meaningful reference datum at its epoch (origin in time), is bad .

As far as I can tell, GIS software is bad, then. I spent longer than seemed at all reasonable trying to research this with QGIS, and I got nowhere. ArcGIS (which I don’t have) wasn’t obviously better.

Do you have an example of good software?

Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#37

Post by lawlessone »

rzzzt wrote: post #29
borgunit2 wrote: post #21

Earlier quoted context omitted.

That’s not kinetic earthquake energy, though. I think in an apples-to-apples comparison, you would need to attach some kind of device to absorb the kinetic energy from the fault.

A building-sized piezo crystal?

Country sized.

Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#38

Post by thehours »

IKantRead wrote: post #31
sandworm101 wrote: post #2

The amount of energy released in such events boggles the mind. Shifting cubic-kilometers of rock, in this case several hundred or even thousands of cubic-kilometers, even a few inches requires more energy than all the worlds nukes many times over. We live atop an immense heat engine, every little vibration of which could power our entire civilization for years.

I've always found it fascinating that geophysicist and earlier advocate for Bayesian methods, Sir Harold Jeffreys, didn't believe in continental drift and plate tectonics because he felt there was no known source of energy on the Earth massive enough to explain this movement. [0] He remained an opponent until death (at which point continental drift was widely accepted) which is both a testament to the literally unbel…

Actually the lesson I take away is the importance of not having a 0% (or 100%) prior, since it leaves no room to update with new information.

Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#39

Post by chrismorgan »

amluto wrote: post #36
chrismorgan wrote: post #34

Earlier quoted context omitted.

This is how things are done. You specify the datum, coordinates, and time. Geodetic datums are time-dependent transformation functions. Any software that is recording points at the particular time called “now” and not either recording the coordinates and time, or reprojecting them to a meaningful reference datum at its epoch (origin in time), is bad .

As far as I can tell, GIS software is bad , then. I spent longer than seemed at all reasonable trying to research this with QGIS, and I got nowhere. ArcGIS (which I don’t have) wasn’t obviously better. Do you have an example of good software?

Sorry, no. This was my dad’s field, not mine, so I’ve just got a bunch of second-hand info and know that the software he worked on (two pieces, one for a company and one of his own) handled these sorts of things correctly. And I find it genuinely impossible to imagine that major GIS software would not handle this, because it’s so fundamental.

Your GIS software will have you set a base CRS, and then, presuming it’s not recording time on points, all coordinates will be relative to it at its epoch. That’s all you need, now if you want to see what it’s like now, you project it accordingly. Anything along the lines of recording new points based on actual measurements should obviously either record time and position, or just position after performing the reverse transformation. But there you’d tend to be getting beyond the domain of what the bulky GIS software is doing, and into the domain of specific-purpose mobile apps and such.

Re: Earthquake in Japan yesterday may have shifted land 1.3 meters

#40

Post by bee_rider »

chrismorgan wrote: post #30
throw0101d wrote: post #3

Australia updated its latitude and longitude somewhat recently because of continental drift: > The Geocentric Datum of Australia, the country’s local coordinate system, was last updated in 1994, and Australia is now about 1.5m further north-north-east (or, to give the metric used in a BBC infographic: about the height of a kangaroo). * https://www.theguardian.com/science/2016/aug/03/mind-the-gap... * https://www.ga.g…

Australia’s geocentric datum is pretty boring, because Australia’s tectonics are pretty boring. We just don’t get large earthquakes. So the GDA94 → GDA2020 update is actually pretty minor. If my understanding is correct, the 1.8m difference sometimes talked of between ITRF92 and GDA94 by 2020 is actually irrelevant so long as you do proper projection of your coordinates, which you should , but some things don’t—and s…

Hi from New England, middle-of-the-plate buddy. In fact, it had never occurred to me that the mapping of parts of the ground to, like, latitude-longitude could be time dependent, haha. I guess this could make a big difference in surveying.
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