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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

#11

Post by falcolas »

philip1209 wrote: post #5

How property rights work when land shifts?

As I understand it (at least in the US), your land rights are based off of relative measurements from a static (to the land) point. They often look like medallions on the ground, anchored in place by fairly sizable stakes to ensure they don't easily move.

The positions of those medallions... not as sure, but I imagine they are in turn positioned according to other static points.

If the land cracks, well, I have no idea. That would be a legal battle no doubt.

EDIT: These fixed points are called "common points" or "points of beginning (POB)", and there's usually one per neighborhood. There are also apparently buried iron rods (survey pins) that define property lines that can be found using a metal detector or such, but they are not foolproof.

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

#12

Post by taeric »

dboreham wrote: post #9
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…

Locations inside a country (e.g. plat map boundaries) don't use latitude/longitude.

They didn't used to. And, of course you are correct that survey markers are to landmarks. But, more and more people are using data from online mapping services, that largely think they can store locations in lat/lng. People seem to trust that as "the UTC of location data."

That said, those can be just as fraught, no? Since movement will not be fully uniform for the entire continent? And landmarks aren't static things, either? I'm curious how landmarks are done to preserve this, long term?

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

#13

Post by taeric »

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…

I'm also curious if anyone has a good article to read on how this is managed. My guess would be that you have reference points and sets of nearby things that are recorded relative to the closest reference point. As noted in the sibling, your plat map is likely set against a local landmark. (Though, even there, they often also include the lat/lng of where it is expected to be found.)

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

#14

Post by samstave »

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...

>reminder that our super accurate GPS measurements are not 100% reliable

Lockheed solved this with their super sensitive Magnetic Field 'GPS' device - which they claim if for having 'GPS' accuracy for aircraft and ships nearly 100% based on the localized magnetic signature of the earth - but we all know these are actually built for subterranian/submarine environs where space based GPS no cut it. Can't navigate Agartha without it.

https://www.gpsworld.com/quantum-magnetometer-senses-its-pla...

I do wonder how much major earthquakes affect the finer signature of the magnetic fields?

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

#15

Post by badcppdev »

dataflow wrote: post #7
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...

I'm confused, how does moving 2.7 inches a year translate into 656 feet over 25 years? Was it moving tens or hundreds of times faster a few decades ago?

I assume that should be 6.56 feet or some similar miscalculation converting from metric to imperial measurements

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

#16

Post by eesmith »

dboreham wrote: post #9
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…

Locations inside a country (e.g. plat map boundaries) don't use latitude/longitude.

Some places use an encoded lat/long.

Open Location Code - "Google has shown practical usage of plus codes for addressing purposes in Cape Verde,[10] parts of Kolkata[11] and Kolhapur[12] in India, and the Navajo Nation in the United States.[13]" - https://en.wikipedia.org/wiki/Geocode . https://freethoughtblogs.com/singham/2023/12/24/using-olc-co... says a friend of his sent an OLC coordinate to get to a place in Carmel-by-the-Sea, California, which (infamously?) has no street numbers.

What3words - "This population had "no consistent addressing system" until May 2016 when Mongol Post started using a geocoding system provided by what3words." - https://en.wikipedia.org/wiki/Mongol_Post

Over time (centuries?) the named coordinate will no longer be valid as the location is no longer near enough to that lat/long.

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

#17

Post by burkaman »

dataflow wrote: post #7
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...

I'm confused, how does moving 2.7 inches a year translate into 656 feet over 25 years? Was it moving tens or hundreds of times faster a few decades ago?

Basically, before 1994 the official Australia coordinate system was not optimized for GPS, which was not common when the system was developed, and so didn't exactly align with global coordinates. The 656 foot change was mostly about that, not about tectonic changes.

AGD is Australian Geodetic Datum of 1984 and GDA94 is Geocentric Datum Of Australia 1994.

> The AGD provided a reference system that best fit the shape of the earth in the Australian Region but its origin did not coincide with the centre of mass of the earth. National datums were commonly non-geocentric before satellite based navigation systems were established in the early 1970’s. The distance between the origin points of GDA94 and AGD is approximately 200 metres. When the coordinates of a point on the Earth’s surface are converted from AGD to GDA94 this translates to a coordinate difference of approximately the same amount. The difference varies slightly depending on where you are in Australia.

- https://www.icsm.gov.au/datum/australian-geodetic-datum-1966...

> Previously, a change of about 200 metres occurred in the year 2000 when Australia shifted from the Australian Geodetic Datum 1984 (AGD84) to the Australian Geocentric Datum 1994 (GDA94).

- https://www.dmp.wa.gov.au/News/Geocentric-Datum-of-Australia...

Nowadays you can use the Australian Terrestrial Reference Frame, which is time dependent and automatically adjusts to compensate for tectonic movement: https://www.icsm.gov.au/australian-terrestrial-reference-fra....

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

#18

Post by rwmj »

philip1209 wrote: post #5

How property rights work when land shifts?

In Japan property boundaries are (often) marked with physical markers embedded into the ground: https://www.japantimes.co.jp/community/2015/01/02/how-tos/pr... https://japanpropertycentral.com/real-estate-faq/land-bounda...

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

#19

Post by throw0101d »

badcppdev wrote: post #15
dataflow wrote: post #7

Earlier quoted context omitted.

I'm confused, how does moving 2.7 inches a year translate into 656 feet over 25 years? Was it moving tens or hundreds of times faster a few decades ago?

I assume that should be 6.56 feet or some similar miscalculation converting from metric to imperial measurements

> 6.56 feet

Statute feet or survey feet?

* https://www.nist.gov/pml/us-surveyfoot

* https://oceanservice.noaa.gov/geodesy/international-foot.htm...

* https://en.wikipedia.org/wiki/Foot_(unit)#U.S._survey_foot

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

#20

Post by Symbiote »

falcolas wrote: post #11
philip1209 wrote: post #5

How property rights work when land shifts?

As I understand it (at least in the US), your land rights are based off of relative measurements from a static (to the land) point. They often look like medallions on the ground, anchored in place by fairly sizable stakes to ensure they don't easily move. The positions of those medallions... not as sure, but I imagine they are in turn positioned according to other static points. If the land cracks, well, I have no id…

The more common points are called trigonometrical points or triangulation stations.

https://en.wikipedia.org/wiki/Triangulation_station

https://en.wikipedia.org/wiki/Point_of_beginning

(I'm surprised there's no link between these two articles.)

https://en.wikipedia.org/wiki/Initial_point

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