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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

#71

Post by cozzyd »

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…

I've always found it fascinating that the guy who came up with the theory (Wegener) died in on the ice sheet in Greenland while attempting to resupply a research station. Having spent some time on the Greenland Ice Sheet at Summit Station, life on the Greenland ice sheet is much more cushy nowadays...

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

#72

Post by helen___keller »

oasisbob wrote: post #50
robocat wrote: post #46

Earlier quoted context omitted.

> our super accurate GPS measurements are not 100% reliable over time The GPS measurements are 100% reliable. Think of it like getting GPS co-ordinates while on a boat - it's the boat that moves. A point of interest on land doesn't stay at the same latitude/longitude/altitude because land is a tectonic plate "boat" floating on the mantle. Close to the earthquake faultplane, land crumples and shears sideways and up/do…

> The GPS measurements are 100% reliable. Think of it like getting GPS co-ordinates while on a boat - it's the boat that moves. I'm not sure this is a good metaphor. When doing high-accuracy GNSS (GPS) survey work, a static reference station is typically used to help correct errors from the GPS measurements themselves. If GPS was 100% consistent and reliable, differential correction wouldn't be a common and often-req…

While you’re correct that GNSS is not 100% accurate (like everything in the physical world, it comes with error bars), I think the point stands that the error is unrelated to the movement of continents.

Ultimately GNSS is just measuring your position relative to some celestial objects using the time it takes for signals to propagate space (and some other info: their ephemerides, and a shared-ish clock). The fact that land exists, and where it exists, are not relevant

Your error corrections might be thrown off when the base station moves, but that’s not an issue of GNSS that’s an issue of RTK

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

#73

Post by midasuni »

gwright wrote: post #69
taeric wrote: post #13

Earlier quoted context omitted.

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.)

This is a good example of why capturing coordinates in a local spatial reference system may be better than capturing coordinates in a global spatial reference system. Global coordinates of a place of interest will drift relative to a global coordinate system but remain stable relative to a local coordinate system. This article illustrates that "stable" is not the same thing as unchanging in the presence of 7.5 earthq…

It’s similar to capturing future dates in local time including timezone. There’s no guarantee that 1300 london time on 20-Dec-2029 will be 1300UatC, as the U.K. may shift its daylight rules before then.

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

#74

Post by midasuni »

johncalvinyoung wrote: post #62
blacksmith_tb wrote: post #51

Earlier quoted context omitted.

For most surveying wouldn't the the relative, nearby points be shifting together equally?

not in California, Iceland, or Japan!

It’s unlikely the relative position of Griffiths Observatory and the Chinese Theatre would change though, both may shift north by 74cm relative to Las Vegas sure, but I’m not aware of any faults between those two points

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

#75

Post by midasuni »

eesmith wrote: post #16
dboreham wrote: post #9

Earlier quoted context omitted.

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 Car…

I believe W3W are 1m squares, so in Japan it sounds like they may be already broken

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

#76

Post by dnedic »

helen___keller wrote: post #72
oasisbob wrote: post #50

Earlier quoted context omitted.

> The GPS measurements are 100% reliable. Think of it like getting GPS co-ordinates while on a boat - it's the boat that moves. I'm not sure this is a good metaphor. When doing high-accuracy GNSS (GPS) survey work, a static reference station is typically used to help correct errors from the GPS measurements themselves. If GPS was 100% consistent and reliable, differential correction wouldn't be a common and often-req…

While you’re correct that GNSS is not 100% accurate (like everything in the physical world, it comes with error bars), I think the point stands that the error is unrelated to the movement of continents. Ultimately GNSS is just measuring your position relative to some celestial objects using the time it takes for signals to propagate space (and some other info: their ephemerides, and a shared-ish clock). The fact that…

GNSS satellites talk to base stations on earth to get correction data using the measurements they obtain (including measurements obtained by tracking satellites from the ground). I believe this is what the poster above is reffering to.

RTK is a whole another beast and the meaning of an RTK base station is something else.

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

#77

Post by sangnoir »

midasuni wrote: post #73
gwright wrote: post #69

Earlier quoted context omitted.

This is a good example of why capturing coordinates in a local spatial reference system may be better than capturing coordinates in a global spatial reference system. Global coordinates of a place of interest will drift relative to a global coordinate system but remain stable relative to a local coordinate system. This article illustrates that "stable" is not the same thing as unchanging in the presence of 7.5 earthq…

It’s similar to capturing future dates in local time including timezone. There’s no guarantee that 1300 london time on 20-Dec-2029 will be 1300UatC, as the U.K. may shift its daylight rules before then.

That depends entirely ok whether the event being reflected is local or global. If its the time of an solar eclipse, for example, then its unaffected by daylight rules - unlike business hours and such. Working with dates/timestamps is a nightmare, but appears simple at first blush.

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

#78

Post by hackerlight »

blackbear_ wrote: post #70
throwup238 wrote: post #54

Earlier quoted context omitted.

Another great illustration of Planck’s law: > Max Planck, surveying his own career in his Scientific Autobiography, sadly remarked that “a new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.“ -The Structure of Scientific Revolutions

This is actually such a great insight. That's why we also need new generations of politicians and management every so often to keep the wheel of progress rolling. And, incidentally, why I think that developing anti-aging technology is not a good idea.

I wonder if there's something physical to do with aging that makes people cognitively inflexible. Anti-aging tech would be great if you could prevent that negative aspect of aging too.

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

#80

Post by eesmith »

midasuni wrote: post #75
eesmith wrote: post #16

Earlier quoted context omitted.

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 Car…

I believe W3W are 1m squares, so in Japan it sounds like they may be already broken

https://en.wikipedia.org/wiki/What3words says "What3words divides the world into a grid of 57 trillion 3-by-3-metre (10 ft × 10 ft) squares".

Australia moves about 7cm/year so after about 43 years a W3W coordinate no longer matches local coordinates.

It feels weird that a continent could move so much in someone's lifetime.

Looks like the 1906 San Francisco quake had displacements up to 8.5 meters, so more than two squares. https://en.wikipedia.org/wiki/1906_San_Francisco_earthquake

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