Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Earthquake in Japan yesterday may have shifted land 1.3 meters

www3.nhk.or.jp

Post reply on HN
Print view View original

61–70 of 87 posts

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

#61

Post by pxeboot »

bobthepanda wrote: post #49
KeplerBoy wrote: post #45

Earlier quoted context omitted.

GPS is much better than 16 feet these days. Nobody asks google maps for instructions how to move 10 miles southwest. We ask it to provide a route to a specific latitude and longitude, that's global navigation and that, of course, doesn't work if the place you want to get to has gotten new coordinates overnight.

That 16 ft figure is provided by the government. https://www.gps.gov/systems/gps/performance/accuracy/ And of course, satellite navigation is worsened by the urban canyon of buildings, terrain, trees etc so super accurate navigation also uses local cell towers, which are also shifting by the same magnitude and direction as you and your local destination. Ultimately people only really need to get to the rough city blo…

From that source:

> GPS-enabled smartphones are typically accurate to within a 4.9 m (16 ft.) radius

Smartphones were typically optimized for speed and battery life, not accuracy. Now that Multi-Band GPS is available on high end smartphones, they tend to be more accurate.

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

#62

Post by johncalvinyoung »

blacksmith_tb wrote: post #51
bee_rider wrote: post #40

Earlier quoted context omitted.

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.

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

not in California, Iceland, or Japan!

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

#63

Post by WJW »

pxeboot wrote: post #61
bobthepanda wrote: post #49

Earlier quoted context omitted.

That 16 ft figure is provided by the government. https://www.gps.gov/systems/gps/performance/accuracy/ And of course, satellite navigation is worsened by the urban canyon of buildings, terrain, trees etc so super accurate navigation also uses local cell towers, which are also shifting by the same magnitude and direction as you and your local destination. Ultimately people only really need to get to the rough city blo…

From that source: > GPS-enabled smartphones are typically accurate to within a 4.9 m (16 ft.) radius Smartphones were typically optimized for speed and battery life, not accuracy. Now that Multi-Band GPS is available on high end smartphones, they tend to be more accurate.

Also almost every smartphone I know of has acceleration sensors and can do Kalman filtering of the GPS position to achieve a much higher accuracy in practical use, even if the individual measurements are only accurate to ~5 meters.

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

#64

Post by samstave »

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…

Could even use this as a revers GLOBAL ORBITING SYSTEM [GoS] - Whereby a single satellite|probe dispels a lander to a planet with the Quantum Magnetic Cannister, and that QMC signals its global location to the satellite launcher, and the satellit can extrap its location based on the absolute location of the ground guys... (might need more than one ground magnet-moles?)

How can this be measured? Can fluidx3d do martian magnetics? [0]

--

[0] https://github.com/ProjectPhysX/FluidX3D

---

EDIT: "Mars does not have a magnetosphere"

ELI5: "how do electronics work when there is zero magnetic field around them? A complete antimagnetic environ?"

I've never heard any mention about making any electrical device work on a planet (such as mars) in a complete magnetically dark location?

How is there gravity on mars if there is no magnetic field for a planet, and how can mass, the size of a planet not produce magnetism/gravity if its not made of iron-sh (the RED of the planet)

ELI5, please.

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

#65

Post by kulahan »

barbariangrunge wrote: post #43
cm2187 wrote: post #6

Earlier quoted context omitted.

It's even harder than harvesting lightnings.

A friend, back when he was a physics student, looked into harvesting lightning. He calculated that it wasn't economically viable: tons of wattage, but for such brief timespans, that it doesn't actually amount to that much on a comparative scale. The cost of building the collectors and transporting the electricity (from ocean platforms) was much higher than the cost of using other energy sources. Iirc. It wasn't exact…

I know embarrassingly little about electricity, but wouldn't this also likely require significant advances in semiconductors to even be feasible?

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

#66

Post by samstave »

pxeboot wrote: post #61
bobthepanda wrote: post #49

Earlier quoted context omitted.

That 16 ft figure is provided by the government. https://www.gps.gov/systems/gps/performance/accuracy/ And of course, satellite navigation is worsened by the urban canyon of buildings, terrain, trees etc so super accurate navigation also uses local cell towers, which are also shifting by the same magnitude and direction as you and your local destination. Ultimately people only really need to get to the rough city blo…

From that source: > GPS-enabled smartphones are typically accurate to within a 4.9 m (16 ft.) radius Smartphones were typically optimized for speed and battery life, not accuracy. Now that Multi-Band GPS is available on high end smartphones, they tend to be more accurate.

They add fuzz to RSSI algos due to accelerometers trying to predict direction ofmotion for telemetry aiming.

swarm that on that backend with GPS tlemetry and typical rssi from cell towers, and the IMEI - and you have precise targets... with bios on the tracker (phone) - cams, gait, finger, face, voice, face... May as well start developing smart fabric... Oh wait...

:-)

Cyberpunk is dystopian by mr(crisper)DNA (TM)

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

#67

Post by shagie »

Out There Learning - The Greatest Ever On-Land Fault Movement - https://youtu.be/LUsIIJwxPYU (length: 4m 25s)

> Where is the world's greatest known on-land fault movement of any individual earthquake? It's at a place called Pigeon Bush near Wellington New Zealand. It is the surface trace of the Wairarapa Fault. In 1855 a magnitude 8.2 earthquake offset a small stream bed by about 18.5 metres which is the greatest single-event fault movement of any on-land fault in the globe!

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

#68

Post by tmm »

taeric wrote: post #12
dboreham wrote: post #9

Earlier quoted context omitted.

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…

> And landmarks aren't static things, either? I'm curious how landmarks are done to preserve this, long term?

At least in the US, the people in charge of this (the National Geodetic Survey) take movement into account. This[1] is the datasheet for the reference monument nearest my house. It has data for 3D velocity of the reference point.

    VX =  -0.0150 m/yr      northward =   0.0040 m/yr
    VY =  -0.0008 m/yr      eastward  =  -0.0148 m/yr
    VZ =   0.0030 m/yr      upward    =  -0.0002 m/yr
I'm not sure what the difference is between VX/VY/VZ and northward/eastward/upward, but those numbers are bigger than I thought they'd be. 15 mm/yr seems like a lot!

The official coordinates get updated from time to time, and in-between, perhaps you're supposed to adjust your measurements using that movement data (IANAS)? If there is a significant measured change in location due to an earthquake, I'm sure that data would be included in the monument datasheet or a new set of coordinates would be published.

FWIW, I went looking to see when the last earthquake was here in Maryland and it turns out there was one today[2].

[1] https://www.ngs.noaa.gov/cgi-cors/CorsSidebarSelect.prl?site... [2] https://www.abc27.com/news/top-stories/2-3-magnitude-earthqu...

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

#69

Post by gwright »

taeric wrote: post #13
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.)

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 earthquakes.

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

#70

Post by blackbear_ »

throwup238 wrote: post #54
IKantRead wrote: post #31

Earlier quoted context omitted.

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…

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.
Post reply on HN