To those skeptical of the calculations and if this is measureable:
1. I bet the modelling took construction sites data, which has been accumulated a long ago. You probably didn't know, but constructors know that big buildings tend to sink by several centimeters during and a bit after construction, and there are data and simple calculation models for that. At least this is what my friends in construction engineering say.
(When I started reading, I expected this to be based on Earth crust models -- there are cases with Scandinavia that rises 1 cm per year because 10K years ago the big think glaciers melted, and pressure on crust lowered a lot -- but seems it's not the case.)
2. Many cities have land fixtures for land lots marking, and geodesic work at construction sites. You must have such fixtures, rough or fine, or you'll end up learning that your wall is projected into the adjacent building by several cm/inches, and you need to adjust the project, or, opposite, with a big gap between them.
So there's geodesic fixtures everywhere in the cities. In Germany, you can see them on kerb stones, like a big jeans button, 3-5 cm (2") wide, with a small hole in the middle as an aim. In other cities they're less pronounced, but they do exist.
3. Geodesists routinely measure the drift of such fixtures, because the ground drifts both with Earth crust alltogether, and locally, and you must know where and how much.
I'm sure such small drift relative to other shores this is measureable over decades. Not sure one can deduct it over a couple of years though, as it's just too much distance vs little drift.
But you can probably measure the drift of a grid of fixtures inside Manhattan itself and notice the trends.
Satellite measurements are not that reliable as many think, as GPS signal has interferences and error margin of a meter, and I speculate thatlocal GPS stations get their coordinates by manual input based on local geodesic fixtures.
1. I bet the modelling took construction sites data, which has been accumulated a long ago. You probably didn't know, but constructors know that big buildings tend to sink by several centimeters during and a bit after construction, and there are data and simple calculation models for that. At least this is what my friends in construction engineering say.
(When I started reading, I expected this to be based on Earth crust models -- there are cases with Scandinavia that rises 1 cm per year because 10K years ago the big think glaciers melted, and pressure on crust lowered a lot -- but seems it's not the case.)
2. Many cities have land fixtures for land lots marking, and geodesic work at construction sites. You must have such fixtures, rough or fine, or you'll end up learning that your wall is projected into the adjacent building by several cm/inches, and you need to adjust the project, or, opposite, with a big gap between them.
So there's geodesic fixtures everywhere in the cities. In Germany, you can see them on kerb stones, like a big jeans button, 3-5 cm (2") wide, with a small hole in the middle as an aim. In other cities they're less pronounced, but they do exist.
3. Geodesists routinely measure the drift of such fixtures, because the ground drifts both with Earth crust alltogether, and locally, and you must know where and how much.
I'm sure such small drift relative to other shores this is measureable over decades. Not sure one can deduct it over a couple of years though, as it's just too much distance vs little drift.
But you can probably measure the drift of a grid of fixtures inside Manhattan itself and notice the trends.
Satellite measurements are not that reliable as many think, as GPS signal has interferences and error margin of a meter, and I speculate thatlocal GPS stations get their coordinates by manual input based on local geodesic fixtures.