
Prompt elasto-gravity signals and their potential use in modern seismology - dnetesn
https://phys.org/news/2020-02-earthquakes-deform-gravity.html
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MeteorMarc
Why would LIGO
([https://www.ligo.caltech.edu/](https://www.ligo.caltech.edu/)) not detect
these signals?

~~~
mokus
Speculation here, but from the article’s description I suspect these are too
high in magnitude (they would likely saturate the sensors) and not the right
“mode” or frequency. The LIGO method is looking for very small fluctuations in
a more complex field (certain components of the “metric tensor” which amounts
to measuring tiny time-dependent variations in the speed of light in two
different directions). By contrast, this signal would be a change in the
direction and strength of gravity’s local pull and is probably one of the
things they work hard to filter out at LIGO. As such, the main instrument
probably wouldn’t be able to measure them accurately, but I’d expect the
instruments used to maintain and isolate the main instrument would see it
pretty well.

Similar in concept to how a radio antenna isn’t the best way to measure a
shift in the local magnetic field. It’s the “same” thing, but the instrument
is sensitive to a very different part of the space of “magnetic field
changes”, including in this case the fact that the antenna may actually be
measuring the field by looking at different data (electric field) and relying
on the way the two interact in the “far field”.

Edit: sorry for the abuse of scare quotes, I’m on mobile and it’s the easiest
way I can think of right now to indicate that I’m oversimplifying certain
technical digressions that are deep subjects in their own right

~~~
jcims
I did some stubby pencil work a while back and if I recall correctly, the mass
energy conversion of 1kg of material (i.e. nuclear test) on the other side of
the planet was orders of magnitude 'louder' than anything that LIGO has
detected so far.

It still suffers from having no chirp before that you get from two orbiting
bodies that merge, but I think it would technically be detectable as a pop in
the signal.

------
merricksb
Original paper here:

[https://www.sciencedirect.com/science/article/abs/pii/S00128...](https://www.sciencedirect.com/science/article/abs/pii/S0012821X20300935)

