>A single interrogator can cover some 40 kilometers of fiber, Biondi says, and monitor a virtual sensor every couple of meters.
Earthquake engineer here. This is the cool part. We've got plenty of data to detect and locate any given earthquake occurred. And we have maps that show approximately how hard the soil is under any given site. But the intensity that any building sees is still only known to +-50%, mostly due to variation in the subsurface conditions that we don't have enough resolution to model.
We're not currently able to predict the actual earthquakes at all, only probabilities of likelihood on very large timescales. I could see it being useful to predict future damages to certain buildings/areas based on existing data, assuming an earthquake happened.
I've heard that internal buses in high performance aircraft also use time-domain reflectometry such as this to detect wiring faults before they interrupt service.
> An “interrogator” installed at one end of the line sends pulses of laser light into the fiber and monitors the light that bounces back—the backscatter. Changes in the timing of backscattering occur when the fiber stretches and contracts—something that happens when the ground moves during an earthquake.
Ping-based earthquake detection? Could ping jitter of existing optical networks be used for this purpose?
I had never thought about thermal and mechanical expansion of fiber optics - it's in the same vein as LIGO/VIRGO - could we one day see a fiber optic network used for both data transmission and gravity wave detection?
(I once ran fiber about 200 feet through a welding shop, to connect an ancient PlasmaCAD to a null modem. But we couldn't get the fiber in a spool of less than 500 feet, so it was mostly a spool in the office.)
Ligo/Virgo uses a number of extraordinary means to cancel out things like earthquakes or rumblings, local vibrations and so on. But I wonder if you had 1000's of mile of fiber in disparate parts of the world if it would be possible to cancel out the noise and see gravitational waves? Probably not, shrug. But still I find it a fascinating thought. Also, cool idea to measure earthquakes.
The degree of engineering required to detect gravitational waves, level of precision, it’s both incredibly difficult technically, and very expensive. Unless you’re looking to detect gravitational waves we would have no reason to engage in that kind of expense and difficulty, so no fiber optics will never be that for us.
Detecting earthquakes accurately (mostly by subtracting noise) has historically been technically difficult, as well. I wonder how many orders of magnitude more noise reduction is required for gravitational waves, as compared to earthquakes.
It's hard to even imagine this kind of precision. I wonder what would happen if a gravitational wave would hit us that would cause displacement on the same order of magnitude an earthquake causes. Would this rip the planet apart or would just nothing happen?
To experience that, you’d need to be so close to some very extreme event (neutron star merger for example) that you’d already be in desperate trouble, and a planet wouldn’t hold together. You could hypothetically experience something less impressive than an earthquake, but less impressive than having your atoms strung out like spaghetti.
Fiber-Optic Intrusion Detection Systems (FOIDS) are often used in physical fenceline security [0], with permanent installations using hardened conduit or impromptu setups of kevlar-jacketed fiber, zip-ties and concertina wire. It's only natural that longer runs of fiber can be used for similar vibration measurements.
Earthquake engineer here. This is the cool part. We've got plenty of data to detect and locate any given earthquake occurred. And we have maps that show approximately how hard the soil is under any given site. But the intensity that any building sees is still only known to +-50%, mostly due to variation in the subsurface conditions that we don't have enough resolution to model.