Gravity Signals Could Detect Earthquakes At the Speed of Light (science.org) 21
sciencehabit shares a report from Science.org: Two minutes after the world's biggest tectonic plate shuddered off the coast of Japan, the country's meteorological agency issued its final warning to about 50 million residents: A magnitude 8.1 earthquake had generated a tsunami that was headed for shore. But it wasn't until hours after the waves arrived that experts gauged the true size of the 11 March 2011 Tohoku quake. Ultimately, it rang in at a magnitude 9 -- releasing more than 22 times the energy experts predicted and leaving at least 18,000 dead, some in areas that never received the alert. Now, scientists have found a way to get more accurate size estimates faster, by using computer algorithms to identify the wake from gravitational waves that shoot from the fault at the speed of light.
Recently, researchers involved in the hunt for gravitational waves -- ripples in space-time created by the movement of massive objects -- realized that those gravity signals, traveling at the speed of light, might also be used to monitor earthquakes. "The idea is that as soon as mass moves anywhere, the gravitational field changes, and ... everything feels it," says Bernard Whiting, a physicist at the University of Florida who worked on the Laser Interferometer Gravitational-Wave Observatory. "What was amazing was that the signal would be present even in seismometers." Sure enough, in 2016, Whiting and his colleagues reported that regular seismometers could detect these gravity signals. Earthquakes result in large shifts in mass; those shifts give off gravitational effects that deform both existing gravitational fields and the ground beneath seismometers. By measuring the difference between these two, the scientists concluded they could create a new kind of earthquake early warning system. Gravitational signals show up on seismometers before the arrival of the first seismic waves, in a portion of the seismogram that's traditionally ignored. By combining signals from dozens of seismometers on top of one another, scientists can identify patterns to interpret the size and location of large events, Whiting says.
Now, Andrea Licciardi, a postdoc at Cote d'Azur University, and his colleagues have built a machine-learning algorithm to do that pattern recognition. They trained the model on hundreds of thousands of simulated earthquakes before testing it on the real data set from Tohoku. The model accurately predicted the earthquake's magnitude in about 50 seconds -- faster than other state-of-the-art early warning systems, researchers report today in Nature. "It's more than the seed of an idea -- they've shown that it can be done," Whiting says. "What we showed was a proof of principle. What they're showing is a proof of implementation."
Recently, researchers involved in the hunt for gravitational waves -- ripples in space-time created by the movement of massive objects -- realized that those gravity signals, traveling at the speed of light, might also be used to monitor earthquakes. "The idea is that as soon as mass moves anywhere, the gravitational field changes, and ... everything feels it," says Bernard Whiting, a physicist at the University of Florida who worked on the Laser Interferometer Gravitational-Wave Observatory. "What was amazing was that the signal would be present even in seismometers." Sure enough, in 2016, Whiting and his colleagues reported that regular seismometers could detect these gravity signals. Earthquakes result in large shifts in mass; those shifts give off gravitational effects that deform both existing gravitational fields and the ground beneath seismometers. By measuring the difference between these two, the scientists concluded they could create a new kind of earthquake early warning system. Gravitational signals show up on seismometers before the arrival of the first seismic waves, in a portion of the seismogram that's traditionally ignored. By combining signals from dozens of seismometers on top of one another, scientists can identify patterns to interpret the size and location of large events, Whiting says.
Now, Andrea Licciardi, a postdoc at Cote d'Azur University, and his colleagues have built a machine-learning algorithm to do that pattern recognition. They trained the model on hundreds of thousands of simulated earthquakes before testing it on the real data set from Tohoku. The model accurately predicted the earthquake's magnitude in about 50 seconds -- faster than other state-of-the-art early warning systems, researchers report today in Nature. "It's more than the seed of an idea -- they've shown that it can be done," Whiting says. "What we showed was a proof of principle. What they're showing is a proof of implementation."
Near field I assume (Score:4, Interesting)
The idea is fine, I'm just being (overly) picky about the terminology and want to distinguish these gradient changes from propagating waves.
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The idea is fine, I'm just being (overly) picky about the terminology and want to distinguish these gradient changes from propagating waves.
Nothing is more annoying than getting an axiom backwards, imagine gradient instead defined by mass holes.
Terminology failure (Score:4, Interesting)
Nope. It's a common mistake since the terminology is confusing.
Gravitational waves are waves cause by gravitational distortions, which change the shape of spacetime and propagate at light speed. Which is what you (and the article) are describing.
Gravity waves are vertical-displacement waves such as those in the ocean (and atmosphere), whose propagation depends on gravity supplying a "return to neutral" force.
The name "gravity waves" had already been in common use long before the possibility of gravitational waves had been proposed, so they get first dibs on the name - to the confusion and frustration of many.
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Just to clarify since I phrased that first description poorly:
"Gravitaional distortions" = masses moving relative to each other, changing the shape of the gravitational field.
A better phrasing would have been
Gravitational waves are waves caused by masses moving relative to each other, which changes the shape of spacetime and propagates at light speed. Which is what you (and the article) are describing.
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This works the way they want . The nitpicking part is that its not really gravitational radiation, but a near f
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They specifically say they travel at light speed - I don't think mechanical waves can do that.
The signal would be fantastically small - but also fantastically close so it wouldn't decay much. As I recall, most of the black hole mergers we've detected are believed to be from other galaxies - so at least millions of light years distant, for an attenuation by a factor of at least 10^30 compared to a shifting mass on the other side of Earth. (and probably much larger since they're mostly from distant galaxies -
Gravity waves (Score:3)
A few years ago, I borrowed a book about wave motion from a friend of mine. I have done some work on mechanical waves, related to bulk sound transmission in gases, liquids, and solids. Surface waves in liquids are an utterly different phenomenon. In the book, these are called "gravity waves", which is maybe a bit confusing. The interesting stuff is when you consider the propagation of a hump of liquid, with the competing forces of the mass of the liquid, and the force of gravity. This has some resemblance to wave motion in a guitar string, which has a certain mass per unit length, and a tension. It is not that difficult to work out the resonant frequencies.
Surface waves in liquids, so called gravity waves, are totally weird shit in comparison to my musical acoustics. The speed of a gravity wave depends in its wavelength. The longer the wavelength, the faster the wave. This means that an earthquake under the deep ocean can launch a wave travelling at hundreds of miles an hour. Another point with gravity waves is that the velocity of the wave is dependent on the depth of water under the wave. The shallower the water, the slower the wave, This means that a hump of water created in the deep ocean, travelling at hundreds of miles an hour, piles up into a huge wave when it reaches land, because the slowed down wave in shallow water is being fed by the faster deep ocean wave. As far as I know, this is the primary mechanism behind tsunamis.
Another observation about gravity waves is the wake created by a surface vessel, or a swimming water bird. In acoustics, there is a speed of sound, and an object travelling faster than this speed creates a conical wake, which causes a sonic boom. With surface waves in liquids, all objects create a wake, no matter how fast they are travelling. Having learned this, I observed the behaviour of canal boats and ducks, at a pub in the country next to a canal. Sure enough, the angle of the wake was the same for boats and ducks. Some patience is required in order to observe a duck travelling at constant velocity, but after sufficient imbibing of fermented apples, I was rewarded with a perfect demonstration of the mathematical principles.
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A few years ago, I borrowed a book about wave motion from a friend of mine. I have done some work on mechanical waves, related to bulk sound transmission in gases, liquids, and solids. Surface waves in liquids are an utterly different phenomenon. In the book, these are called "gravity waves", which is maybe a bit confusing.
Yep that is pretty confusing for most people which is why I usually refer to them as 'ocean waves' (even though they can obviously propagate in any body/amount of any liquid) so as to not confuse them with gravitational waves (i.e. the waves from black holes detected by LIGO et al.). You're right that ocean waves are particularly weird, basically it's because they exist at the boundary between two mediums, rather than propagating within a given medium. Another way they are really weird is they cannot be e
Gravity propogation (Score:3)
That answers a physics question I've had for a long time, how fast does gravity "travel?" Apparently it's at the speed of light.
Re:Gravity propogation (Score:5, Informative)
That answers a physics question I've had for a long time, how fast does gravity "travel?" Apparently it's at the speed of light.
We didn’t actually measure this until in 2017 LIGO measured an event we could also detect light from. Now we know it’s the same to at least 15 decimal places or so. We had just assumed it was true from relativity.
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Interesting, thanks for letting me know.
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So here's a dumb question for you (note: I'm not a scientist...)
If gravity travels at the speed of light, then why don't we when we fall, seeing as how we are constrained by gravity?
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It takes time to accelerate you to that speed. (Also, relativity comes into effect, so unless your mass is as small as a packet of photons, you will never quite reach the speed of light).
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That answers a physics question I've had for a long time, how fast does gravity "travel?"
Just type it into google...
(Or ask Siri, I'm sure she knows)
The alert could arrive yesterday. (Score:2)
Another Italian invention that Italians won't get (Score:2)
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That the names look Italian and French is not surprising, the university Côte d'Azur is just 40 km from the international border.
Detecting moving objects by gravity? (Score:1)
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As the technology gets better, its e