Earth’s mysterious hum recorded underwater for first time 

Posted: February 14, 2018 by oldbrew in physics, research
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Image credit: strangesounds.org


But amplitude variations in the hum did not correlate with the seasons as once thought.

Scientists finally capture hum coming from the centre of the Earth, reports GeologyIn.

Although we like to think we know everything – and technology has advanced so much we practically have the answer to everything we don’t know at our fingertips – there are still plenty of mysteries left to solve.

For the past few decades, something has been becoming increasingly clear: Earth constantly hums, even though we can’t hear it.

The first attempt to detect this hum was made in 1959, but it wasn’t until 1998 that a paper was finally published proving it.

Earth expands and contracts constantly, ever so slightly. This is known as “free oscillations”, and they register as a background vibrational signal – or hum – in the absence of any other seismic activity.

Now, for the first time, scientists have been able to record our planet’s hum from the bottom of the ocean.

There have been many observations made of Earth’s hum since that study in 1998. They confirm that the signal is real – but they’ve all been taken using seismometers on land.

Taking measurements on the bottom of the ocean is an important piece of the puzzle, not least because 70 percent of our planets surface is covered by water.

And having measurements from deep under the sea could help us figure out what’s really causing the hum.

A longstanding hypothesis is that Earth’s free oscillations are caused by the constant pounding of waves on the ocean floor, and there have been a number of studies demonstrating just how this could be the case.

Another version is that the hum is partially affected by atmospheric turbulence, since it is stronger in the northern hemisphere’s Pacific Ocean during the northern winter, and southern oceans during southern hemisphere winter, associated with winter storms.

In recent years, seismometer stations have been installed on the seafloor around the world, designed to capture seismic and acoustic signals.

But seismometers measure movement, and there’s a lot of that under the sea. Meanwhile, the signal of Earth’s permanent vibrations is very low frequency and very slight.

To find the signal of the hum, the researchers, led by Martha Deen at the Paris Institute of Earth Physics, first gathered 11 months worth of observation data from 57 seismometer stations on the seafloor in the Indian Ocean east of Madagascar, installed in 2012-2013 to study volcanic events.

They then selected the two stations that had the highest data quality, and painstakingly removed any sources of interference from identified sources.

After removing the signals caused by ocean infragravity waves, seafloor currents and electronic glitches, the noise level was equivalent to that of a terrestrial station.

In other words, what they had left was Earth’s hum. They then cross-referenced the signal they had with observations of the hum from terrestrial stations. They had a match.

Continued here.

Comments
  1. oldbrew says:

    Earth’s Inner Core Shouldn’t Technically Exist
    February 9, 2018

    The paradox at the center of our planet

    “Everyone, ourselves included, seemed to be missing this big problem,” study author Steven Hauck, a professor of Earth, Environmental and Planetary Sciences at Case Western Reserve University in Ohio, said in a statement. Namely, they were missing “that metals don’t start crystallizing instantly unless something is there that lowers the energy barrier a lot.”
    . . .
    “At the pressures of the core, it would have to cool 1,000 degrees Kelvin [726 degrees C or 1,340 degrees F] or more below the melting temperature in order to crystallize spontaneously from pure liquid,” Hauck told Live Science. “And that’s a lot of cooling, especially since at the moment, the scientific community thinks the Earth cools maybe about 100 degrees K per billion years.”

    http://www.livescience.com/61715-earth-inner-core-paradox.html

  2. The Bristol Hum is still baffling folks in the area, most annoying

  3. Jim says:

    Interestingly, even lava shows a scum. You know, that other chemicals that were mixed in the compound , that were not boiled away. That scum would act as an insulator around the ball of boiling rock. Slowing the cooling effect of space. And, how are they able to judge the tempreture of the ball, of the past, and date it? It’s just a waguess.

  4. A C Osborn says:

    I am not sure why they would be looking at seasons, I would have thought Planet Orbitals would be more likely, they are continually working on the Earth.

  5. Philip Foster (Revd) says:

    It seems that most stars, including our sun, also hum, a fact that has proved useful in analysing the ‘construction’ of the sun down to its core.
    I am put in mind of the words from the book of Job 38:7
    “…When the morning stars sang together,
    And all the sons of God shouted for joy…”

  6. oldbrew says:

    Not forgetting the Schumann resonances…

    The Schumann resonances (SR) are a set of spectrum peaks in the extremely low frequency (ELF) portion of the Earth’s electromagnetic field spectrum. Schumann resonances are global electromagnetic resonances, generated and excited by lightning discharges in the cavity formed by the Earth’s surface and the ionosphere.

    http://en.wikipedia.org/wiki/Schumann_resonances

  7. oldbrew says:

    Re seasonal theory:

    For reasons astronomers and geophysicists still don’t really understand, statistically more auroras are visible in September and March, which are the months near the spring and autumn equinoxes.

    http://otagomuseum.nz/blog/auroras-and-the-equinox/

    Looks like the hum is unrelated to auroras.

  8. Tim. says:

    Remnant vibration after the last big asteroid hit Earth? What is the Earth’s natural frequency?

  9. stpaulchuck says:

    Tim, interesting idea!

    for me I vote that it’s just an artifact of the Earth’s dynamo. It could either be a primary rotational frequency or a beat note. I’ve seen papers that believe there are a series of tubular rotating masses surrounding the central core.

    anyway, ain’t it fun? there is always something new to learn… if you look

  10. p.g.sharrow says:

    ain’t it fun? there is always something new to learn… if you look”

    Every day is an Easter Egg Hunt! on the World Wide Web…pg

  11. Doonhamer says:

    Frequency?
    And can whales “hear” it?

  12. oldbrew says:

    Scientists eavesdrop on volcanic rumblings to forecast eruptions
    February 16, 2018

    http://phys.org/news/2018-02-scientists-eavesdrop-volcanic-rumblings-eruptions.html

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