The Northeast Greenland Ice Stream provides about 12% of the island's annual ice discharge, and so far, models cannot accurately capture just how quickly the ice moves. Researchers deployed a fiber-optic cable into a borehole and set explosive charges on the ice to capture images of its interior through seismology. But in the process, they measured seismic events that didn't correspond to the team's charges. (Image credit: L. Warzecha/LWimages; research credit: A. Fichtner et al.; via Eos)
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After my eyes became accustomed to the darkness I noticed that the spot seemed quite unsteady. Clearly this was more that what could be due to the continuous trembling of the earth, to the 'microseisms' that are caused by the pounding of the ocean waves on the shores of the Continent. It was due to the movements of my own eyes which in the darkness were not steadied by the surrounding picture of solid objects. Soon the luminous point gave me the feeling of being aboard a gently and irregularly moving vessel, so I braced a pencil on a piece of the apparatus and held it close to the luminous point. Now the point seemed steady and I felt as if I had come back to solid ground again. This was about the time of the actual shot. Nothing happened or could have happened. About a quarter of an hour was required for the shock to travel, deep under the Pacific basin, to the Californian coast. I waited with little patience, the seismograph making at each minute a clearly visible vibration which served as a time signal. At last the time signal came that had to be followed by the shock from the explosion and there it seemed to be: the luminous point appeared to dance wildly and irregularly. Was it only that the pencil which I held as a marker trembled in my hand? I waited for many more minutes to be sure that the record did not miss any of the shocks that might follow the first. Then finally the film was taken off and developed. By that time I had almost convinced myself that I must have been mistaken and that what I saw was the motion of my own hand rather than the signal from the first hydrogen bomb. Then the trace appeared on the photographic plate. It was clear and big and unmistakable. It had been made by the wave of compression that had traveled for thousands of miles and brought the positive assurance that Mike was a success.
"Brighter than a Thousand Suns: A Personal History of the Atomic Scientists" - Robert Jungk, translated by James Cleugh
‘Marsquakes’ could help scientists learn more about the Red Planet’s inner activity.
Let’s get ready to rumble! NASA appears to have just captured the first recording of a quake on Mars. On April 6, the seismometer on the Mars InSight lander recorded a short series of howls, grumbles and pings. One of those sounds — that grumble — is raising suspicions. It’s the first recorded sound from the Red Planet’s interior, and scientists say it’s likely a long-sought quake.
NASA released the 40-second recording on April 23. It begins with a faint, eerie howling of the Martian wind. Next comes the low rumble of the possible Marsquake. A large ping toward the end is the spacecraft’s robotic arm moving.
Explainer: Seismic waves come in different ‘flavors’
InSight landed on Mars in November 2018. Its mission is to probe the Red Planet’s interior. InSight does this by tracking seismic waves rippling through the ground. Mars lacks Earth’s powerful quakes, which are caused by shifting tectonic plates. But as the planet cools and contracts, it has smaller quakes, crackles and rumbles.
Scientists hope that InSight’s data will reveal Mars’ internal structure. That includes the size and density of its crust, mantle and core. Some of these data also might detail how heat flows through the planet’s insides as well as uncover hints of water there.
This new recording isn’t long enough to provide much insight about the Martian interior, scientists say. But it shows Mars is seismically active. It also kicks off a brand-new field of research: Martian seismology.
This is what a marsquake sounds like. A seismometer on the planet picked up three different sounds. That initial howling is Martian wind. The low grumble that follows is a possible Marsquake. Finally, the ping is the spacecraft’s moving arm.
CREDIT: Imperial College London, IPGP, CNES, JPL-Caltech/NASA
Video Clip SS255779 (Earthquake & Tsunami Generation)
Animation of the formation of an earthquake & tsunami, at a subduction zone.
A subduction zone is a region where two tectonic plates are converging, with the denser oceanic plate (left) pushed under the less dense continental plate (right). In close-up, the oceanic plate sticks on the continental plate, deforming the latter and causing a build-up of strain energy (yellow).
Eventually the force of the plate movement overcomes the friction causing it to stick, and the plate moves rapidly as the strain energy is released. This causes seismic waves to move through the crust from the focal point, or hypocenter. These waves are felt as an earthquake.
Learn More About Tectonics
The sudden displacement of the seabed also moves a huge volume of water above it, creating a tsunami. This is a vast wave that moves quickly in the open sea, with a very long wavelength and a low amplitude. When it reaches shallow water, the amplitude increases dramatically, and it comes ashore as a series of large waves, many meters in height, that reach far inland.
The combination of an earthquake and tsunami can be devastating. The quake does provide some warning about the potential tsunami, as seismic waves travel at some 25, 000 kilometers per hour, while in the open sea a tsunami wave travels at around 800 kilometers per hour.
Instruments picked up the seismic waves more than 10,000 miles away—but bizarrely, nobody felt them.
The low frequency seismic waves weren’t caused by an earthquake. “A submarine eruption could produce these low rumblings, but evidence for such an event has yet to materialize.” It’s still a mystery!
On the morning of November 11, just before 9:30 UT, a mysterious rumble rolled around the world.
The seismic waves began roughly 15 miles off the shores of Mayotte, a French island sandwiched between Africa and the northern tip of Madagascar. The waves buzzed across Africa, ringing sensors in Zambia, Kenya, and Ethiopia. They traversed vast oceans, humming across Chile, New Zealand, Canada, and even Hawaii nearly 11,000 miles away.
“These waves didn't just zip by; they rang for more than 20 minutes. And yet, it seems, no human felt them.”
“They're too nice; they're too perfect to be nature”, Anthony Lomax, an independent seismology consultant
Only one person noticed the odd signal on the U.S. Geological Survey's real-time seismogram displays. An earthquake enthusiast who uses the handle @matarikipax saw the curious zigzags and posted images of them to Twitter. That small action kicked off another ripple of sorts, as researchers around the world attempted to suss out the source of the waves. Was it a meteor strike? A submarine volcano eruption? An ancient sea monster rising from the deep?
“I don't think I've seen anything like it,” says Göran Ekström, a seismologist at Columbia University who specializes in unusual earthquakes.
However, there was no big earthquake kicking off the recent slow waves. Adding to the weirdness, Mayotte's mystery waves are what scientists call monochromatic. Most earthquakes send out waves with a slew of different frequencies, but Mayotte's signal was a clean zigzag dominated by one type of wave that took a steady 17 seconds to repeat.
So what is actually causing the super-slow vibrations at Mayotte? A submarine eruption could produce these low rumblings, but evidence for such an event has yet to materialize.
“It's like a music instrument,” says Jean-Paul Ampuero, a seismologist at the Université Côte d'Azur in France. “The notes of a music instrument—whether it's grave or very pitchy—depends on the size of the instrument.”
