The tsunami that vibrated through the entire planet and no one saw

September 14, 2024 3:35 PM

The Conversation: Earthquake scientists detected an unusual signal on monitoring stations used to detect seismic activity during September 2023. We saw it on sensors everywhere, from the Arctic to Antarctica. We were baffled – the signal was unlike any previously recorded. Instead of the frequency-rich rumble typical of earthquakes, this was a monotonous hum, containing only a single vibration frequency. Even more puzzling was that the signal kept going for nine days.

Science article: A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days

posted by ShooBoo (7 comments total)

Wow, that would have been fascinating to work on. I imagine it might have been a lot more observable and 'interesting' had the fiord been differently shaped. Local scientists got pretty lucky with the small amount of equipment loss. I imagine we might be seeing more of these types of things.
posted by BlueHorse at 4:01 PM on September 14

Heard one of the authors discussing this on BBC radio a day or two ago. He said that there had been a cruise ship in the fjord the day before it happened.
posted by rory at 4:53 PM on September 14 [2 favorites]

I'd read something about this a couple days ago, but the video embedded in the first post link's article did a great job of helping me understand exactly what was going on.
posted by Greg_Ace at 6:58 PM on September 14

Thank you!

Here's that video with the authors explaining it.
posted by intermod at 9:37 PM on September 14 [4 favorites]

I am most surprised by the speed of the propagation of the seismic shockwave. If I understand their video properly, the seismic wave propagated from its origin in Greenland all the way to Antarctica in less than an hour.

If the wave traveled at something more than 10,000 mph that just seems crazy. Or at any rate not what I would have expected at all.
posted by Nerd of the North at 1:40 AM on September 15

Seismic velocity varies , but it depends on density , i.e. depth of propagation.
In the crustal layers seismic velocity is approximately 7 kilometers per second or 7 * 60* 60 =
25200 kilometers per hour or approximately 15000 mph.
Speed is less in sedimentary layers, approximately 2-4 km per second.
These waves will arrive later in the record
The seismic record is a record of a series of events with different arrival times
Waves propagating in the unconsolidated material near surface are very slow
posted by yyz at 5:39 AM on September 15 [9 favorites]

Compressional wave (P wave) speed is just the 'speed of sound', which depends on the medium. Its faster in rock than air, and certain rocks over others (as yyz points out). Roughly 20-25x faster: 0.3 km/sec for air, ~7 - 8 km/sec for crust and mantle rocks. A plane trying to keep track would have to go Mach 25 or greater (more because the plane has to take a longer path)!
posted by bumpkin at 5:56 AM on September 15 [3 favorites]