This is big. But it’s also offshore, pretty much directly between Cuba, Jamaica, & the Cayman Islands. And it’s a strike-slip, so tsunami risk is low.https://twitter.com/USGSBigQuakes/status/1222241341188583424 …
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People imagine tsunami as these giant curling waves that slam into a coast, each wave smaller than the last.
But they’re more like a rapidly-rising tide ebbing & inudating for hours, with the potential of ANY wave being the largest. They can be centimetres tall yet fierce.Prikaži ovu nit -
Tsunami have enormous wavelengths compared to the depth of the ocean, so mechanically they’re shallow-water waves Once we spy them, we’re very good at predicting how quickly they’ll arrive where. But measuring displacement is hard, so we don’t know height until they reach shore
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If you’re in the region and freaking out about this close call, I have excellent news! You’re about to have a region-wise tsunami training and drill on March 19, 2020 Register & learn more: https://www.tsunamizone.org/register/
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The whole region is a bit of a complicated tectonic mess. This quake was likely on the Oriente Fault, where the North America plate moves west-southwest compared to the Caribbean plate at ~1.9 cm/yr (slow but normal). It’s had large quakes in the last century, but not this largepic.twitter.com/XwC60FePw5
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Ah. Yeah. That’s a tsunami. Stay out of the water. It’s too small to chase you inland, but smaller tsunami than this have killed people who waded in.https://twitter.com/CPPGeophysics/status/1222258264265461761 …
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Q: How can a centimeter-tall tsunami kill anyone?! That’s so small you can’t even see it under noise of wind waves! A: Small tsunami don’t reach far inland (and may even be contained to the beach), but it’s still a LOT of water moving quickly. The currents are VERY strong.
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If a tsunami matches resonance frequency of an inlet or habour, it builds into a seiche. When the peaks of incoming and outgoing waves align, that constructive interference amplify wave height. Think of scooting back & forth in a tub, or driving a swing to go higher & higher.pic.twitter.com/rH5P4yVsm2
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Just like how a tsunami can match resonance frequency of an inlet, sometimes an earthquake will match resonance frequency of an earthquake. We try to design buildings to NOT match expected dominant quake frequency for a region, but that’s very tricksy.https://twitter.com/theterbush/status/1222263427193683968 …
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Q: How can such a big earthquake produce such a small tsunami?! A: Imagine you’re splashing a friend. Do you wave your arms back & forth in the water, or slam them up & down? Liquids transmit pressure waves but not shear waves. Side-to-side motion doesn’t do much.pic.twitter.com/5HygflwOeM
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Q: Which of these earthquakes are aftershocks? Are any foreshocks? Ahhhh! A: When a fault moves, it builds up stress on the locked ends. That stress redistributes as more earthquakes. But the Earth is Very Big. An earthquake only influences a radius of ~3x its fault length.
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Ready for math? The Puerto Rico earthquake swarm were happening on ~25km fault, so had an influence of ~75km. Today’s Cuba/Jamaica/Cayman Islands quake was ~1300km away. That’s Too Far. Therefore, the Puerto Rico swarm weren’t foreshocks for today’s quake. They’re unrelated.pic.twitter.com/iUUHLyZDXS
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But! Today’s M7.7 likely involved a 150+ km fault, giving it 450km radius for stress redistribution. The later M6.5 is ~200km away on the same fault: within ~3x the fault length. It’s related. Unfortunately, we only know foreshock vs aftershock retroactively.pic.twitter.com/RlOseTqTvI
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I think of aftershocks as a pile of puppies with all of them jostling around to get comfy. The number of aftershocks decays with time, just like puppies settling down to sleep. Unless someone thwack a nose. Unlikely in this scenario, but technically possible.pic.twitter.com/V7Kpdhb9In
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I’m getting pinged with mislabelled footage of prior disasters. Please be careful to assess the credibility of your sources prior to boosting sensational images or claims. Please also consider the ethics of supporting disaster porn that exploits pain.
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Q: Is it safe for me to go on my Caribbean vacation?! A: ...wanna give me your tickets? I’ll take your place! You need to make your own risk assessments and I haven’t seen an aftershock forecast, but in all likelihood we’ve already seen the biggest & worst of this sequence.
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Q: But why all these earthquakes?! A: It’s normal. You’re just paying attention this time. Every year, we get roughly 0-2 M8+, 10-20 M7, 100-200 M6, 1000-2000 M5, & even more M3 or smaller earthquakes, mostly on tectonic boundaries. Somewhere is always shaking.https://twitter.com/IRIS_EPO/status/1222319054679171077 …
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Here’s the Earth, ringing like a bell. A very, very quiet bell.https://twitter.com/geoginger/status/1223288869338210304 …
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