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M8.7 earthquake in Western Pacific, tsunami warning issued

earthquake.usgs.gov

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Re: M8.7 earthquake in Western Pacific, tsunami warning issued

#231

Post by K0balt »

ninetyninenine wrote: post #167
K0balt wrote: post #150

Earlier quoted context omitted.

The difference is that people know what 2m (wind driven) waves look like at their cities seawall. A 2m tsunami is a -completely- different phenomenon, because of its length. Depending upon the underwater geography, a 2m tsunami might flood right over their 3m seawall, and wipe out entire parts of the city, sweeping hundreds of people out to sea. A 2m wind wave will get saltwater spray on cars driving by. They are bot…

I think you’re out of touch. A tsunami is a wave both from a pedantic perspective and an intuitive one and most people aren’t deceived into thinking that tsunamis aren’t dangerous at all because it’s a wave. That’s just made up garbage. You’re like coming up to me and saying hurricane is not wind because it’s dangerous to think of a hurricane as only wind. Dude. Nobody is thinking hurricanes are just chill just becau…

So, I’m sorry that I evidently didn’t manage to convey my point effectively. The problem is that wave is accompanied by a measurement that deceptively buries the lede.

Everyone knows hurricanes are wind. So they look for the wind speed to understand the threat. And it’s effective at characterizing the threat. A 100mph wind is going to be similarly destructive as any other 100mph wind. It works and is semantically and linguistically accurate.

Everyone knows a tsunami is a wave, and it is a strong intuition to believe that a wave is defined by its height. , and the height of the tsunami is actually one of the most widely reported metrics. But intuition about the effects of a tsunami by wave height is dangerously wrong. A tsunami is not at all similar to the vast, vast majority of waves in character and effect. Its speed and length at way, way out of band, and are seldom reported.

Re: M8.7 earthquake in Western Pacific, tsunami warning issued

#232

Post by ninetyninenine »

Tor3 wrote: post #169
ninetyninenine wrote: post #130

Earlier quoted context omitted.

These things are 100% waves. It's not a misnomer. It fits the scientific definition of waves and it fits our intuition of what waves are. These are NOT tides. https://www.noaa.gov/explainers/science-behind-tsunamis

A tsunami absolutely does not fit our intuition of what waves are. It looks like a wave. But it does not stop. It just continues. That little wave goes on an on, farther and farther inland. After an hour it may still go on. It's a nightmare wave, because it doesn't not fit one's intuition of what waves are.

>It looks like a wave.

and it IS a wave. I don't understand the resistance here. It BOTH is a wave and looks like a wave.

But because it does not stop, it is not a "wave". Let's just stop with the strange pedantism.

Re: M8.7 earthquake in Western Pacific, tsunami warning issued

#233

Post by K0balt »

chimeracoder wrote: post #159
K0balt wrote: post #140

Earlier quoted context omitted.

Yes, they are waves, but they are often very long waves. A typical 1m wave might be 20m long. A tsunami wave might be a kilometer long or longer. That is why people say they are like a tide. The wave arrives, then does not recede for several minutes. So, while a 4m wind driven wave might break over a seawall and even wash a car off the road, a 4m tsunami washes ships over that same seawall and floods the city. It’s a…

> I’ve been at sea when a 3m tsunami passed, we barely felt it. How far out at sea were you? And how did you know at the time?

We were about 50 miles offshore, off the continental shelf (in very deep water) we got the information of the wave from our regular meteorological diligence, since it was my job to get our satellite weather and any notices to mariners on a 6 hour rotation.

I saw the wave on radar first, since it lifted ships that were below our horizon up to where they could be seen again for a few sweeps. But it just felt like A gentle lifting. I didn’t even feel the subsidence of the wave. Interestingly, ships 20 miles away from us but near the edge of the shelf reported isolated severe and chaotic waves.

Re: M8.7 earthquake in Western Pacific, tsunami warning issued

#234

Post by K0balt »

fc417fc802 wrote: post #204
K0balt wrote: post #150

Earlier quoted context omitted.

The difference is that people know what 2m (wind driven) waves look like at their cities seawall. A 2m tsunami is a -completely- different phenomenon, because of its length. Depending upon the underwater geography, a 2m tsunami might flood right over their 3m seawall, and wipe out entire parts of the city, sweeping hundreds of people out to sea. A 2m wind wave will get saltwater spray on cars driving by. They are bot…

I appreciate your effort to provide an understandable explanation. That said, in context the original statement was so extremely misrepresentative of the reality that I felt it left the realm of "inaccurate but effective for communication". I certainly didn't see the objections as pedantic.

A clarification was appropriate because it really did miss the physics, but doubling down on the definition of wave without talking about speed, length, and volume (which is what had confused OP in the first place) was not only suboptimal in teaching useful knowledge to OP, it was also misleading in a way that could (and did, in at least one case of a commenter in this thread) lead to a dangerous misconception about characterising tsunamis.

Perhaps it wasn’t intentionally pedantic, but the way that it was doubled down on later makes me suspect an argument in bad faith, or at least an epic case of missing the opportunity to usefully inform.

I value this site for the general character of people trying to educate more than just troll, and I think it’s important to try to educate trolls as well to understand a more constructive and respectful way to interact here. Ostensibly, we take off our clown shoes and leave them at the door.

OTOH I may have read multiple comments in similar tone that were not all attributed to one poster , giving me a mistaken impression of the intent. In that case, I owe an apology for perhaps overreacting.

Re: M8.7 earthquake in Western Pacific, tsunami warning issued

#235

Post by bee_rider »

decimalenough wrote: post #116
timr wrote: post #90

Earlier quoted context omitted.

My favorite is the NHK reporters standing in the middle of absolutely nowhere with their NHK helmets. No matter what the event, there is a reporter wearing a helmet.

Also, the very first thing they say when the camera cuts to them is that they are standing in designated evacuation zone X that's Y meters above sea level. Then the cameraman zooms at the ocean, which is blurry and shaky because they're in the designated evacuation zone Z km away from the coast.

That’s probably the responsible thing to do. It is always odd to see American weather disaster reporters, like:

“We’re here inside the hurricane, let me go outside so you can see that the wind will push me over. Can’t hear anything because my microphone is getting blasted by the wind. Over there you can see the emergency responders, they appear to be fleeing. Tell my wife I love her, but I’ve got to die for some b-roll.”

Re: M8.7 earthquake in Western Pacific, tsunami warning issued

#237

Post by golem14 »

ninetyninenine wrote: post #114
crystal_revenge wrote: post #98

Earlier quoted context omitted.

I'm surprised so many people don't understand what tsunamis are. It's a "wave" created by a sudden shift in the Earth's crust. Imagine, suddenly, water on each of side of that split is now at different heights and has to equalize. It's much closer to just removing a dam that is holding back water equal in height to the new difference between the sea floors. What you get is not a "wave" but a wall of water.

This doesn't make sense to me intuitively. It must be a wave. Imagine you have a fault line. There is a left side and a right side to the fault line. If the left side lowers with a shift then that shift MUST be localized to the area around the fault. Because if it wasn't then that means there's an elevation change across the board for everything to the left of the fault. You see how that doesn't make sense? So if the…

Maybe the easiest way is explain it by volume of water coming at you. A 'normal' wave comes at you for maybe 2-5 seconds, then recedes. A tsunami wave might come at you for what, a few minutes? So moves more than 20x-50x the water than an equivalent 'normal' wave, which has no other way to go?

Re: M8.7 earthquake in Western Pacific, tsunami warning issued

#238

Post by bee_rider »

jancsika wrote: post #145
ninetyninenine wrote: post #114

Earlier quoted context omitted.

This doesn't make sense to me intuitively. It must be a wave. Imagine you have a fault line. There is a left side and a right side to the fault line. If the left side lowers with a shift then that shift MUST be localized to the area around the fault. Because if it wasn't then that means there's an elevation change across the board for everything to the left of the fault. You see how that doesn't make sense? So if the…

Since we're intuiting, I'm just imagining something like quickly adding a "D.C. offset" of some given height to the crests and troughs you'd measure by sampling ocean waves. In fact, I'm not sure I should have quotes around that. Isn't your interlocutor saying a tsunami is literally a direct current of water flowing toward the shore?

I guess it is like a step function, or at least a step function on one side and a really long decay on the other. Is a step function a wave? I’m not sure, my signal processing class was too early in the morning. Maybe it depends on who you ask, mathematicians vs engineers. I’ll go along with the ones that might make a taser or something.

Re: M8.7 earthquake in Western Pacific, tsunami warning issued

#240

Post by ccozan »

msephton wrote: post #228
pezezin wrote: post #210

Earlier quoted context omitted.

I do live in Japan and good god, I have never seen such messy people anywhere else in the world. The offices of all my Japanese colleagues are piles upon piles of documents and boxes without any kind of order. But the cities themselves are like that. There is zero urban planning, just buildings thrown around in impossible non-Euclidean patterns.

They're a book from the early 1990s called "Tokyo Style" that is packed with photos of real living conditions from back then. Chaos of every variety. Plus some Super Famicom and PC-Engines laying around. A very cool book, most recently reprinted in 2024 with Japanese/English captions.

and the cables, the cables hanging from everywhere!

( btw, has anyone noticed in anime there are always frames of street cabling? Like those cylindrical transformes and thick cables. Almost cyberpunk! )

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