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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

#101

Post by jandrewrogers »

rcthompson wrote: post #84
jandrewrogers wrote: post #66

Earlier quoted context omitted.

You are off by about a factor of 1,000. Each incremental increase in magnitude is 10^1.5 in power. The difference between 1994 Northridge and this one is 2.1, so roughly 10^3 difference in power.

I thought that it was a log10 scale, so each increment of 1 on the scale is a 10-fold power increase, not a 10^1.5-fold.

I agree that it is not intuitive.

AFAIK, it was done that way to maintain rough congruence with historical seismic magnitude scales, which were more qualitative in nature. Modern seismic scale systems are significantly more scientific and quantitative but you can kind of retcon the historical systems if you set the exponential strength scale to 10^1.5 in the modern systems.

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

#102

Post by x______________ »

mlyle wrote: post #68
contingencies wrote: post #11

AIS map of vessels in the area: https://www.marinetraffic.com/en/ais/home/centerx:166.7/cent... A fairly small US fishing vessel is in relative proximity... https://www.marinetraffic.com/en/ais/details/ships/shipid:43... Talked to the AI which said: MMI 4.5 in the context of an M8.7 quake, for your vessel: Danger level from shaking alone: Very low in open water. Danger from tsunami in the open ocean: Very low (unless…

> That's interesting. Mental note, if piloting a vessel in a tsunami, head to deep water. E.g. the 2011 tsunami may have had a height of 1.2m or so in open ocean, but when concentrated by shallower water and a bay inlet reached 40m .

Here's a visual of your thoughts from the Fukushima event:

https://m.youtube.com/watch?v=-VcWF8dIDj4

Japan, Tsunami. Coast Guard ship rides over the tsunami waves. 日本 - 津波 4.1M views · 14 years ago

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

#103

Post by crystal_revenge »

bgwalter wrote: post #81
TylerE wrote: post #79

Earlier quoted context omitted.

Despite the common vernacular calling them "waves" they're really more like really really high tides. You're talking about something that happens over, say, 10-90 minutes, not seconds.

Again the only correct comment is downvoted. Watch Tsunamis on Youtube. The water just keeps coming and coming. They are like high tides.

> Again the only correct comment is downvoted.

I seriously wonder if people brains are being cooked these days. One of the blessing of HN used to be it was full of fairly well educated, and most importantly, curious people. Sometimes with a bit too much of a focus of the technical side of things, but at least on most technical topics the comments where a great place to get a richer understanding of a whatever was being discussed.

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

#104

Post by leptons »

idontwantthis wrote: post #76
hsbauauvhabzb wrote: post #54

Earlier quoted context omitted.

Is height the only thing that matters? Presumably 1x 2m wave is less impactful than 10 x 1m waves spread 20 seconds apart?

A tsunami is a gigantically long wave. I don’t think what you’re describing describes a tsunami.

That is not really a good description of a tsunami. Tsunamis can occur in very narrow areas too, like when landslides happen in fjords.

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

#105

Post by Kozmik1 »

supportengineer wrote: post #94

I have family members who were in Hawaii (Haleiwa) today and they are wondering if they should try to beat the tsunami and get back to their hotel in Waikiki. I am afraid Waikiki will see flooding. I know Duke's and some other restaurants were closing early.

Do not stay in Haleiwa or go to Waikiki. Consult a map, and find some uphill areas above 100ft to drive to. Drive towards Mililani and wait it out in the upland areas.

My kids are at camp right now on the North Shore and are being evacuated by bus to Mililani.

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

#106

Post by [deleted] »

decimalenough wrote: post #17

Japan forecasting tsunamis up to 3m across basically the entire eastern coast. First waves will hit within 10 minutes. https://www.nhk.or.jp/kishou-saigai/tsunami/ https://www3.nhk.or.jp/news/live/ (live, Japanese) https://www3.nhk.or.jp/nhkworld/en/live/ (live, English) The east coast is also where the vast majority of Japan's population lives, and was previously hit by the 2011 tsunami (Fukushima and all that). We'…

[deleted]

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

#107

Post by somenameforme »

TylerE wrote: post #79
hsbauauvhabzb wrote: post #54

Earlier quoted context omitted.

Is height the only thing that matters? Presumably 1x 2m wave is less impactful than 10 x 1m waves spread 20 seconds apart?

Despite the common vernacular calling them "waves" they're really more like really really high tides. You're talking about something that happens over, say, 10-90 minutes, not seconds.

This is also in many ways what makes them so deadly in places that aren't used to tsunamis. It often just looks like a regular wave or a tide that will imminently break or recede, but they never do. Here [1] is a video of one of the later waves of Thailand's 2004 tsunami.

Even worse is tsunamis are also often preceded by a 'disappearing coast' effect where the water will recede back into the ocean for hundreds of meters. This often drives tourists or locals who don't know better to go check out the sea bed and the weird behavior of the ocean, then the tsunami comes in and they're right in the middle of it.

If you're ever at a beach where the water starts rapidly disappearing, yell tsunami and get away as fast as you can. Ignore the normalcy bias, because most people, even locals, will be just standing around taking videos or even walking out into it. And don't stop running even when you're well away from the beach. It's nature's warning sign.

[1] - https://www.youtube.com/watch?v=WO7TZFBAlaE

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

#108

Post by andoando »

VintageCool wrote: post #95
bgwalter wrote: post #81

Earlier quoted context omitted.

Again the only correct comment is downvoted. Watch Tsunamis on Youtube. The water just keeps coming and coming. They are like high tides.

I remember in 2015 watching this great tsunami video at a harbor. It was about 11 minutes long. At the start, there's just a white line at the horizon. Then the fishing boats in the harbor start rocking and jangling. Then water starts pouring over some walkways and sea walls. Eventually the cameraman backs away and starts climbing a concrete tower; water starts to flood over the area where they had been standing. I t…

It never got above the boats, cant be more than a few feet tall

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

#109

Post by jychang »

rhet0rica wrote: post #39
mordechai9000 wrote: post #7

Has anyone heard how bad it was in Petropovlosk? USGS estimates "severe" shaking with the possibility of moderate to heavy damage and a chance of fatalities. They have had quite a swarm of quakes there over the last couple of weeks, including one that was M7+ around the 20th.

Severo-Kurilsk, an island town destroyed by a similar tsunami in 1956, lost its port again: https://en.wikipedia.org/wiki/Severo-Kurilsk — the rest of the settlement was rebuilt on higher ground, leaving only the port vulnerable. The settlement is notable as having belonged to the Japanese in late 19th and early 20th centuries, who once relocated islanders there. Russian Wikipedia says they were Ainu.

https://www.google.com/maps/place/50°40'00.0"N+156°07'00.0"E...

That port right next to the water has probably disappeared.

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

#110

Post by genewitch »

Arelius wrote: post #99
genewitch wrote: post #62

to put this in perspective, and please, if you work for USGS or whatever, correct me if i am wrong: this is roughly the same magnitude of the 1994 Northridge earthquake in California. i think i got the scale the wrong way around, the magnitudes reported now are only larger (than Richter) with smaller quakes compared to the Richter; it looks like 8.8ML ~= M8.8. Sorry, i looked at the chart the wrong way around.

I'm actually not sure the Northridge earthquake was cited in the Richter scale, most references I see have it as about a 6.7, which based on the USGS catalog, was it's moment magnitude 6.7 Mw https://earthquake.usgs.gov/earthquakes/eventpage/ci3144585/... And today's earthquake for comparison: https://earthquake.usgs.gov/earthquakes/eventpage/us6000qw60... And some information of Magnitude types: https://www.usgs.gov…

yeah i misread the charts, where like 3.5ML (richter) is ~5.0, and i missed that it was mb rather than ML, 8.8 ~= 6.7ish body wave magnitude.

That's the thing with standards, there's so many to choose from.

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