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Tsunami warning ends for B.C. after large earthquake strikes off Alaska

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Re: Tsunami warning ends for B.C. after large earthquake strikes off Alaska

#41

Post by wiredfool »

onnoonno wrote: post #19
JorgeGT wrote: post #8

Earlier quoted context omitted.

Link to the actual buoy data page: http://www.ndbc.noaa.gov/station_page.php?station=46410&type... Worth noting that other nearby buoys don't show such a dramatic wave: http://www.ndbc.noaa.gov/station_page.php?station=46409&type... Here's a map: http://www.ndbc.noaa.gov/obs.shtml (click on the blinking ones) And here's a map of tsunami-capable tide stations: https://tidesandcurrents.noaa.gov/tsunami/#

What I don't get is that nearly all the buoys that have that moving icon "Tsunami alert" show some excitation at the ~9:45GMT mark. But I would of course expect the buoys that are farther away to only show some kind of peak when the wave actually reaches them. And it looks like they are thousands of km away, so some of them should not even have been reached yet. Some what is going on there? Is the data time actually…

IANA Tsunami guy, but I worked with them in college.

The water column height on these buoys is a pressure transducer on the floor of the ocean (http://www.ndbc.noaa.gov/dart/dart.shtml)

The time skew of the events is small, but does exist. They're all within minutes of the 9:31am gmt earthquake, getting longer as you get away from the epicenter. i.e, way faster than a tsunami travels, but about how fast an earthquake travels. (Earthquakes spread in x miles per second, tsunamis in x miles per minute)

I _think_ what you're seeing is the pressure sensor picking up the earthquake and converting it to a water column height.

Re: Tsunami warning ends for B.C. after large earthquake strikes off Alaska

#42

Post by onnoonno »

JorgeGT wrote: post #33
onnoonno wrote: post #28

Earlier quoted context omitted.

But that doesn't fit the data, either. The buoys all report something around the 9:45ish GMT mark. And 1500m/s would mean you reach Mendocino bay in California only about now or so. But have a look at the plot: https://archive.fo/KsN8b

That's true. Maybe when a buoy registers an "event", an "snapshot" of more fine-grained 15-sec data is recorded from all DART buoys? Edit. From this page: http://www.ndbc.noaa.gov/dart/dart.shtml > The system has two data reporting modes, standard and event. The system operates routinely in standard mode, in which four spot values (of the 15-s data) at 15-minute intervals of the estimated sea surface height are repor…

I see, thanks. But that rather sounds like the buoy itself is switching modes?

From the look of all the plots, even the far-away ones, it rather looks to me like they have been remotely switched into event mode (with that 15s stuff being plotted at about the same time)?

I guess I am really confused about the time stamps.

Re: Tsunami warning ends for B.C. after large earthquake strikes off Alaska

#44

Post by mattnewport »

porker wrote: post #16
yread wrote: post #10

The tsunami alert: http://ptwc.weather.gov/ptwc/text.php?id=hawaii.TSUHWX.2018.... IF TSUNAMI WAVES IMPACT HAWAII THE ESTIMATED EARLIEST ARRIVAL OF THE FIRST TSUNAMI WAVE IS 0423 AM HST TUE 23 JAN 2018

Do you know why these reports mention Hawaii, rather than (say) Vancouver and other coastal cities nearer to the epicenter, where I would imagine a tsunami would reach first?

Vancouver is well protected from tsunamis caused by earthquakes in most spots (including this one) by Vancouver Island. The Greater Vancouver tsunami zone is the only one in BC not covered by the tsunami warning issued for this quake.

Re: Tsunami warning ends for B.C. after large earthquake strikes off Alaska

#45

Post by wiredfool »

kijin wrote: post #36
Jedi72 wrote: post #27

Earlier quoted context omitted.

Will this wave affect boats? Imagine being on a yacht in the middle of the Pacific (not Atlantic Doh!) when a 10m wave moving at 20m/s hits (figures not accurate just guesses)

There probably won't be 10m waves in the middle of the ocean. The waves will only be a few inches tall, but moving FAST. Then they get dramatically taller as they are forced to slow down in shallow water.

This is the North Pacific in Winter. I'd be surprised if there weren't 10m waves out there.

Re: Tsunami warning ends for B.C. after large earthquake strikes off Alaska

#46

Post by onnoonno »

wiredfool wrote: post #41
onnoonno wrote: post #19

Earlier quoted context omitted.

What I don't get is that nearly all the buoys that have that moving icon "Tsunami alert" show some excitation at the ~9:45GMT mark. But I would of course expect the buoys that are farther away to only show some kind of peak when the wave actually reaches them. And it looks like they are thousands of km away, so some of them should not even have been reached yet. Some what is going on there? Is the data time actually…

IANA Tsunami guy, but I worked with them in college. The water column height on these buoys is a pressure transducer on the floor of the ocean ( http://www.ndbc.noaa.gov/dart/dart.shtml ) The time skew of the events is small, but does exist. They're all within minutes of the 9:31am gmt earthquake, getting longer as you get away from the epicenter. i.e, way faster than a tsunami travels, but about how fast an earthqua…

Oh you are right. It actually _does_ have a time shift. I take back what I said and assert the opposite!

Thanks for the explanation.

Re: Tsunami warning ends for B.C. after large earthquake strikes off Alaska

#47

Post by wiredfool »

Jedi72 wrote: post #27
mathgenius wrote: post #12

Wow 15 hours to australia, that thing is moving fast.

Will this wave affect boats? Imagine being on a yacht in the middle of the Pacific (not Atlantic Doh!) when a 10m wave moving at 20m/s hits (figures not accurate just guesses)

Picture a 1m high wave with a crest to crest wavelength of 100km. That is pretty much what an open water tsunami looks like.

This is why when there's a tsunami warning, boats are supposed to leave the harbor, where it's dangerous, and get to sea where they won't notice the wave.

Re: Tsunami warning ends for B.C. after large earthquake strikes off Alaska

#48

Post by z3t4 »

wiredfool wrote: post #11
JorgeGT wrote: post #8

Earlier quoted context omitted.

Link to the actual buoy data page: http://www.ndbc.noaa.gov/station_page.php?station=46410&type... Worth noting that other nearby buoys don't show such a dramatic wave: http://www.ndbc.noaa.gov/station_page.php?station=46409&type... Here's a map: http://www.ndbc.noaa.gov/obs.shtml (click on the blinking ones) And here's a map of tsunami-capable tide stations: https://tidesandcurrents.noaa.gov/tsunami/#

I'd be _really_ suspicious of data showing a 10M tsunami in the open ocean. In deep water, they're super long wavelength low amplitude waves, it's only when they interact with the bottom that the wave piles up and gets to large amplitude.

yeh, that would be like over 100m when it hits shallow water. But if the water level is unusually low then GTFO!

Re: Tsunami warning ends for B.C. after large earthquake strikes off Alaska

#49

Post by diasporic »

porker wrote: post #18
JorgeGT wrote: post #17

Earlier quoted context omitted.

The page is specific to Hawaii, but you can go to http://www.weather.gov/ and in the map, click your region and then "tsunami warning" or "tsunami watch" to see estimated times for other states. This is the tsunami watch notice for coastal areas of Oregon, Washington & California: http://forecast.weather.gov/wwamap/wwatxtget.php?cwa=sew&wwa...

Thanks. I hadn't realised that these pages would exclude the coast of Canada either, and they'd have their own site. https://weather.gc.ca/warnings/index_e.html

https://www.emergencyinfobc.gov.bc.ca/tsunami-warning-coasta...

This British Columbia government webpage includes the tsunami watch locations and time estimates for Canadian locations PLUS information from the same source as the USGS webpage.

Cut-n-paste to reduce their server load (but check directly later for updates. Stated update frequency is 30 minutes):

UPDATE: Tsunami Warning: coastal areas of BC following 7.9M earthquake in Gulf of Alaska. Jan. 23, 2018 at 02:08AM January 23, 2018 at 2:57 am

This information is preliminary and may change rapidly. Listen to local officials and visit National Tsunami Warning Center for more information. Update: revised magnitude Tsunami Warning REMAINS in Effect for; * BRITISH COLUMBIA, The Juan de Fuca Strait coast, the outer west coast of Vancouver Island, the central coast and northeast Vancouver Island, and the north coast and Haida Gwaii * SOUTHEAST ALASKA, The inner and outer coast from The BC/Alaska Border to Cape Fairweather, Alaska (80 miles SE of Yakutat) * SOUTH ALASKA AND THE ALASKA PENINSULA, Pacific coasts from Cape Fairweather, Alaska (80 miles SE of Yakutat) to Unimak Pass, Alaska (80 miles NE of Unalaska) * ALEUTIAN ISLANDS, Unimak Pass, Alaska (80 miles NE of Unalaska) to Attu, Alaska including the Pribilof Islands Tsunami Watch REMAINS in Effect for; * CALIFORNIA, The coast from The Cal./Mexico Border to The Oregon/Cal. Border including San Francisco Bay * OREGON, The coast from The Oregon/Cal. Border to The Oregon/Wash. Border including the Columbia River estuary coast * WASHINGTON, Outer coast from the Oregon/Washington border to Slip Point, Columbia River estuary coast, and the Juan de Fuca Strait coast PPRELIMINARY EARTHQUAKE PARAMETERS – UPDATED ——————————————- * The following parameters are based on a rapid preliminary assessment and changes may occur. * Magnitude 7.9 * Origin Time 0032 AKST Jan 23 2018 0132 PST Jan 23 2018 0932 UTC Jan 23 2018 * Coordinates 56.0 North 149.1 West * Depth 12 miles * Location 175 miles SE of Kodiak City, Alaska 360 miles S of Anchorage, Alaska FORECASTS OF TSUNAMI ACTIVITY —————————– * Tsunami activity is forecasted to start at the following locations at the specified times. FORECAST START SITE OF TSUNAMI —- ———- * Alaska Kodiak 0145 AKST Jan 23 Seward 0155 AKST Jan 23 Elfin Cove 0155 AKST Jan 23 Sitka 0200 AKST Jan 23 Yakutat 0205 AKST Jan 23 Valdez 0215 AKST Jan 23 Sand Point 0220 AKST Jan 23 Cordova 0225 AKST Jan 23 Unalaska 0240 AKST Jan 23 Homer 0255 AKST Jan 23 Craig 0300 AKST Jan 23 Cold Bay 0300 AKST Jan 23 Adak 0305 AKST Jan 23 Shemya 0350 AKST Jan 23 Saint Paul 0400 AKST Jan 23 * British Columbia Langara 0210 AKST Jan 23 Tofino 0340 AKST Jan 23 * Washington Neah Bay 0455 PST Jan 23 Long Beach 0500 PST Jan 23 Moclips 0500 PST Jan 23 Westport 0510 PST Jan 23 Port Angeles 0530 PST Jan 23 Port Townsend 0555 PST Jan 23 * Oregon Port Orford 0505 PST Jan 23 Charleston 0510 PST Jan 23 Seaside 0510 PST Jan 23 Newport 0515 PST Jan 23 Brookings 0515 PST Jan 23 * California Crescent City 0520 PST Jan 23 Horse Mountain 0525 PST Jan 23 Fort Bragg 0525 PST Jan 23 Monterey 0555 PST Jan 23 San Francisco 0620 PST Jan 23 Port San Luis 0620 PST Jan 23 Santa Barbara 0635 PST Jan 23 Los Angeles Harb 0650 PST Jan 23 Newport Beach 0700 PST Jan 23 La Jolla 0705 PST Jan 23 Oceanside 0705 PST Jan 23 OBSERVATIONS OF TSUNAMI ACTIVITY ——————————– * No tsunami observations are available to report.

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