Tsunami warning ends for B.C. after large earthquake strikes off Alaska | Hacker News Reader

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

cbc.ca

233 pointsnergal90 comments

I felt it here in Anchorage when I was on my way to bed. It felt like a shallow, rolling earthquake. It reminded me of a quake I experienced in 2001 in Washington state. The shaking went on for what I thought was 30 seconds. My wife woke up but my kids did not.

Within a couple of minutes, I saw the reported magnitude, depth, and location on the USGS earthquake site, https://earthquake.usgs.gov/earthquakes/map/.

About the same time, Google started showing a tsunami alert: https://www.google.org/publicalerts/alert?aid=43774f005241ac...

We are in no danger from a tsunami here in Anchorage.

The alert shows potential tsunami waves arriving at coastal towns over the next couple of hours, with the first potential wave arriving in Kodiak in a few minutes. I have no idea how likely these waves are, but 7.9 is big. I am sure a lot of people are scrambling for high ground now.

God speed and be safe.

What's really wild about this is that it's actually a strike-slip earthquake, based on the focal mechanism (e.g. https://earthquake.usgs.gov/earthquakes/eventpage/us2000cmy3...) Given how big it is, I'm extremely surprised that it's stike slip. Furthermore, given the area (shallow and very near a subduction zone), anyone would immediately guess that it was a megathrust earthquake, and therefore likely to produce a tsunami. Interestingly, it's not at all.

That's likely a big part of why the tsunami watch was canceled so quickly. In addition to there being no direct detection of tsunami waves, strike slip earthquakes don't produce significant vertical movement of the seafloor (barring triggering a landslide, anyway), and therefore don't typically produce tsunamis.

However, Mw 7.9 is huge for a strike-slip earthquake. They're usually not that large. Furthermore, it's out in the oceanic crust of the incoming plate, so it's not a subduction zone earthquake at all. Instead, it's related to internal deformation of the incoming plate (albeit very near the plate boundary, so it's not exactly an intraplate earthquake either).

Large strike slip earthquakes in oceanic crust aren't unheard of, but they're quite rare. This earthquake appears similar to the large strike-slip earthquakes near Sumatra in 2012 (e.g. http://www.earthobservatory.sg/news/exceptionally-large-stri...). Definitely interesting!

A 7.9 is quite large. That is about the maximum magnitude that the San Andreas fault produces and similar in size to the 1906 San Francisco earthquake.

Since the danger seems to be receding -- I hope NWS & related agencies can use this as a good drill to fix their web properties.

Tsunami.gov couldn't handle the load, and many other official links (like mobile.weather.gov) just dump you into a government shutdown notice. Cell.weather.gov isn't even resolving.

I'm sure someone thought the critical products would still be easily available even with a government shutdown, it sure didn't work out that way.

Most of the labor contracts (not to mention ADA litigation) for the government require a certain level of service if the property is in use. With the government shut down that's not the case. It's the same reason for the infamous "this website is only available from ~9am to ~5pm" nonsense you can find on certain Social Security/IRS pages.

Why would a website go down during a government shutdown? It actually takes more work to turn it off, doesn't it?

A website can go down due to heavy load on the server/a spike in traffic.

If there's no appropriation to pay for say, hosting or electricity, you have to shut it off.

Quite honestly these agencies use it as an example of the value they provide by shutting down unnecessarily. I don’t really blame them though.

Those are probably not essential as far as the shutdown is concerned. Even NTSB investigations aren’t—there was a train crash or something during the 2013 shutdown that wasn’t investigated.

Are you sure about that? Is that the Chicago crash your talking about? The reports I was able to find indicate that the investigation did proceed but there was limited communication to the public about it because the office was closed.

https://earthquake.usgs.gov provides immediate details on earthquake activity and is my go to whenever there is an earthquake.

https://twitter.com/SF_emergency/status/955764708442714113

San Francisco Department of Emergency Management has tweeted that people within three blocks of the coast or five blocks of the San Francisco Bay should be prepared to evacuate.

Tsunami Watch for #SF. If you are w/in SF & 3 blocks of the Pacific Coast or w/in 5 blocks of SF Bay, PREPARE TO EVACUATE SO YOU ARE READY IF EVACUATION IS NEEDED. Check on neighbors who may need help. Visit http://sf72.org/hazard/tsunamis to see if you are in the evacuation zone.

We like to laugh about the Tuesday siren tests, but times like this are why we do them. If a tsunami really does hit WA and OR expect the waterfront sirens to make a pre-dawn announcement.

Tsunami watch has been cancelled for Washington, Oregon, and California.

https://twitter.com/NWSEureka/status/955777068377296896

I'm a recent newcomer to the Bay area. What is the Tsunami situation for places like Mountain View? Places like the GooglePlex are pretty close to the Bay. Is there even any real high ground in the area?? If something happens for real, do sirens sound?

Most bay area residents do not fear tsunami. The risk is low since local faults slip side to side which do not cause tsunami. A subduction fault can cause a tsunami, such as in Alaska, Japan or Chile. We would get hours of warning in such a case.

Excluding the coast and the east bay, it is not really a concern. A tsunami would have to come through the golden gate channel and make a quick turn to get to Mountain View with any strength.

The inundation map for Mountain view is here: http://www.conservation.ca.gov/cgs/geologic_hazards/Tsunami/...

And here is one for the entire bay area: http://www.conservation.ca.gov/cgs/geologic_hazards/Tsunami/...

The remainder of the inundation maps can be found here: http://www.conservation.ca.gov/cgs/geologic_hazards/Tsunami/....

Here is an animated simulation of a tsunami hitting the bay area: https://www.youtube.com/watch?v=bP_AIWgknfI

Is Twitter really the official way to notify people of danger? Or is there also a cell phone warning system?

How would they know cell phone numbers? Where I live they call landlines for emergency alerts but there's no other way to specifically target residents.

How do amber alerts work? When I lived in SF I got SF-related alerts. I don't know enough about how they work - but it sounds like tech that could be re-used for major emergency alerts.

As I should have realized, they're sent to all wireless phones in the area. On an iPhone at least both Amber and Emergency alerts are on by default but you can turn either of them off.

The state can broadcast emergency messages, it doesn't need to send them individually to some database of cell phone numbers.

Alert About Missile Bound for Hawaii Was Sent in Error, Officials Say https://news.ycombinator.com/item?id=16140761

If it was a big deal, beyond the opt-in SF text alerts, there's a thing called Wireless Emergency Alerts. It's geographically targeted. It's basically like Amber Alerts going to your phone except for imminent emergencies.

There has been some controversy about the timing and use of WEAs for evacuations for the big wildfires in California recently, but I imagine it's hard to balance alarm fatigue with the need to warn people.

There are multiple notification systems available, I find that the twitter account tends to have a lot more info about hyperlocal and situational events vs the text-based system. I've just never straight up heard the outdoor one go off except for tests.

Folks in SF that want to sign up for the texts can do so here: http://sfdem.org/public-alerts

The national and state emergency alert systems have a cellphone program. You should get cellphone alerts in an emergency (I get them for flooding, AMBER alerts, etc.).

https://tidesandcurrents.noaa.gov/tsunami/plot.html?stnid=94...

So far so good.

Could you clarify what you mean by "good" here? I see a sine wave when I click now, with an amplitude of about .75 meters.

This sine wave is expected:

https://en.m.wikipedia.org/wiki/Tide

When was the most recent ‘red’ tsunami warning for US west coast & BC? Which coastal areas were physically affected by that one?

Edit:

2005 review: https://soundwaves.usgs.gov/2005/01/fieldwork2.html

Lessons: https://pubs.usgs.gov/circ/c1187/

There's a difference between a watch and a warning.

Some buoy data: https://twitter.com/BillKarins/status/955747863140675585

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/#

Thanks, was having trouble getting it to load on my phone.

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!

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 shifted and not in GMT but 'earthquake propagation time'? Am I reading the plots wrong?

I'm probably completely wrong, but am wondering and trying to deduce the same thing. My assumption, guess really, is that they were remotely activated into "Tsunami Mode" -- a more rapid-pulse reporting mode or similar, which just is a bit noisier perhaps?

Total layman's guess though -- would love to know more if anyone knows the answer.

> My assumption, guess really, is that they were remotely activated into "Tsunami Mode" -- a more rapid-pulse reporting mode or similar, which just is a bit noisier perhaps?

That sounds like a very good guess. But then, the spikes that are purported to be the Tsunami in the media is just the ADC having a couple bad samples from being switched into a different mode or so :-)

If any USGS person is reading this thread here: Take it as a issue report that your page should be readable and understandable by lay persons, at least lay persons with a non-geophysics STEM background :D

Not an oceanic scientist but sound speed in water is ~1500m/s. This is the speed at which a pressure perturbation propagates. The speed at which the actual tsunami wave would propagate is much more slower than this. So I believe that the excitation marked in the plot is the pressure wave caused by the earthquake, which travels orders of magnitude faster than an actual water wave caused by the earth displacement.

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 reported at scheduled transmission times. When the internal detection software (Mofjeld) identifies an event, the system ceases standard mode reporting and begins event mode transmissions. In event mode, 15-second values are transmitted during the initial few minutes, followed by 1-minute averages. Event mode messages also contain the time of the initial occurrence of the event. The system returns to standard transmission after 4 hours of 1-minute real-time transmissions if no further events are detected.

The algorithm is described here: http://www.ndbc.noaa.gov/dart/algorithm.shtml

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.

Based on this page, linked by someone just above, it sounds like they do have 2-way comms (Iridium) and can remotely be put into 'Event Mode'.

http://www.ndbc.noaa.gov/dart/dart.shtml

I think it's a combo of noise when that was activated (see the page above, describes exactly what it reports when it goes into that mode, etc) -- and then for the one that shows a substantial sea level rise, it's likely just the pressure since it's all pressure-based sea-level measurement "estimates". Guess I kind of thought it measured actual rise/fall of the buoy, or maybe used GPS or something, but makes a bit more sense that it's solely based on sea-floor pressure.

This is from an aftershock, which happened 09:47:53 (UTC). Info taken from https://earthquake.usgs.gov/earthquakes/map/

The spike corresponds to about 15min delay between the quake at 9:31 UTC. But some kind of spike visible in all stations at that time, even very far away ones, like Mendocino bay.

Honestly, this looks to me rather like some bad data due to the buoys switching mode because of radio commanding 15min after the quake rather than any wave arriving. (Like the other poster suggested)

Even if the shock would travel through an Earth made out of steel, it wouldn't have reached Mendocino bay that fast.

EDIT: There is actually a time shift and it seems to be enough, as wiredfool pointed out. Thanks!

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.

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.

At the top of those pages I see this message:

> Due to the Federal Government shutdown, NOAA.gov and most associated websites are unavailable. This site will remain accessible during the federal government shutdown; however, information on the site may not be up to date and we may not be able to respond to inquiries until appropriations are enacted

so, is it up to date?

At least the time stamps in the plots seem to correspond to current time in GMT.

The Tsunami Watch for Hawaii was cancelled at 1:10am HST.

[1] http://ptwc.weather.gov/ptwc/text.php?id=hawaii.TSUHWX.2018....

All tsunami warnings and watches were cancelled at 2:12am HST / 3:12am AKST / 4:12am PST / 12:12pm GMT.

There remains a tsunami advisory in effect for South Alaska and the Alaska Peninsula.

[1] http://tsunami.gov/events/PAAQ/2018/01/23/p3054t/5/WEAK51/WE...

mirror of [1] https://gist.github.com/mckaydavis/8693d4ae9bb844f8bccef90bd...

USGS page for this quake: https://earthquake.usgs.gov/earthquakes/eventpage/us2000cmy3...

That page seems to state the magnitude was 7.9.

Looks like they just downgraded it which is common once they get more data in. Was originally reported as an 8.0.

That's a big quake! Thank God didn't cause a tsunami, although data from buoys showed VERY early on that probability was VERY low for such an occurrence. Watch for sustained wave height for serious tsunami warnings, issues coming onshore. Should you see a quick rise, sustained or increasing height offshore, then a drop... Don't wait for it! Get off the beach, away from waterways & to higher ground. I suppode those of us in California need to be on watch for the next few weeks! DutchSinse on YouTube has been working on earthquake prediction for years, and although not 100% accurate, he's been a LOT more accurate than anyone else, and has nailed the bigger quakes. I haven't taken the time to learn his methods insideout, but I've seen him call accurately numerous earthquakes. I believe with more funding, and a staff, this guy could save many, many more lives. Having worked with these buoys, and on other NOAA projects, this DutchSince guy has a method to call earthquakes early. PLEASE support him! He is the best bet to predict quakes, to tell the difference between quakes and drilling, quakes set off by drilling, etc. He's self-taught, and is more of a scientist than many I've met that went through years of "training" of methods that simply don't work. He breathes & lives this stuff, and he is onto something, far more than ANYONE else! He gets resistance from oil companies, which is sad, as he can save them money and lives! So get your batteries, your earthquake kits, Ham radios & be ready! Stay safe, always be prepared & ready for any type of disaster! Stay safe!

In case you're wondering whether an Alaskan earthquake could cause damage in California, the answer is yes. The tsunami from the 1964 Good Friday earthquake in Alaska obliterated the port of Crescent City:

https://en.wikipedia.org/wiki/Crescent_City,_California#Tsun...

I hope everything is okay - but I’m finding this a fascinating real-time case study of the chaotic nature of breaking information during a (potential) disaster. Conflicting reports, false alarms, difficult-to-parse data...

And a number of false-but-believable tweets by people, I presume for the attention. E.g. "Harbor X is emptying", or "Wave now 60ft high!"

There was a study done a while back basically demonstrating that following breaking news too closely actually resulted in a less accurate recollection of the facts. Turns out it’s difficult to forget compelling information even if it ultimately proves to be false (and you’re aware that it’s false).

Source?

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

Times for Alaska:

Estimated tsunami start times for selected sites are;

Kodiak Alaska 145 AM. AKST. January 23.

Elfin Cove Alaska 150 AM. AKST. January 23.

Seward Alaska 155 AM. AKST. January 23.

Yakutat Alaska 200 AM. AKST. January 23.

Sitka Alaska 200 AM. AKST. January 23.

Langara British Columbia 210 AM. AKST. January 23.

Valdez Alaska 215 AM. AKST. January 23.

Cordova Alaska 220 AM. AKST. January 23.

Sand Point Alaska 220 AM. AKST. January 23.

Unalaska Alaska 240 AM. AKST. January 23.

Homer Alaska 250 AM. AKST. January 23.

Craig Alaska 300 AM. AKST. January 23.

Cold Bay Alaska 300 AM. AKST. January 23.

Adak Alaska 305 AM. AKST. January 23.

Tofino British Columbia 340 AM. AKST. January 23.

Shemya Alaska 345 AM. AKST. January 23.

Saint Paul Alaska 400 AM. AKST. January 23.

Source: http://forecast.weather.gov/wwamap/wwatxtget.php?cwa=usa&wwa...

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?

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.

You can also quickly access this info at http://www.tsunami.gov. Or at least normally it's quick; page is taking a good 10 seconds to load for me right now—under a bit of load, presumably.

It includes Canada as well. (In fact, the BC Emergency site quotes from it and links back to it!)

I know but since tsunami.gov it's getting is getting hammered I figured out it's better to leave their bandwidth for people in risk rather than hit them with the HN frontpage effect.

The servers/pipes at tsunami.gov are clearly grossly underpowered for their intended use.

Hopefully, they'll be able to get some equipment upgrades as a result of this.

I wonder what their infrastructure looks like. This is the poster case for a scalable cloud setup. 99%+ of the time their traffic is probably nearly zero, and when there will be a significant spike it's generally going to be predictable!

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.

Victoria is a better target city. Vancouver is sheltered by Vancouver Island where Victoria is considerably more exposed.

Kodiak Police Department 7 mins · TSUNAMI UPDATE: 0229 hours

Harbor officers report water reciding from our harbor. Citizens should remain in place and wait for further updates.

https://www.facebook.com/KodiakPD/

> Tsunami warning ends for B.C. after large earthquake strikes off Alaska I first interpreted this as “There was going to be a Tsunami, but then an earthquake struck which nullified it.”

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

Slower than the speed of sound in water, but still very impressive

Faster than an airplane though.

Perhaps, the arc distance traveled for the wave is a smaller than the plane's. The plane is flying 10Km in the sky.

The difference in arc lengths is less than you'd think--

It's only about 20km further assuming Alaska is 1/3 of the world's circumference away from Australia.

  (1/3)*(2*pi*(r+10) - 2*pi*r) = (1/3)(20*pi) ~= 20

Wow, that is surprising. I should have thought about it further. The radius of earth is 6371Km and 10Km works out to be 0.15% of it. So 20Km is reasonable.

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)

It will absolutely affect boats in the Pacific.

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.

Well, those waves have nothing to do with the earthquake anyway, and they aren't traveling at the speed of a jet plane :)

The disturbation will be less than 1 meter at open. The actual wave gains altitude only when it hits the shallow waters.

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.

Yeah, no more than a bit of swell does though. Best example I can find is this -> https://youtu.be/ZS6EmSxncz4?t=78

would tsunami be a concern for Californians when a big earthquake happens in California?

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