[cossatot]

Based on the location and focal mechanism of the earthquake (https://earthquake.usgs.gov/earthquakes/eventpage/nc75095651...), this is a strike-slip earthquake on the plate boundary between the Pacific and Gorda/Juan de Fuca plates. Strike-slip earthquakes occur when two plates slide beside each other during an earthquake, usually along a steeply-dipping if not vertical fault. These kinds of earthquakes almost never produce damaging (or even really noticeable) tsunamis because there is no real displacement of sea water by seafloor movement, unlike a thrust or subduction zone earthquake.

The USGS's automated systems calculate the location and focal mechanism/moment tensor pretty much instantly from the seismic network. The system should know that a significant tsunami is unlikely based on the parameters of the earthquake. On the one hand, it's good to be cautious, but on the other hand, a system designed to cry wolf is also self-undermining. Maybe they should have a tiered warning system?

[rz2k]

Doesn't any earthquake, regardless of fault type increase the immediate risk of a submarine landslide?

There are many steep canyons on the Pacific coast, and here is just one example of mass casualties from a tsunami resulting from a submarine landslide triggered by a strike-slip fault earthquake:

Caltech, 2018[1]: "Contrary to Previous Belief, Strike-Slip Faults Can Generate Large Tsunamis"

[1] https://www.caltech.edu/about/news/contrary-to-previous-beli...

[cossatot]

Yes, the probability of tsunamogenic landslides do increase during earthquakes, but it's still quite unlikely for an event of this magnitude tens of km from the continental slope; this is why a properly-calibrated tiered system would be better.

The reason that the Palu event is so notable is precisely because it's uncommon. It's also a very different system: the causative fault is running along the axis of a shallow bay that is only a few km across, so even if the landslide did occur, rapid movement of the steep, shallow coastlines would surely have generated a smaller tsunami. It's a geographical and tectonic situation in which at least a minor tsunami is expected a priori conditional upon an earthquake, so a warning system would account for that in principle. (In practice there isn't time enough to mobilize because the tsunami hits while the ground is still shaking). The bay at Palu is like a somewhat larger Tomales bay--an earthquake right there is going to make some waves. Very different situation than one far off shore.

[dragonwriter]

> Yes, the probability of tsunamogenic landslides do increase during earthquakes, but it's still quite unlikely for an event of this magnitude tens of km from the continental slope; this is why a properly-calibrated tiered system would be better

There is a tiered system, its calibrated based on a combination of magnitude and warning time for the initial alerts (updated notices are based on other measurements and observations, but if gathering and analyzing observations before an initial warning doesn't leave time to act on it, it doesn't matter how accurate the warning is.)

[gosub100]

Those can even happen in bodies of fresh water. There's evidence of one at Lake Tahoe discovered by robot submersibles.

[dataviz1000]

I've been subscribing to tsunami warning system emails since the mid or late 2000s. They send the first email about the earthquake as a warning that something happened. Then after ,if a tsunami isn't detected they send an email saying that. If there is a tsunami they will send the first warning and as soon as sensors and satellites start to track the wave they will update at intervals with a table of expected arrival times and magnitude or height. So, yes, they send a warning that something happened, then they send information if there is a threat.

Here is an example of the first message sent 9 minutes after 2011 Tōhoku earthquake https://imgur.com/a/1mwAKqc.

[LeoPanthera]

> The USGS's automated systems calculate the location and focal mechanism/moment tensor pretty much instantly from the seismic network.

According to a USGS guy on the news just now, this isn't true. They know the location, and the magnitude, but the moment tensor takes time. Therefore any ocean earthquake 7.0 or above triggers an immediate tsunami warning.

[0xffff2]

Looking at https://tsunami.gov/, it seems like they do have a 4 tier system, but they jumped straight to the highest tier in this case?

[throw83838]

HN has good SnR generally, but I would default to trusting their automated system more than Random Internet Guy. Even if the warning gets canceled after measurements become available.

[cossatot]

I'm a Random Internet Guy who is a professional in the field (earthquake hazards, not tsunamis in particular).

[rootusrootus]

You definitely sound like it. But man, I've met some convincing liars online so I try to be cautious when someone makes claims and I have no proof that they are who they claim to be (especially when they didn't make that claim explicitly, and just sound very intelligent).

It's a complication that will never happen, but sometimes I think it would be cool if HN had a way of authenticating experts and giving them flair. So many legit smart people here.

[misswaterfairy]

Based on the travel time map, and that the earthquake event was just 45 mi SW of Eureka, CA (and potentially closer to the coastline elsewhere), it seems that jumping straight to Tsunami Warning is the most appropriate messaging, given that the expected time to impact is quite short?

https://www.tsunami.gov/events/PAAQ/2024/12/05/so1aq0/1/WEAK...

(Some of my job requires me to deal with natural disaster public warnings; but not tsunami specifically)

(I'm late to the party. The warning has since been cancelled: https://www.nbcbayarea.com/news/california-earthquakes-tsuna...)

[jerlam]

It's a three-tier system, I was confused when I was looking at it. The fourth item is "threat" which you would think is higher than "warning", but "threat" is only used outside of the US.

[teaearlgraycold]

The system is training me to ignore it already. I’m in SF and we had a flash flood emergency alert. I never heard of or saw any floods. I could believe a street or two might have had a few inches of water at most. But honestly I’d bet against even that.

And then there’s this tsunami alert today.

[taatof]

> I never heard of or saw any floods.

There was a ton of flooding on flat roads and highways during the last week+ long storm session. I saw several lanes impassable on 101, and several spots in SF where a car could easily have gotten flooded.

All the alerts I got were basically "please don't drive" and not "you're gonna die!", which I think is totally reasonable.

[wbl]

SF topography means some places like the Mission and Dogpatch can have severe floods and the rest be fine.

[crazygringo]

Flash floods depend on your elevation.

I've gotten the warning and my street is perfectly fine... and then I look at social media and cars on the street are half-submerged just 20 blocks away.

You might not even be aware of elevation differences when they're gradual.

[s1artibartfast]

It is also unclear to me how someone is supposed to differentiate a real emergency from an "Extreme threat/danger" and what authority they should look to, besides their common sense.

I guess people can go on twitter and read some random posts.

[bsder]

Flash flood alerts are one of the few that I don't get annoyed about seeing. A big rain up in the mountains can result in a huge chunk of water somewhere downstream a couple of hours later. This significant displacement of time and space between cause and effect warrants caution and notification.

[anyfoo]

One superfluous tsunami warning after an outlier 7.0 earthquake, and already "the system is training [you] to ignore it"?

[sib]

This is similar to the "severe weather alert" I just received on my phone when the temperature will range from 47' to 67' F (8' to 19' C) in Los Angeles today, December 5, with clear, sunny skies and no noticeable winds.

Of course, when I tap on the notification and open the app, I see that it's actually driven by an air quality alert because the AQI will be 112 (which isn't even that high.)

Come on guys - the dictionary defines weather as, "the state of the atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness."

[caseyf7]

Also confusing when the SF Fire captain is on the radio telling people to evacuate to 100 ft above sea level right after a CalTech seismologist says it is unlikely to cause much of a tsunami due to being a strike-slip earthquake.

[bglazer]

Totally off topic, but is your name a reference to the Cossatot River in Arkansas? If so, fantastic choice.

[cossatot]

Yes, it's a big one in my formative years as a kayaker. I've used the handle in a lot of places and I think you're the first person that's recognized it.