That must be quite terrifying given the location - does the alert indicate the strength of the quake?

My alert indicated the magnitude and I received it before I felt the quake

My shakealert had a prediction of 4.9.

It does not. Not even sure it's possible.

It's highly imprecise, but not impossible. The alerts are already "this is over some threshold of ground acceleration", so there's an inherent severity estimate in the alert going out at all.

But expected intensity information isn't included because: 1) it's still a very imprecise estimate at that time, 2) actual intensity of ground motion (what you care about) will vary dramatically by location, and 3) people don't deal well with that kind of information in an alert that is really meant to be "hey, take cover".

When I was working in SF (Near Montgomery BART), there was an earthquake, but I was at the dentist at the time. The dentist was nearby on a hill near Union Square. The earthquake was not felt at all there, but it was apparently rather strong at the office down the hill.

Yikes, the idea of an earthquake striking while an active dentist's drill is in your mouth is not a pleasant thought!

Even if you could, not sure it'd be a good idea from a ux perspective.

I'm thinking the more info you provide, the longer it takes the brain to process, and split seconds matter here.

I'd also say the average person has no intuitive sense for earthquake magnitudes and giving a somewhat precise number wouldn't affect their behavior the way a broad category warning like mild, moderate, severe, and catastrophic would.

I suppose the people getting these notifications really just want to know if they should scramble for safety immediately.

"the average person has no intuitive sense for earthquake magnitudes"

probably true, but when you live in an earthquake zone you pick it up fairly quick.

for me it is sort of like

5 lots of shakes.

6 damage starts

7 lots of damage

8+ god help us all

I got a notification (in Santa Cruz) that mentioned a magnitude (4.9), a distance (~30 miles), and that I should expect mild shaking. I saw the notification a few seconds after it arrived, because my phone was making a weird noise, and the shaking started immediately after I read the notification. It was probably the strongest earthquake I have experienced in the ~5 years here, but there were several similar earthquakes every year when I was living in Chile.

If you send notifications for minor earthquakes like this, an estimate of the intensity is mandatory. At least in countries like Chile (and Japan?) where earthquakes are common. Otherwise people will learn to ignore them as false alarms.

I'm thinking the best thing to do is threshold the notifications to ~5 or above, so they're worth paying attention to, and a certain distance of course. Not an expert though. 5 is major enough to want to know isn't it?

I received the notification today for a 4.9 or something like that. It took me at least a half second to second to read the message.

I agree with your point that the message should have way less info which could buy me additional time.

Something like: 4.5-5.9: “Earthquake cat 1” 6.0-6.3: “Earthquake cat 2”

Etc. something to tell me, get ready, or something to tell me this is going to be huge, but not precise numbers or even better:

“Earthquake, 3.87 seconds” with a count down would be ideal. If I have 7 seconds I can get outside. 2 seconds and I duck and cover.

We have a demonstration that it is possible just today, as the people who got an alert also got an estimate of the strength. The broadcast estimates were slightly low: 4.8 for a 5.1. But in the neighborhood.

This is actually excellent/impressive estimate.

Remember, for this to be usable you need to start sending it out BEFORE the actual earthquake ends at the place when it is first detected.

predicted a 4.8 about 5-8sec before i felt shaking in redwood city.

Got that too, but almost at the same time when I feed it.

Stop feeding the Earth quake god damnit!

In Sunnyvale the alert hit with enough time for me to grab my mug (so it wouldn't spill on my laptop) and step away from things that could tip (TVs, bookcase, standing desk)...

Followed by a couple of tiny wobbles and then business as usual.