An Earthquake happened in SF recently where I got a push notification from Apple/iOS and I felt it maybe 5-10 seconds later. Nothing fancy though just a notification. I'm guessing it's not on for Japan? Seems like this app shows way more.
For big enough quakes you get notification from the government (a VERY loud and specific one too, being in public and hearing _everyones_ phones suddenly go off is... mildly terrifying) too; but they're so frequent and (usually) non-super-threatening that they don't get sent out for _every_ quake.
"not on for japan?" Are you expecting to have gotten a notification in SF for an earthquake in a place a 12 hour flight away? That sounds like annoyance, not a feature.
We also have the MyShake app here in CA, but I don't recall getting a notification through it for the last quake. I was asleep, though, so my memory is hazy.
All phones with 4G/5G worldwide should have it. They managed to make the broadcast push SMS thing used for the alerts a mandatory requirement for phones.
The broadcast warning from Japanese equivalent of NOAA don't get issued to areas where the peak acceleration is expected to be less than Shindo 4 level. So GP probably had 3 or less.
Shindo is peak and Magnitude is an integral, so these two can be wildly apart, and Shindo is more commonly used in Japan since buildings tend to be more resistant to longer events with lower peak intensity.