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.
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.
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.
https://www.fcc.gov/emergency-alert-system
But it sounds like Japan's system also sends push notifications which is why I was unclear about what you felt was different/missing. I think the specific tone sound we get from EAS is distinct.