The article I read announcing statewide rollout actually goes into some detail regarding what threshold the quake has to hit for notifying people. I found it interesting, because I had initially expected it to send out warnings for every quake. Some people complained that the app didn’t warn them about quakes they felt that had been quite mild, so they lowered the threshold for alert to more closely conform to people’s expectations (even though that level of shaking was very minor and not necessary to warn people about).

[0] https://www.theverge.com/platform/amp/2019/10/17/20919639/ca...