I think OP is describing a different feature. It's not a carrier feature like Amber alerts but an OS feature. Google documents this feature here: https://crisisresponse.google/android-alerts/ I'm fairly certain this is due to some Android-specific code inside GMSCore. It has nothing to do with carriers.

On iOS you have no such thing and you either rely on the carrier alert (there won't always be one) or install an earthquake alert app such as MyShake.