You always need to act on it. Get an earthquake alert? Run outside. You can go back if it was a false alert.

In Mexico City the seismic alert gives like a minute (sensors are on the coast off Guerrero 350km away). Communities closer to the usual epicenter get almost no warning.

Before one can action one needs time to read and process whether the alert is for earthquake, tsunami, child abduction, etc

Those things could be solved with better UI (pictures, colors, ..) to see on one glance what is going on.

First word of the alert : EARTHQUAKE. What do you do?

There are no tsunamis in Mexico City haha

I don't see the point of focusing the conversation on Mexico City. You may be far enough from the fault line to have plenty of time to react, but not everyone does (as you acknowledge). You may not have tsunamis, but that doesn't change the fact that one needs to know WHAT to react to.

You are welcome to think it is ridiculous for needing 5 seconds to process what alert is going off. But the simple reality is no good disaster plan should assume that everyone will immediately understand what is happening.

Well if there are then the world is really screwed.

I wonder if that is enough to help actually. Better that you be holding your phone than a knife or a pot of water when the shaking starts. On the other hand you are startling those people.