LA has an earthquake warning system. Did it work during July 4th’s 6.4 magnitude event?

Los Angeles will lower the level at which earthquake warnings get sent to residents, city officials said after a 6.4 magnitude quake on Thursday morning, July 4, failed to trigger an alert.
The early warning system did work, U.S. Geological Survey seismologist Robert Graves said during a televised news conference, in that it detected the temblor before it happened. But the ShakeAlert app wasn’t set off – it would have sent alerts to people’s cellphones – because it’