Those suck. Copper, steel, or pex?

Pex.

I thought the cause was the quake but it seems from the mold I found when moving the vanity that the spray had been going for some time already.

The leak has been fixed with a shark bite connector.

Those pinhole leaks are fun aren't they? Had a similar thing happen (minus the earthquake) when I was on holidays some years ago. Pulling up in front of my house upon my return I briefly wondered why every window in the house was fogged up on the inside before a sinking feeling of dread took hold. Copper water line to the humidifier on the furnace had developed developed a pinhole and was spraying out straight into the basement. Made me twitch a bit cleaning up that mess. Twitched a little more when the water bill showed up.

Hope you got all the mold! That stuff can do a number on your lungs.