There are apparently quite a few observable earthquake precursors. Cracks in building foundations are just one. And I am not proposing that they are reliable. The point is that if you are a government official and someone contacts you and tells you that you could be about to have a destructive earthquake then you will probably want to look around for some confirmation evidence. That is what I often tell people to do. And if around the same time that the warning arrived large numbers of people began to notice that there were fresh cracks in their building foundations then that could provide some confirmation evidence.

In developing nations the confirmation evidence has to be fairly easy to observe. People living in areas where houses are made of brick and mud obviously cannot monitor radon gas emissions. They need something simple to work with.