In message , Ian Bingham
writes
Your 1st para. - I don't think it happens.

That was more or less my point.

Yours 2nd para. - Why indeed?
An interesting thing about earthquakes: the Ancona quake happened about 0500. There were many after-shocks throughout the day, but you get a
short warning when one is about to happen. Sound waves travel through the earth faster than shock waves, so about 3 seconds (in this case) before
the shock, there is a very low-pitched rumbling sound. When you hear that, you know what's coming.

--
Stewart Robert Hinsley