Hi Steve. There is some good logic in the method USGS is using, but I have to wonder just how good it really is.

The Hector Mine quake had 10 foreshocks none of which was greater then M>3.7. This was in a radius of less then 2Km.

The Landers quake had 24 foreshocks none of which were larger then M>3.6. This is with a radius of less then 1Km.

The Northridge quake had no foreshocks. At least nothing that stood out.

So here we have 3 quakes with close to the same magnitudes. Two were preceded by a vigorous foreshock activity while the other snuck in. It seems to me that while based on just two quakes a vigorous swarm of quakes such as the ones that preceded the Landers and Hector Mine quakes may/should also be looked at in terms of issuing a warning. My speculation is that they are. Of course you can’t issue a warning every time there is a swarm of quakes, but it sure wouldn’t hurt to make people aware of it. Take Care…Don in creepy town