Someone might want to look at this no aftershocks after a M5. I suspect, if true at all, that it is just the catalogue...there must have been small aftershocks (M2s at least). The PDEs back then only included "significant quakes" plus those over a certain magnitude. I also don't remember the 7 day warnings, but I suppose I either just did not hear of these or forgot. I do remember a Parkfield warning or two, and know that the Loma Prieta area had been identified (in a paper?) as due for a quake, but did not read that paper so don't know the details.
Chris