Don...various people, including Lowell W. and me, noticed a large swarm of earthquakes in Santa Monica Bay about a week before Northridge...I think it may have had quakes over M4....there was some science discussion by others that there may have been some relation....Lowell and I discussed this swarm by email before Northridge. I think Lowell claimed to have predicted Northridge in sopme fashion but I don't know if I saw that prediction..and am pretty sure I did not see it before the fact...
Your map does not include these quakes...I suppose because they were outside your search radius..
Chris