Hi All. The latest swarm in the San Ramon/Dublin area appears to be a continuation of the swarm in Nov. 2002. Today’s 4.2Ml is the strongest quake to have centered with in a 25-mile radius of it. This was in 04/28/2002 and was an M>4.3. The strongest quake to have centered within a 25 mile radius of today’s quake was an M>5.7 in 03/31/1980.

Both the “first motion mechanism” and the “moment tensor solution” show the quakes to be almost a pure strike slip. This type of motion would be compatible with the Calaveras fault however the same kind of motion was seen with some of the quakes in last years swarm.

Not knowing for sure which way the fault dips in this area, or that it even dips at all it’s hard to say that this latest swarm is associated with the Calaveras fault. A depth of 10 miles could indicate they are occurring on the Calaveras fault if the fault dipped to the SE.

One report had the M>4.2 quake being felt in Petaluma. I don’t see any unusual aftershock pattern in that area, so most likely Petra never felt it. Sorry about that, but I just couldn’t resist saying that. Take Care…Don in creepy town