Hi David. I plotted the quakes on my map to see how they lined up. This doesn’t appear to be a tight swarm. The swarm covers an area of about 2 miles long and about ½ wide with a north/south trending.

The “first motion mechanism” for the M>2.1 and M>2.2 quakes indicates they are “strike slip with normal-faulting component.” In other words there is some lateral movement with a downward motion. This is known as an “oblique-slip fault.” It is caused by a combination of shearing and tension of compressional forces. They are about 2 to 3 miles east of the Calaveras fault. The Concord fault is in this area, but not sure if it goes that far south. The Pleasanton fault is also in the same area. Take Care…Don in creepy town