Hi John. A seismologist told me that she thinks the main reason we see more quake swarms in Southern California is that the crust is thinner there.

The swarms in Northern California seem to be confined to certain areas such as Dublin, San Ramon and Alamo. In Dec. of 1981 there was a 22-quake swarm within a 1Km radius along the Rodgers Creek Fault just east of Petaluma. Nothing ever came of that either. I talked to a couple of seismologist about that swarm and the only thing they could come up with is that it could be a weak spot. There were 3 quakes at M>3.0+ with a depth of 7 to 9Km. There were 4 quakes at M>2.0+ with a depth of 4 to 6 Km. The rest had a depth of 0.03 to 2.7Km. All of the magnitudes are listed as Md.

When I opened the search to 8Km and started with the year 1898 the count went up considerably with the greatest majority of the quakes occurring northeast of my center quake (38.3008/-122.6105) There are very few quakes occurring south, or west of this location. I’m not 100% sure about this but I believe this swarm is west of the Rodgers Creek Fault. There are rolling hills in the area with most of them looking like a slide waiting to happen.

Things like this fascinate me. Always have. There is a message there if we could understand it. My job and training as an analyst for the Air Force also made me just that more inquisitive. Take Care…Don in creepy town