Hi All. The swarm in the Livermore area is kind of interesting in that unlike past swarms in the immediate area there are more M>3.0+ quakes occurring then in past swarms.

Using a 5-mile radius there have been swarms in this area in 1943, 1970, 1972, 1977, 1980, 1983, 1989, 1991 and 2002.

In the case of the 1943 swarms there were two M>4.0+ quakes. The swarm was a small one, but this may be due to the lack of seismographs in the area. There was an M>4.0 quake in 1969, but no swarm.

The 03/31/1986 M>5.7 quake occurred 18 miles south of the current swarm. There was a swarm associated with the quake. The swarm occurred on 03/24/1986. There does appear to have been an increase in the number of quakes in that area starting around 1980. However I really don’t think there was anything there that would give an indication that there was going to be moderate quake anytime in the future.

The other thing that makes this current swarm interesting is that like the San Ramon swarm sometime ago there are some “pure thrust” quakes being indicated as well as some strike-slip quakes with thrust fault components. My fault map shows a fault in the area, but isn’t named. It is identified as a late Quaternary fault (about 1.6 million years to present time) with movement during that time.

On January 24, 1980, an earthquake of M>5.5 occurred approximately 12 kilometers southeast of Mount Diablo and was followed within two minutes by after-shocks of M 5.2 and M 4.2. This quake appears to have occurred on, or near the Greenville Fault. There doesn’t appear to have been any swarms, or quakes that could have been foreshocks to the quake.

So here we are. We have had two moderate quakes with no readily identifiable swarms or foreshocks and swarms with no moderate, or large quakes following them. At least none that would indicate that to me. Things like this still bother me though. This movement although small could be making just enough room for a nearby fault such as the Calaveras Fault to move. That is if the Calaveras Fault is being prevented from moving because it is to tight to move. Take Care…Don in creepy town