Hi All. I’ve done a lot of digging (and not with a shovel) to see what I could find in the way of data for the Calaveras fault in the area of San Ramon. What I learned was interesting, but not much else.

In the San Ramon area, the fault is typified by a series of parallel offsets and stepovers, with very little reliable information as to which of the breaks is the "active" trace that is thought to have broken the ground surface in 1861. In the late 1970;s, Rowland (1977, 1979) undertook a particularly interesting study of the fault in south San Ramon for the Twin Creeks portion of the old Bishop Ranch. In the second study (Rowland, 1979), a large trench was excavated with scrappers, down to a depth of 20 feet.

Much remains to be revealed about the true character and extent of the San Ramon segment of the Calaveras fault. Ancient landslides and other surface deposits hide approximately two-thirds of its supposed surface trace. In addition, the fault zone itself is extremely complex, containing a multitude of splays, step-overs, and other structural discontinuities. Despite reports of what must have been a M. 5.6-6.9 earthquake on July 3, 1861 no collaborating surface trace of sufficient consistency has been identified to date. In fact, with the exception of the area south of Castlewood and that in Dublin, the fault yields little insight as to which of its many traces are the most active. Surface creep features that are common on the Hayward, Rodgers Creek and Concord faults, appears to be absent along the San Ramon segment of the Calaveras fault.

The Pleasanton fault is about 5 miles to the east of the Calaveras fault. When I started plotting the quakes on the map I first thought the quakes might be associated with this fault. However that doesn’t appear to be the case as the quakes are east/west trending with the greatest concentration a little more then a mile east of the Calaveras fault. That is if the Calaveras fault is located correctly.

The “first motion mechanism” is showing everything from strike slip to strike slip with thrust faulting component, to strike slip on a down dipping fault to strike slip with normal faulting component. I don’t know if it’s possible for a single fault to have this many variations of quakes in such a small area. This leaves the possibility of more then one fault being involved with this series of quakes.

The quakes in 1970 appear to have occurred a little further to the north and were also a little further to the east then the current swarm. Some of them are as far south as the northern most quakes in the current swarm with a couple of them inside the current swarm. Can’t rule out the possibility that the current swarm is taking up where the 1970 swarm left off. What this holds for the future is anyone’s guess. For right now I’m just going to sit back, put my heels up and wait and see as to what ever happens, what ever and when ever that might be. Take Care…Don in creepy town