Hi All. I have talked about the Great Valley thrust fault in the past mostly because there wasn’t that much attention being given to it. However recent events gives me cause to say that maybe it’s time someone paid a little more attention as to what is taking place along the fault at present time. It’s not anything that jumps out at you, but more like a gentle tap on the shoulder.

The 1983 Coalinga 6.5Md was associated with the Great Valley fault. The Vacaville 1892 6.5M and the Winters 1892 6.2M quakes are associated with the Great Valley fault. Incidentally these two quakes occurred on April 19 and 21.

The more recent events are the Los Banos 3.0Md on 02/15/01 is most likely associated with the fault.

Today’s Avenal 2.2Md 02/20/01 is associated with the fault.

Today’s Yountville 2.1Md 02/20/01 event may be associated with the fault, but more likely it’s associated with the Green Valley fault. In the past two years there has been a slight increase in activity (or maybe I’m watching it a little more then usual) along the entire length of the fault.

The Great Valley ophiolite is a complete ophiolite section along the entire 600 km length of the Great Valley. In the northern Great Valley it includes an unserpentinized mantle section, whereas in the southern Great Valley the mantle section, if present, is serpentinized to such a degree that it cannot be distinguished from Sierran basement, or ophiolite crust on the basis of velocity and density. The ophiolite may have penetrated further east beneath the Great Valley in the north than in the south. Wedging of Franciscan material appears to have truncated the western margin of the ophiolite at mid- to lower-crustal depths in the north, and to have been confined to upper-crustal depths in the south, allowing the ophiolite to extend west beyond the western margin of the Great Valley at mid-crustal depths in the southern Great Valley.

As you can see from the description off the fault there is the potential for a major quake (depending where it centers at) to occur. The over all quake history of the fault is not well known. At least not on the web.

I would appreciate any information or feedback that anyone may have concerning this fault. Take Care…Don in creepy town.