Hi Michael. If you will take a look at the 30 day data you can get a better picture as to what is happening in the area.

The data sites where the trace is rising is an indication that the movement is right lateral.

The data sites where the trace is dropping is an indication the movement is left lateral.

Those that are flat indicate that it is locked.

When the fault is locked at a certain point it may not be locked the entire depth of the fault. It may be locked near the surface while still able to move below the locked point, or it could be locked near the bottom of the fault and still move at the surface above the point at which it is locked.

The fault is broken up into segments. These segments are determined by bends or jogs in the fault. Each segment can move independently of another (moderate quake) or move all together (large quake) at the same time. The depth of small earthquakes can at times be an indication of where the fault is locked. Of course the over all depth of the fault at a given location has to be known. If the quakes range from near surface down to about a depth of 20Km it would be fairly safe to say the fault is most likely not locked at that location. If the quakes occur more frequently near the surface then there is the chance the fault could be locked somewhere below, or the reverse could also be true. Then again it could also mean that fault below the point of the quakes is completely free to move, as there are no obstructions.

The best indication I have seen for an earthquake in the Parkfield and SJB areas is the increase in dilational strain. Of course there may not be an indication of dilational strain if the quake of a moderate size was some distance from the data site. I know the 4.1Ml we had a couple of years ago that was 21 miles SSE of SJB just barely indicated an increase in strain.

The biggest problem with the data is seeing enough of it to learn what it is doing and what it is going to do. With each quake I learn a little bit more. Then I have to understand what it is that I have learned. Take Care…Don in creepy town.