Hi Chris. There are two theories as to why the Parkfield quake hasn’t occurred yet.

The first is that the 1983 Coalinga quake was the Parkfield quake. The epicenter of the quake was about 18 miles east of Parkfield and is thought to have been caused by the Great Valley Thrust Fault.

The second theory is that the Coalinga quake reduced the stress in the Parkfield area making it less likely for a large quake to occur anytime in the near future.

From what I have been able to learn is that the San Simeon quake increased shear on the San Andreas Fault in the Parkfield area. When I checked the crustal deformation sites at Parkfield and San Juan Bautista an increase in creep could be seen at both locations. However in as much as creep is measured at the surface this may only be surface movement due to the seismic waves moving through the area.

Checking the ANSS quake catalog with a 10 mile radius I found that there was a slight increase in quake activity in the area of Middle Mountain in the last 10 days of October. This slight increase in quake activity continued through the months of November and December up to the time of the San Simeon quake at which time the number of quakes decreased slightly. The quakes in January appear to be close to what has been seen in the past. There could be a connection between this activity and the San Simeon quake, but one would be hard pushed to make a case for it.

Now for the $64.00 question. Was the San Simeon quake the Parkfield quake only this time it was in the other direction? It has been just a little more then 20 years since the Coalinga quake. Sorry. The Devil made me do it. Take Care…Don the little Devil in creepy town