This may be nothing, or it might be something. This posting is similar to an earlier one I did about the fault systems near me. What’s different this time is the activity has moved.
All I can say for certain is that I’ve been watching the California fault system for a long time (since a Geology class in about 1974) waiting to see this.
Now it’s here.
The problem is that I’ve not watched continuously and closely the whole time, so it might have happened before and I just missed it. This might not be as unique as it seems.
What is it?
The earthquake energy has shifted onto the Hayward / Calaveras system and off of the San Andreas north of San Juan Bautista (near Hollister). Notice how the line of quakes moves off of that red line that passes under San Francisco. That big red line is the San Andreas Fault.
Quakes in California 29 December 2010
We have huge continuous activity down in Baja and over into Southern California, then it splits and heads north. Some up the mountain path, and a lot up the San Andreas. ( I note there are two ‘dinky’ quakes near Mount Shasta and Mount Lassen, our two most active volcanoes, but they are only 1.x scale. Odd, though, that we get one near each of them up there near Redding on this California map).
Why does this matter?
There is a long standing pattern in the geologic record that the San Andreas has a Great Quake, then the more inland Hayward / Calaveras system has a great quake “some years” later. Exactly how many can vary a bit.
We had the Loma Prieta quake on the San Andreas, though in some ways it was only a ‘half a quake’ as only the part more southernly than about Santa Cruz “let loose”. The part under San Francisco and out to sea stayed locked. (Though you can make the case that the 1906 Quake released the top half, so this ‘bottom half’ was the laggard bit and has now ‘caught up’).
The reasonable expectation is that the next “Bay Area Great Quake” ought to happen on the Hayward / Calaveras side of the bay. One of those faults runs right under U.C. Berkeley…
The reasonable expectation would also be that the faults would start showing some ‘pre-shock’ activity prior to the Great Quake. So I’ve been watching these faults since the 1970s when my “roomie” swapped to Berkeley to get his business degree and the parties moved to ‘his place’. I’ve watched, and waited. Seen the San Andreas get angry and seen nearly nothing on the East Bay side.
Now this pictures shows the San Andreas most quiet north of where the Calaveras splits off. That “hot spot” on the north side of the bay / delta in the upper left corner is near The Geysers volcanic hot springs area. Hmmm… that volcanic thing again…
All the action is now more inland. Something has changed. And there is a fair amount of action too. Yes, all of it small. But big trees from little acorns grow…
Quakes in the East Bay / Berkeley Hills 29 Dec 2010
Here you can see how the activity is moving up the San Andreas until it reaches Hollister (near Mission San Juan Bautista) then it transitions onto the more inland fault systems.
Quakes near San Juan Bautista / Hollister 29 December 2010
There has been a ‘regime change’. The activity is moved. Something is different.
What to make of this? I’m not sure. The entire interior of North America is showing more activity. There is a spur running into the Sierra Nevada Mountains and some spreading up toward Yellowstone. It’s as though the ‘slip’ action along the San Andreas is slowed / stopped and a more compressive action is moved into the mountain building parts of the West. The parts with volcanoes.
OK, so take a look at this USA map. Notice how there are “lines” of quakes running up the mountain chains? Yeah, they are active mountain building regions. Yeah, they are supposed to get quakes and have lift. But… we’ve not seen that MUCH action in prior years. I know, a human lifetime is barely an eyeblink to these things. I’m watching on the wrong “time scale”. But still, that pattern. Up the mountain ranges. It’s different. And different is interesting… Even Washington State and Oregon are showing activity in the mountain parts; away from those offshore fault lines.
Earthquakes in the USA 29 December 2010
In Conclusion
At this point I think it’s pretty much a “done deal” that Berkeley / Oakland get the next “great quake” in the San Francisco bay area. The only question is when. Given this change of activity pattern, I think that answer is soon on a geologic time scale. The problem is that “soon” could still be a couple of decades away.
If I had to bet money on it?
I’d give it 5 years or less.
If I had to bet a whiskey on it?
I’d give it 2 years.
OK, I’m near that San Jose spot on that East Bay / Berkeley map. About as far from the San Andreas as you can get before you start getting closer to the Hayward / Calaveras. (The two names come together as they start from about the same place, where they split from each other is near Fremont. The Hayward goes under the city of Hayward, then Oakland and Berkeley. The Calaveras goes on the east side of the hills and near the Calaveras reservoir / lake. They tend to share activity between them.)
So I’m unlikely to have much impact from a quake on that system. Still, it ‘bears watching’ for me, as a great quake there will likely mean I need to run the generator and live on stored food and water for a few days. It’s a reminder to me to check the stored supplies and make sure glass things are not on the fireplace mantle… In exchange for having only “half a quake” from being further from the fault, I get one twice as often as I’m “near enough” to both of them. I’ll take twice as often at far less power each…
The nice thing is that this can be a small fixation, watching the faults; but as it won’t really hurt me where I’m positioned, it’s rather like watching somebody ELSE fight at the football game, just two rows away… You get all the excitement, but none of the black and blue bits ;-)
At any rate, I hope you find the patterns on these charts as interesting as I do. They are quite different from what we saw even just a year ago. Many more ‘minor quake’ spots, and much more inland. Something is afoot… it’s just not clear what.
Musings from the Chiefio 
Excellent piece and very scary if you are on the Pacific plate in California as it will all move at once in the manner it did in 1857 when it shifted as much as 20 feet in an instant at some locations.
Earthquake insurance is still cheap and a very good investment, if you can get it.
One thing I noticed a couple of years ago was the appearance of the quake activity along the Eastern Sierra. I couldn’t be sure if this was new activity or if it was due to an improvement in the monitoring network there but it seemed to appear one here, one there, and has kept up to the point where it seems there are always quakes shown on the Eastern Sierra.
Another thing to note is the formation of a new fault (White Wolf Fault) North of the Garlock fault zone. It runs from about Bakersfield over to China Lake and some have speculated that it is replacing the Garlock.
I have also been watching the activity on the Coyote Creek/San Jacinto zone. It has been a long time since the Southern end of the San Andreas slipped (say South of San Bernardino). The zone of the Ft. Tejon quake is due for a repeat performance, too.
It seems I read someplace that the San Andreas generally has a large quake somewhere along its length about every 100 years. 1906 was the last one. We are due.
Also, since the quake in Santa Cruz, things have been unusually quiet along the San Andreas North of about Gilroy. A little activity there would be a return to more “normal” quake activity.
Talk about inland quakes, there was a 3.8 quake felt in Indiana and Ohio today (12/30/10 for those not looking at the stamp).
But you weren’t talking that far inland, were you?