It has been steadily moving but seismologists say it has only increased the pressure underground.
While predicting earthquakes remains an uncertain science, there has been concern in recent years among experts that the San Andreas fault may be close to a new, major ruction if only by virtue of the length of time since it happened last, when the southern portion of the fault was struck by a 7.9 shaker all the way back in 1857.
Since then the tectonic plates that meet at the fault have been continuously on the move at a rate of about 2 inches per year. That means that over 159 years there has been a shift of 26 feet as the Pacific plate moves in a northwesterly direction against the American continental plate. Every additional inch creates additional pressures on the rocks beneath the earth’s surface that builds and builds until it eventually snaps.”
“California Floods To Trigger “The Big One”? – Geologists Warn Of Quake Risks From Snowpack, Rising Reservoirs”
Now, as the Los Angeles Times points out, the recent flooding in California has prompted some scientists to raise concerns over whether or not Californians are at a greater risk of being struck by an imminent quake.
There are two ways a reservoir can cause an earthquake. A rapid filling or emptying of a lake can change the weight pushing on a fault, which can make an earthquake more likely, said Bill Leith, acting associate director on natural hazards at the USGS.
“Especially for a reservoir as large as Oroville, it’s a huge weight on the crust that’s basically being pulled up and down on an annual cycle. So it wouldn’t be surprising if there were earthquakes associated with that,” Leith said. “The rapid filling, I just think it increases the risk. … I would expect that a rapid rise or a rapid fall in the water level would be much more likely to trigger earthquakes.”
The second way a reservoir can cause an earthquake is from added pressure. Water trickling deep into the earth can increase pressure underground that makes it easier for faults to move, according to seismologist Lucy Jones.”
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