Saturday, May 21, 2016

The San Andreas Fault

As everyone knows, southern California is going to fall into the Pacific Ocean any day now so we thought it would be timely to report on the cause of it all.  The San Andreas Fault is the eight hundred mile long tectonic "seam" between the Pacific and North American plates.  That seam is actually quite sizable beyond its length.  At its widest it is one mile across; at its deepest it's ten miles down.  We'll have to trust the geologists on this since the only markers above ground are bodies of water that line up perfectly over the fault and some mountain ranges which we'll get into later.

The eight hundred mile length extends from the gulf of California, which separates the Baja Peninsula from mainland Mexico, to offshore northern California.  If it were a straight line it would exit the state just south of San Francisco.  As it is, it has a couple crooks in it but otherwise it is remarkably straight.

Technically the San Andreas is a "transform" fault which means the two plates are side by side or horizontal to each other as opposed to a subduction fault which involves one plate going over another.  That is the more destructive type.  In the San Andreas case, the Pacific plate is moving north (and west) at a clip of two inches a year.  The North American plate is also moving north but much slower so the seismic rubbing of the two against each other is almost continuous and, for all intensive purposes, eternal.  Geologists have figured that the total movement of the plates has resulted in a three hundred fifty mile change in terrain which means this has been going on fifteen to twenty million years!

So the normal rubbing results in the "creeping" northward of the Pacific plate but that creeping is more in the way of fits and starts as opposed to smooth sailing.  Some of those seismic "fits" just barely register on the graph while others like the 1906 and 1989 San Francisco quakes resulted in disaster.  As for southern California, 1857 was the last time they were hit with a quake so they're w-a-a-y overdue. The 1994 Northridge quake we remember was related to a different fault.

So why are we interested in this now?  Because we just got in the 2013 Firestone Vineyards Cabernet Sauvignon from the Santa Ynez Valley which exists as a direct result of San Andreas seismic activity.  That valley is a lengthy east-west valley in southern Santa Barbara county.  The north-south mountain ranges separating the Central Valley from the coast make perfect sense as a result of the San Andreas fault.  It's like when two people in bed rub up against each other creating a ridge in the quilt over them.  The east-west valley, however, also makes sense if either or both individuals kick the covers toward the foot of the bed.  The fits and starts of seismic activity create valleys like that too.

Firestone Vineyards also benefits from being located over the Pacific plate west of the fault.  The North American plate geology to the east in southern California is uninteresting, to say the least.  The Pacific plate features an easy draining shallow ancient marine sediment like much of Europe.  On top of that, the valley opens up to the ocean providing a trough of cool breezes making Santa Ynez Valley cooler than most of the state.  Firestone is one of a hundred wineries taking advantage of these optimal conditions in Santa Ynez Valley.

No comments:

Post a Comment