Keep on keepin' on

Since we were talking about the San Andreas Fault earlier this week, I decided to make it easy on myself and stick with the same topic for today’s lesson. There’s so much wonderfulness to discuss when it comes to this, our most favoritest fault.

The San Andreas Fault is the reason behind all sorts of landforms we see across California. Let’s start by looking at a map of this guy:

Ahh, the lovely California. What should stand out to you when you look at this map are the mountains that follow along the red line (the trace of the San Andreas Fault). The presence of these mountains makes sense seeing as all this movement along the fault mooshes the Earth's crust together in and around the fault zone. The whole Basin and Range province in the western part of North America is an after-effect of the Pacific/North American plate boundary, but we’ll leave that discussion for another day. Totally different topic.

Anywho, start with your eyes on the northern most part of the red line and then trace the red line southwards, towards Los Angeles. You’ll get to a point just south of the Great Valley (the Armpit of California) where you’ll see that the fault curves a bit inland. This curve is called “The Big Bend” and causes all sorts of interesting things to happen, geologically speaking.

For one, the Big Bend is responsible for the uplift of the Transverse Ranges.

This range of mountains is an oddball because it runs East-West, while everything else around us (the Coast Ranges, the Sierra Nevadas, the Rockies, the Cascades) runs North-South. Why you ask? Well, think of the Pacific plate moving northward and rubbin’ up against the North American plate. It’s cruisin’ along, carrying with it all those rocks and houses and dogs and buildings and burrito shops that exist west of the San Andreas. At the Big Bend, however, all that stuff is crashing into one another instead of smoothly moving along past one another. That seemingly innocuous curve in the fault has created a big, fat convergent zone in the area around the Big Bend. This convergent zone includes the Los Angeles region. Lucky us!
Along with the Transverse Ranges, we get the Garlock Fault out of all this Big Bend business. The Garlock is one of the larger lateral faults in California. If you’re ever flying north from Southern California, you can actually tell where this fault runs visually if you look out your airplane window. Pretty neat, huh? Make sure to point it out to the person sleeping next to you by saying “Hey, look look! That’s the Garlock fault! It’s a left-lateral strike slip fault that defines the boundary between the Mojave block and the Sierra Nevada/Basin and Range province!” I advise to also make sure to spit a lot when you talk and maybe sneeze on them once or twice because you are a nerd and should behave thusly.

NEEEERRRRDDDD!

Food and Faults

Alright everybody. Let’s shake off the cobwebs and get back learnin’, shall we? Today we’ll talk about a place that we all know and most of us love: California. Specifically, we’re gonna look at how the San Andreas Fault was born. It’s kind of a weird story, but an important one to know for the sake of understanding why California looks the way it does. And there will also be a food analogy, so read on!

Remember back when we talked about plate boundaries? The places where those big tectonic plates crash into and move along with one another? No. Well, let’s remind ourselves before we move on.

There are three types of plate boundaries: divergent (pulling apart), convergent (crashing together) and conservative (rubbin’ against one another). An example of a divergent plate boundary is the East African Rift, of a convergent boundary we’ve got the Himalayas, and for our conservative boundary we’ve got the good ole’ San Andreas Fault.

For most of the last 600 million years, the western part of North America was a convergent plate boundary. An old old plate that doesn’t exist anymore called the Farallon plate was happily subducting underneath North America (see Figure). What happened was that there was a pointy bit of the Pacific/Farallon plate boundary that rammed into the North American subduction zone about 30 million years ago and everything went apeshit. When that pointy bit hit North America, the subduction zone along the western margin started swallowing up a divergent zone (where new crust is being made). Instead of one outdoing the other, the whole thing just fell into a new regime altogether and we got a conservative plate boundary. Why, you ask? I don't think we have a good explination as to why we got the San Andreas out of this mess. Or at least I don’t know anybody that knows why. It’s like taking a hot dog and smashing it together with a hamburger and ending up with sushi. Crazy!
The sushi that we ended up with is the San Andreas, the big mother of all faults in California. Unless you’ve been living in a cave or on the East Coast or are totally oblivious to all that surrounds you, you probably know that this is the fault that gives everybody the jitters. And rightly so, it’s a big fuckin’ fault that has caused a lot of problems in the past. The San Andreas Fault serves as the boundary for the North American plate to the East (what the rest of America is attached to) and the Pacific plate to the West. Yes, that means in a few million years Los Angeles will be sittin’ pretty right next to San Francisco. Don’t frown, San Francisco. Surely by then we will have engaged Iran in nuclear conflict so you won’t have to put up with anything more than the mutated remains of model/actress zombies looking for temp jobs.

Zing! It’s good to be back!

I know, I KNOW!

Sorry I have been lame and not posted about science in a while. Shit has been busy for your favorite Geochemist latley. Vacation, divorce, vacation, walking dogs, vacation, spreadsheets, vacation, cartoons, and cheese! You know how it goes. Looky here: I'm heading back to the office on Monday and will start up writing you more science things, ok? My little heart swells with happiness that my friends love learning about the boring shit I work on. Thank you for your patience, I assure you that it WILL be rewarded.

In the meantime, head on over to www.chiefmag.com for a fancy article about zombies and physics written by yours truely.

Love,
Tabitha and Paris Killton