Hello again!
I’m back in the United States in sunny California! This time I went to see the San Andreas Fault, a 810-mile-continental transform fault that runs through California. The coordinates are N 39° 0′ 14″,W 123° 41′ 48.0001″.
This morning I awoke to the beeping of my phone. The clock read 7:30. I was staying at the splendid hotel named Hotel Hilton Molino Stucky Venice. The sun was already there to greet me through the translucent curtains. I change into traveling clothes and pack a snack, sunblock, and my camera into my day pack before going down to breakfast. After 30 minutes, the tour bus came to the hotel and I was on my way to the one of the world’s most famous transform faults!
After about 2 hours on the road, we came to the Carrizo Plain in southeastern San Luis Obispo County. This is one of the best places to see the surface fractures of the San Andreas Fault. Look at these pictures I took from a high point in the park! Pretty scary huh?
After letting us wander around the park for a while, the tour guide called together the group of about 20 people and started explaining about the Fault. This is what I learned:
Two plates, the Pacific Plate in the west and the North American Plate in the east relatively, meet in western California and are sliding past each other. The rate of this sliding is approximately 33 to 37 mm per year across California, but this doesn’t mean that it is constant. The sliding happens intermittently and somewhat irregularly. This Fault has only existed for about 5 million years.
The Fault was formed in the lithosphere, composed of the crust and the solid rocky portion of the upper mantle. As the two plates continue to slide past one another, the rubbing causes stress and causes the surface to form fractures or faults.
As I looked around, I noticed the lack of volcanoes. This, as I have previously learned from the Himalayas, is because neither plate is subducting under the other. They are just sliding past each other. So there is no magma or any way for the magma to rise up. Thus explaining the absence of volcanoes.
Earthquakes in California are most likely caused by the San Andreas Fault. The plates are not very slippery but rocky and sometimes get stuck when sliding past each other. This builds tension and earthquakes happen in order for the tension to be released. There is also a large bend in the fault which makes it difficult to slide past each other.
Scientists have made studies that show that the San Andreas Fault breaks in relatively infrequent, yet big earthquakes. The last big earthquake had as high a magnitude of 8.25 in 1906. Since then, there has not been as big of an earthquake as the San Francisco earthquake but it is believed that the next big earthquake will be in 50 some years. The last earthquake was in 2011. This earthquake, called the 2011 Cox Sleeper Earthquake, was a magnitude of 4.5. Fortunately, there were no or few reports of damage.
Images: http://thulescientific.com/
http://sciencedude.ocregister.com/tag/san-andreas-fault/
Ashley's Tectonics Tour 