Visualizing the birth of the San Andreas

Tanya Atwater (who figured out the San Andreas Fault back in the day) was just here, speaking to our local geological society and talking to classes. She's been working a lot on making animations to help people understand geology, and I wanted to share a couple that she showed to my structure class.

These are Quicktime movies that can be either viewed on Tanya's site or downloaded.

Here's the Pacific Ocean from 80 million years ago to present, and here is western North America from 38 million years ago until now. The first movie shows three big plates in the Pacific Ocean: the long-lost Kula plate, the Farallon plate (which is mostly gone, too, except for that little piece now known at the Juan de Fuca plate), and the Pacific plate. You can see the Kula and Farallon plates get smaller and smaller, until the Pacific plate touches North America... and somehow the plate motions were almost right for a strike-slip plate boundary. The second one is a close-up of North America, and you can watch the San Andreas form and grow through time. (You can also see some of the other big changes in western North America, especially the stretching of Nevada to double its original width.)

If you've been told about the story of the San Andreas Fault, but weren't able to picture it, check it out. My students loved these (and the professionals at the meeting did, too).