Lesson 14: San Andreas Fault System

Crystal Reservoir--SAF (photo by M. Miller)This week we'll explore what is, without a doubt, one of California's best known geologic features: the San Andreas fault. During the past 28 million years this strike-slip fault system has grown to a length of 1,350 kilometers and now stretches from Cape Mendocino to the Gulf of California. It is the principal boundary between the North American and Pacific plates, and differs markedly in structure and earthquake potential (see Fig. 13-22) along its length . Some segments are marked by narrow valleys (as at Crystal Reservoir, right) whereas others are broad zones in which slip is distributed across several parallel strands. Despite these differences, however, we'll see that much of the fault's behavior can be understood in terms of how a particular segment is oriented relative to the direction of plate motion.

In chapter 14 Harden begins with a brief overview of the tectonic setting, age, average slip rate and topographic expression of the whole San Andreas fault system. Then she describes the geologic features that characterize each of the fault's six major segments (and the closely-related Garlock fault and Eastern California Shear Zone) and recounts the major historic earthquakes that have occurred along each segment. As you study the San Andreas I would like you to focus on "big picture" concepts—such as, "Why is the Big Bend segment of the fault associated with thrust faults beneath the LA Basin whereas the Salton Trough segment is associated with crustal extension?—rather than the names and dates of individual earthquakes. Finally, this week's exercise asks you to read and write an outline of one of the articles I've chosen for you about California's geologic hazards or resources.

As you read about the San Andreas fault be sure to take careful notes on the topics covered by the learning objectives below. As during previous weeks, you'll find that writing out key facts in your own words or making neatly labeled drawings will help you better understand the significance of what you've read and spot any gaps in your knowledge. Don't hesitate to post any questions you have to the Discussion Board so that your classmates or I can help you figure them out. Having good notes will also make it easier for you to review for this week's quiz and and access what you've learned when you want to refer back to it for future assignments. Be sure that you are prepared to meet the learning objectives outlined below before you move on to the quiz at the bottom of the page.

Weekly Learning Objectives

Upon successful completion of this week's lesson, a student is expected to be able to:

Reading and Browsing Assignment

Exercise 14: Outline of Article 2 (Due by 9:00 AM on 25-Apr-2011)

This week's exercise is to complete the third of our four writing assignments. To learn about the assignment read through the pointers below and then click on the "Resources" link on the left side of this page, scroll down, and click on "Outline 2" under "Writing Assignment" near the bottom of the page. This week we'll be completing steps one and two and you'll be turning in the outline of the article you choose from the second set.

Quiz 14: San Andreas fault (Due by 9:00 AM on 25-Apr-2011.)

After you feel you have met the learning outcomes outlined above please complete Quiz 14 in the Etudes "Assignments, Tests, and Surveys" tool. There are ten questions about the San Andreas fault and each is worth one point. If you can answer all of them correctly it means that you know your way around the San Andreas pretty well and are ready to start learning about California's coast and the processes that operate there next week. Like all of our weekly quizzes, this one is timed (you'll have 30 minutes) and must be completed in one "sitting". (That is, you will only be granted access once.) So, be sure you're ready to complete your quiz when you start it—and be sure you're using Firefox. Good luck.