Activity II: Southern California
The following map shows the position of the San Andreas Fault (SAF). There is a plate boundary between the North American Plate (east side) and the Pacific Plate (west side).
The legend shows different types and ages of rocks where the older rocks are shown at the bottom of the legend in green (Cretaceous). Yellow (Quaternary) are the youngest rocks on this map. The colored bodies of rock used to match each other on either side of the fault. (11.5 pt)
What type of plate boundary is the San Andreas Fault? You can use your textbook for help. (0.5 pt)
2. Calculate the rate of movement of the fault by measuring the Oligocene volcanic rocks (orange) in cm/yr. (Ma = m.y. = millions of years) The fault became active 20 million years ago. Your distance measured will be in the numerator and 20 m.y. in the denominator. Rate = distance divided by time. SHOW YOUR MATH. (2 pt)
Step 1: Lay a piece of scratch paper on the map below so that the edge of the paper is along the fault.
Step 2: Put a tick mark at the start (left side) of each of the Ov orange blobs.
Step 3: Bring your scratch paper to the scale at the bottom of the map. Determine the distance in kilometers.
Step 4: Divide your distance by 20 m.y. (Hint: your answer will be a two-digit number in km/m.y.)
Step 5: Convert to cm/yr. To do this, first multiply your answer in Step 4 by 100,000 cm/km and divide by 1,000,000 yr/m.y. In your conversion math, both km and m.y. will “cancel out” and you’ll be left with cm/yr. Please show all math.
3. Now calculate the rate of fault movement in cm/yr for the Oligocene sedimentary rocks (brown) with the same five steps you used in the previous question. SHOW YOUR MATH. (2 pt)
4. What is the average rate in cm/yr? PLEASE SHOW YOUR MATH. (1.5 pt)
Step 1: First add #6 and #7 answer.
Step 2: Then, divide by 2. Be sure to include units of cm/yr.
5. If an offset body of rock was only 10 million years old (the fault became active 20 million years ago and continues through present time), how would its mapped displacement (amount of offset) differ from that of the Oligocene rocks? (Answer in general. This is not a math problem.) (1 pt)
6. What is/are the hazards associated with this type of plate boundary? (1 pt)
7. Did you know Los Angeles and San Francisco will eventually be neighbors? How long will this take? Calculate how long it will take for Los Angeles to meet San Francisco. Time = distance divided by rate. SHOW YOUR MATH. (2 pt)
Step 1: Use a piece of scratch paper and measure the distance in kilometers between Los Angeles and San Francisco. (Do not use the Internet).
Step 2: Convert your measured distance from km to cm. Multiply by 100,000 cm/km. You’ll have a very large number in cm.
Step 2: Now divide the distance in cm by the rate you calculated in number 8. The units of centimeters will “cancel out” and you’ll just be left with years.
Explain why the popular notion of “California falling off into the ocean” is a myth (impossible). Include what will happen along the San Andreas Fault. Avoid use of the word “it” in your answer. Please use full sentences. (1.5 pt)