1. (2pt) Which type of fault is this? Explain how you found out

2. (2pt) Which type of fault is this? Explain how you found out

Part II – Elastic Rebound

In this section you will watch a short movie and 2 animations demonstrating the Elastic Rebound Theory. Answer the listed questions after each video from what is demonstrates usingthe knowledge you have learned from lectures.

3. Watch the first movie from IRIS Earthquake Science site:

www.youtube.com/watch?v=JYQLIpo4kwk

3.a. (0.5 pt) Describe the movement of the hand pulling the string in the experiment

3.b. (0.5 pt) Describe the movement of the block in the experiment

3.c. (1 pt) When the block is still, what happens to the rubber band?

3.d. (1 pt) When the block is sliding, what happens to the rubber band?

Hint: To answer 3c and 3d, compare the driving force with the friction force.

4. Watch the two animations from IRIS at the following links:

https://www.iris.edu/hq/inclass/animation/elastic_…

https://www.iris.edu/hq/inclass/animation/fault_ri…

Answer the following questions:

4.a. (1pt) In the first animation “Strike-slip with high friction”, deformed rocks store energy, just like the spring in the previous question. What happens to the shape of those deformed rocks when the fault slips during an earthquake?

4.b. (1pt) In the second animation “Strike-slip without friction”, we cannot observe any earthquake. This contrasts with the examples shown above. Explain the role of friction in the formation of earthquakes according to the Elastic Rebound Theory.

Part III – San Andreas Fault slip rate at Wallace Creek

5. Offset Stream Channels at Wallace Creek

The image below is a sketch showing a stream channel (blue) offset by lateral displacement on a fault. The red line shows the surface trace of the fault. The dotted segment shows where the downstream channel was located before displacement occurred on the fault. Points A and B (circles) are called the piercing points, where the downstream and upstream channels intersect the fault, respectively. The distance between A and B is the amount of slip that took place on the fault since the stream was formed.

5.a. (2pts) Is the fault represented in the figure a right-lateral fault or a left-lateral fault? Explain your answer is one sentence.

Open a browser and navigate to the site www.google.com/maps/. In the Search Google Maps box (top-left) enter the location coordinates: N35.272 W119.827 and hit the return key. Display the satellite image by selecting the box “Satellite” on the lower-left side of the window.

The image is centered on the Wallace Creek site on the San Andreas fault (similar to the figure below). Wallace Creek was named after Dr. Robert Wallace from the US Geological Survey, who studied “paleoseismology” by searching evidence of past earthquakes on active faults. It is at Wallace Creek that the long-term slip velocity of the San Andreas Fault was measured for the first time (http://activetectonics.asu.edu/ActiveFaultingSemin…). (Hint: in the Google Map view, the San Andreas Fault trace is a line from the top-left to the bottom-right of the image).

Observe the image and find the active stream channel that Bob Wallace used to estimate the fault displacement. Locate the piercing points A and B as defined above on the image and measure the distance along the fault between them as follows: Control-click (or right-click) on Point A and select measure distance in the menu, then click once on Point B. The distance is shown in feet on the map and in meters in the box at the bottom.

5.b. (2 pts) How much displacement did the Wallace Creek recorded since its incision? Give the result in meters.

5.c. (2 pts) We know from the analysis of 14C samples from sediments that the stream channel was incised 3,800 years ago. What is the average slip rate on the fault since the incision of the stream channel? Give the result in centimeters per year.

5.d. (2 pts) If an earthquake typically shifts the ground by 6 meters, how many earthquakes contributed to the offset stream? Round the number to the nearest integer.

5.e. (2 pts) In this scenario, what would be the average recurrence time (in years) between earthquakes along this section of the fault?