GEOL 111 Earthquakes and

GEOL 111 Earthquakes and

Instructions/Descriptions

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GEOL 111 Earthquakes and

Student Name: ______________________ Date: ______________Grade:

Physical Geology 111 Lab

Earthquakes and Earthquake Hazards

1. Introduction & Purpose:

The purpose of this laboratory exercise is to become successful at applying concepts and techniques of seismology for locating earthquake epicenters, measuring magnitudes, evaluating ground surface stability, measuring active faulting with aerial photography, and assessing seismic hazards.

Part I. Measuring and Analyzing a Virtual Earthquake’s Epicenter Location and Magnitude

1. Part Iis a virtual courseware computer activity that will be accessed online over the Internet at the following website link:

https://www.sciencecourseware.org/VirtualEarthquak…

These online activities are designed to help you learn the concepts and techniques for measuring and analyzing the location of earthquake epicenters and estimating earthquake magnitudes.

Before you begin the program, make sure that your computer system has the proper requirements to run the activities. This interactive online program consists of several components: 1) Images of earthquake destruction; 2) Tutorial; 3) Demonstrations; 4) Travel Time activity; and 5) Epicenter and Magnitude Activity. The online components that will be assessed and graded by me only include the Epicenter & Magnitude activities. However, it is very helpful to check out the demonstrations, tutorials, and travel time activity #4 prior to doing activity #5. You must successfully complete these exercises in order to receive a passing “certificate”. Note that you must save and make a copy out the completion certificate page before you quit the program OR have a copy emailed to yourself.

Again, make sure to save and make a copy of the “certificate” when you finish or have it sent to your email. You will need to upload an image of the certificate with this lab.

1. Locate the distance of an Earthquake

A single earthquake produced the seismograms below at 3 different locations (Alaska, North Carolina, and Hawaii). Times have been standardized to Charlotte, North Carolina to simplify comparison. See if you can use these seismograms and a seismic-wave travel time curve to locate how far the epicenter is from these locations.

1. Estimate to the nearest tenth of a minute in the seismographs above, the times that P-waves and S-waves above first arrived at each seismic station. Then subtract P from S to get the S-minus-P time interval:

2. Using the S-minus-P time intervals above, and the travel time graph below, determine the distance from the epicenter (in kilometers) for each seismic station.
3. Sitka, AK: ______________ km
4. Charlotte, NC: ______________ km
5. Honolulu, HI: _______________ km

Normally you would have to draw circles around each seismic station to determine where their circles intersect, which is the epicenter location for the earthquake. Since we’re online, you don’t have to. Instead, I’m giving you the latitude and longitude location for the Earthquake.

The epicenter is located at 34° N latitude 118° W longitude.

3. Using the map above, what region/state is the earthquake located? What is the name of a major fault that occurs near this epicenter?

Part II. Earthquake Hazards

Why does ground shaking from an earthquake change so much with location?

How seismic waves shake the ground during an earthquake depends on the geologic layering. The figure below shows how an earthquake wave going through solid bedrock has high frequency and low amplitude. When the waves go through weaker material, they oscillate with higher amplitude but lower frequency. Imagine dropping a rock on concrete and recording the vibration compared to dropping a rock on a trampoline or a mattress. Water-saturated sediments are susceptible to liquefaction, which causes sediment to behave like quicksand. Liquefaction typically commonly occurs in regions near bodies of water or where the ground water table is very close to the surface.

1. San Francisco, California is located in a tectonically active region, so it occasionally experiences strong earthquakes. The map below shows the kinds of Earth materials upon which buildings have been constructed in a portion of San Francisco. These materials include hard compact Franciscan Sandstone, uncompacted beach and dune sands, river gravel, and artificial fill. The artificial fill is mostly debris from buildings destroyed in the great 1906 earthquake that reduced large portions of the city to blocks of rubble. Imagine that you have been hired by an insurance company to assess what risk there may be in buying newly constructed apartment buildings located at X, Y, and Z. Your job is to infer whether the risk of property damage during strong earthquakes is low (little or no damage expected) orhigh (damage can be expected).
2. Is the risk at location Low or high? Why?
3. Is the risk at location Yalow or high? Why?
4. Is the risk at location Zlow or high? Why?
5. On October 17, 1989, just as Game 3 of the World Series was about to start in San Francisco, a strong earthquake occurred at Loma Prieto, California, and shook the entire San Francisco Bay area. Seismographs at locations X, Y, and Z (figure above) recorded the shaking, and the resulting seismograms are shown below. Earthquakes are recorded on the seismograms as deviations (vertical zigzags) from a flat, horizontal line. Thus, notice that much more shaking occurred at location Y and Zthan at location X.
6. The Loma Prieto earthquake caused no significant damage at locationX, but there was moderate damage to buildings at location Y and severe damage at location Z. Explain how this damage report compares to your predictions of risk (Part IV. A)
7. The Loma Prieto earthquake shook the entire San Francisco Bay region. Yet, the seismograms show evidence that the earthquake had very different effects on properties located only 600 m apart. Explain how the kind of substrate (uncompacted vs. firm and compacted) on which buildings are constructed influences how much the buildings are shaken and damaged in an earthquake.
8. Imagine that you are a member of the San Francisco City Council. Name two actions that you could proposed to mitigate (decrease the probability of) future earthquake hazards such as the damage that occurred at locations Y andZ in the Loma Prieto earthquake.

Part III – Measuring and Analyzing Displacement on an Active Fault Using Aerial Photography

Part III is designed to familiarize you with how geologists investigate the movement of an active fault by examining aerial photographs and determining the following about the fault: 1) position and extent of the fault, 3) notable offset markers, 4) apparent direction of offset, and 5) amount of offset. Below is an aerial photograph of the San Andreas Fault (a tectonic plate boundary) at Wallace Creek, Carrizo Plain, southern California. Notice the fence line, small streams, and fine features of the landscape. Also notice that the figure shows a portion of the strike-slip San Andreas Fault, which is transform plate boundary separating the Pacific Plate from the North American Plate.

Question 1: How much has the San Andreas Fault offset the present-day channel of Wallace Creek.

Answer: ______________ meters

Question 2: What is the apparent lateral offset movement of Wallace Creek across the San Andreas Fault in this aerial image? Right-lateral or left-lateral?

Answer: ________________________

Question 3: Notice the small dry valley in the lower-left part of the photograph. Infer how this valley may have formed.

Answer: ______________________________________________________________________

Part IV – Earthquake Laboratory Reflection

Directions: Write a reflection of the lab activity, explaining its purpose, the methods used, the results obtained, and a brief personal reflection of what you enjoyed and learned about doing this lab.

1) What was the purpose of this lab? What did you actually discover and learn during this lab?

2) What did you enjoy most about this lab? Also, what was challenging or thought-provoking?

GEOL 111 Earthquakes and

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