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# When Nature Strikes: Earthquake Model Investigation

 Summary: Students use an earthquake model in order to determine whether there are any patterns that would help us determine the time and magnitude of an earthquake. Materials:For each student team: Earthquake Model Meter stick Graph paper Earthquake Model Pre-lab worksheet. Earthquake Model Worksheet 2. Source: adapted by Wendy Van Norden from SERC Grade level: 7-12 Time: Day 1: Intro demo and pre-lab Days 2 and 3: data collection and graphing Day 4: discussion and review Total: approximately 4 class periods Student Learning Outcomes: Students will be able to explain the Elastic Rebound Theory of earthquakes. Students will use a model to simulate earthquakes. Students will graph data from the model experiments. Students will look for patterns in the graphs and apply those pattern to our ability to predict earthquakes. Students will consider the value of using models in order to understand natural processes. Lesson format: Laboratory experiment Standards Addressed: This lesson assists learners in developing proficiency in NGSS Performance Expectation MS-ESS3-2 (Analyze and interpret data on natural hazards to forecast future catastrophic events and inform the development of technologies to mitigate their effects.). This lesson and its further investigations assists learner by including all eight practices of science and engineering that the NGSS Framework identifies as essential for all students to learn and describes in detail as listed below: 1. Asking questions (for science) and defining problems (for engineering) 2. Developing and using models 3. Planning and carrying out investigations 4. Analyzing and interpreting data 5. Using mathematics and computational thinking 6. Constructing explanations (for science) and designing solutions (for engineering) 7. Engaging in argument from evidence 8. Obtaining, evaluating, and communicating information.

DIRECTIONS:

Start learning about earthquakes and the scientists who research them by having class watch the When Nature Strikes: Earthquakes video.

This activity is designed to follow a unit on plate tectonics, for it assumes a basic understanding of plate movement. In this model, the number of clicks of the winch tells us how much stress is added. Since stress is added to a fault every year, the number of clicks will stand in for number of years between earthquakes. If the brick always moves after 10 clicks, then we can predict when the brick will move next. As a model for the real world, that could mean that we could predict that a particular fault will give us an earthquake every 100 years.

The amount of movement of the brick correlates with the magnitude of an earthquake, since the more a fault moves, the more energy is released, and the larger the earthquake magnitude.

In this lab, you are trying to find out whether this model allows us to predict the timing of the earthquake, the magnitude of an earthquake, and whether there is a relationship between the stress and the movement.

The Earthquake Model can be used as a demonstration, especially for students with poor math skills. From a short demonstration with only a few data points, students will conclude that the number of clicks that cause the brick to move is not always the same and the movement of the brick is not always the same. Also, the number of clicks don't seem to correlate with the distance of movement. From that we must conclude that neither the timing of earthquakes not the magnitude of earthquakes can be predicted.

Only with a graph of large data set, can a more interesting relationship be discerned. The points are not entirely random. Instead there is a very weak correlation between the stress and the movement. Also, there is some clumping of data, but still plenty of outliers. Therefore, we cannot predict the time of an earthquake yet we can conclude that if more stress is accumulated, then an earthquake is somewhat more likely, and is somewhat more likely to be a larger earthquake. The messy clumping of data allows us to conclude that most earthquakes will occur within a certain range. Older students may use Excel to graph, and it would be easier to graph a much larger data set. They may also use Excel to determine the R2 value of the trend line. The R2 value of a perfect correlation is 1.0, and the R2 value of random data is 0. The data from the Earthquake tends to result in an R2 value of 0.50, indicating a very weak correlation. In addition, there will be some clumping of data.

For detailed instructions about graphing and generating an R2 value in Excel, go to Excel

When demonstrating the use of the model before the pre-lab, explain that your first earthquake data point is not valid since you placed the brick in an arbitrary location. Do not demonstrate more than two earthquakes for the pre-lab.

ASSESSMENT:

Assess student worksheets and graph.

CLEAN-UP:

None

EXTENSIONS:

For Further Investigation
• Find the effect of a change in the amount of friction by using talcum powder on the board instead of sandpaper and determine how that would relate to real earthquakes.
• Find the effect of increased mass by adding bricks and determine what factors are changed by the addition of bricks and how that relates to real earthquakes.
• Attach a second brick behind the first with a bungee cord, and see how one earthquake can affect another. Can you predict the relationship?

BACKGROUND INFORMATION:

Most earthquakes are the result of plate movements. At plate boundaries, plates are either moving towards each other, away from each other, or past each other. However, they usually don't move smoothly. Usually the plate boundaries are stuck together by friction. However, the stress from plate tectonics continues to build up on the locked plates. As the stress of the movement increases, the rocks of the earth are able to deform, similar to the way a rubber band will stretch as it is pulled. Just as a rubber band will eventually break with too much stress, the rocks eventually break, releasing the pent up energy in the form of earthquake waves. The break in the rock along which movement has taken place is called a fault. This explanation of earthquakes is called the Elastic Rebound Theory.

After an earthquake the stress will be applied again, the rocks will deform and finally break, causing another earthquake. If we knew the amount of stress, the elasticity of the rocks, and the time since the last earthquake, could we predict the next earthquake in an earthquake cycle?

It is difficult to know much about rocks that are kilometers underground, but we can simplify the process with a model. In this lab, we are going to use an earthquake model. A winch will produce the stress that will be pulling a brick that represents the rocks of the Earth. The winch makes clicks at regular intervals, so by counting the number of clicks, we can quantify the amount of stress added. In the real world, we know that more stress is added each year. In our model, we know that more stress is added with each click of the winch, so the number of clicks represents the number of years between earthquakes.

The winch will be connected to the bricks with elastic surgical tubing. Eventually the strain within the stretched surgical tubing will be greater than the friction holding the brick to the table, and the brick will move, just like a fault moves when it is under too much stress so it breaks. The more energy released in the movement, the farther the brick will move. In the real world, the more a fault moves, the greater the magnitude of earthquake. We will attempt to determine the relationship between the stress applied by the winch and the size of the earthquake, as measured by the distance of the moved brick.

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