Seismic Waves Work Sheet

Seismic Waves

Your Name: Eugenia Meanus Concept(s) Addressed: When displacement occurs along a fault, the built up strain e energy is released in the form of seismic waves Lab Goals: Students will differentiate between P- and S-waves using a slinky. Lab Objectives: Students will: . Make oscillating waves with a slinky, simulating an ‘S’ wave. . Make oscillating waves with a slinky, simulation an ‘P’ wave. Benchmark(s) Addressed: 5.2 Interaction and Change: Force, energy, matter, and organisms interact within living and non-living systems.

5.2P.1 Describe how friction, gravity, and magnetic forces affect objects on or near Earth. 5.3 Scientific Inquiry: Scientific inquiry is a process of investigation based on science principles and questioning, collecting, describing, and examining evidence to explain natural phenomena and artifacts.

5.3S.1 Based on observations and science principles, identify questions that can be tested, design an experiment or investigation, and identify appropriate tools. Collect and record multiple observations while conducting investigations or experiments to test a scientific question or hypothesis. Materials and Costs: List the equipment and non-consumable material and estimated cost of each Item...... $ Slinkies (15- at Toys R Us)...... $74.85 Estimated total, one-time, start-up cost:...... $74.85 Activity Sheets (provide by school)...... $0 Time: Preparation time: 10 minutes Instruction time: 30 minutes. The power point will take about 20 minutes. (There is a total of 4.5 minutes of you tube videos.) The actual activity will take about 10 minutes. Clean-up time: 10 minutes or less.

Background:

Seismograms, obtained from seismographs housed at seismic stations, provide a great deal of information about the behavior of seismic waves. Seismic waves are waves of elastic energy that radiate out in all directions from the site where an earthquake occurs (the focus.) We will be concentrating on body waves, but there are many other types of waves produced by an earthquake. P and S waves are the two main types of body waves.

P or Primary waves (A in figure below) are waves of compression. They push and pull rocks in the direction the wave is traveling. They are the faster of the two types of waves we will study today, and they arrive at the seismic station before the S wave. Have two students hold either end of a slinky so that the slinky is stretched out almost horizontally. This can be done on the surface of a desk. Have one of the students push a wave toward the other. You could also have one of the students pull a wave. P waves travel through liquid, solid, and gas (all of which are compressible.)

S or secondary waves (B in figure below) are shearing waves. The S wave moves the material at right angles to the direction that the wave is traveling. This can be illustrated by the slinky or by a piece of rope. Again, have two students hold either end of a slinky so that the slinky is stretched out almost horizontally. Shake one end of the slinky or rope while holding the other end taut. S waves do not travel through liquids or gasses as liquids and gasses do not resist changes in shape.

The difference in arrival times of the first P and S waves is used with a travel time graph (travel time versus distance to epicenter) to determine how far the waves have traveled from the earthquake's epicenter. When this distance is determined, a circle with a certain radius (that determined distance) is drawn around the seismic station. Remember that on a globe it will appear circular, but on a map projection (we are using a Mercator projection) it will not appear as a circle unless the seismic station is located toward the center of the map and very near to the earthquake's epicenter. You will need to use at least three seismic stations to determine the location (where the three radii intersect) of the earthquake through triangulation.

Procedure:

Allow students to briefly experiment with P and S waves. For P waves, have two students hold either end of a slinky so that the slinky is stretched out almost horizontally. This can be done on the surface of a desk. Have one of the students push a wave toward the other. You could also have one of the students pull a wave. For S waves, again, have two students hold either end of a slinky so that the slinky is stretched out almost horizontally. Shake one end of the slinky or rope while holding the other end taut. P waves are compressional waves and are faster than S waves. They arrive at the seismic station first. S waves are shear waves and they are slower than P waves. They arrive at the seismic station after the P wave. S waves do not travel through liquid or gas, while P waves can (but they are refracted{bent}). This is because gas and liquids can be compressed, but not sheared. This becomes very important when explaining the "quiet zone" or the "shadow zone of the Earth's core" on the opposite side of the Earth (more than 11,000 km away) as the earthquake's epicenter. Seismographs on the opposite side of the Earth can't pick up S waves and therefore it is impossible to determine the distance from the site with the seismogram. Also, the P waves they receive have been refracted. This is due to the liquid outer core of the Earth

Assessment: Class discussion and answering the questions on the work sheet below. Students' summarize what they have learned about seismic body waves. What are the differences between P and S waves?

Citations: http://visearth.ucsd.edu/VisE_teach/lessons/seismic_LP.html http://web.ics.purdue.edu/~braile/edumod/slinky/slinky.htm Seismic waves Work Sheet

The shaking experiences during earthquake is caused by a release of built up elastic strain energy. You can hold a yardstick over the edge of a table and vibrate it by bending it and letting go. If we bend it too far, it will break.

 What determines when the ruler will break?  In the Earth, what determines when the crust will break?  After the Earth breaks, what kind of structure is formed?

(Review the 3 main types of faults, thrust, normal, strike-slip)

When displacement occurs along a fault, the built up strain e energy is released in the form of seismic waves. There are two types of body waves, S-Waves and P-Waves.

Our goal is to discover the difference between P- and S-waves using a slinky.

A stretched out slinky can help show how each type of seismic wave can propagate. Have one person hold each end..

P-waves Use a quick pulsing motion to initiate a wave down the spring. Try 2 different ways of doing this:

 by pushing a wave  by pulling a wave

Put a small piece of tape on the slinky and notice which direction the tape moves as the wave pass through. Describe and illustrate this motion, is the vibration direction parallel or perpendicular to the direction of the wave moves?

S-waves Using a side to side motion generate another type of wave in the slinky.

Describe and illustrate this motion, is the vibration direction parallel or perpendicular to the direction of that the wave moves?

Summarize what you know about seismic body waves.