A Ground-Breaking Revelation: Testing Longitudinal Waves in Different Soil Types *
Did you know that waves travel through the Earth's crust all the time? One major source of these waves is earthquakes, although ground motion can also be caused by something man-made, such as a mine blast or nuclear explosion, or other natural events, such as landslides or volcanic activity.
How does an earthquake cause these waves? The entire outer shell of the Earth, known as the lithosphere, is made up of tectonic plates that are constantly moving. There are seven or eight large tectonic plates and many more minor ones. Where the tectonic plates meet and bump together, it is common to find mountains, volcanic activity, mid-ocean ridges, and earthquakes. (What forms depends on how exactly the tectonic plates are moving against each other at the plate boundary.) The movement of the tectonic plates also causes faults to form, which are cracks in the Earth's surface where a plate, or parts of a plate, moves in different directions. Faults are usually near the edge of a plate. When two tectonic plates (or parts of the same plate) bump or catch as they slide past each other at the fault, earthquakes usually occur. Specifically, as the plates rub together, when they catch and get stuck it results in a build up of pressure because the rocks want to move but cannot. Eventually, some rocks break and the pressure is released as the plates suddenly move. This causes waves of energy, known as seismic waves, to travel through the Earth, making the ground shake. Where the rocks broke is known as the earthquake's focus, and right above this point, up on the ground, is called the earthquake's epicenter.
There are two main types of seismic waves: body waves, which can travel through the inner layers of the Earth, and surface waves, which can only travel on the surface. Body waves are the fastest and have the highest frequency. One type of body wave is called the primary or P-wave. (It is called "primary" because it is the first one you feel in an earthquake.) It pushes and pulls the solid rock or liquid matter that it is moving through, and people feel it as a back-and-forth or side-to-side motion. The P-wave is also what is known as a longitudinal wave, or compression wave. A longitudinal wave is a wave that travels in the same direction as the direction of vibration. Longitudinal waves are around us all the time; other examples of longitudinal waves include an oscillation in a spring, a tsunami wave, and a sound wave.
How well do longitudinal waves, such as from an earthquake, travel in different soil types? In this geology science project, you will answer this by investigating how different types of soil change the amplitude of compression waves. To do this, you will construct a solids wave tank and fill it, one at a time, with different types of soils, such as sandy, clay, or silty soil. For the longitudinal wave source, mount a loudspeaker to the base of the solids wave tank and connect a sound generator and amplifier to the loudspeaker to create vibrations similar to that of an earthquake. (There are softwares available that could be used to initiate the waves and control the amplitude of the loudspeaker, such as FreqGenie.) Measure the amplitude of the waves using an accelerometer connected to computer software that can measure this, such as LoggerPro. You may want to try placing the accelerometer in different positions to ensure that your conclusions are accurate. Which type of soil leads to the smallest amplitudes? Which type leads to the largest amplitudes? How do you think this correlates to how well P-waves from an earthquake travel through different parts of the Earth?
Teisha Rowland, Ph.D., Science Buddies
Cite This Page
Last edit date: 2018-04-12
Here are a few websites that will help you start gathering information about seismic waves, seismology, and different types of soil:
- Nave, C. R. (n.d.). Seismic Waves. HyperPhysics. Department of Physics and Astronomy, Georgia State University. Retrieved March 4, 2013, from http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/seismic.html
- The Seed Site. (n.d.). Soil. Retrieved March 4, 2013, from http://theseedsite.co.uk/soil.html
News Feed on This Topic
- In this science project you investigated how well longitudinal waves travel through different types of soil, but instead of using soil you could try different kinds of substances in your solids wave tank, such as rocks, gelatin, water, or many other possibilities. How well do the longitudinal waves travel through these different substances?
- A seismograph is an instrument used to detect and record seismic waves from earthquakes. Do some background research on seismographs and design a way to use a seismograph to investigate how well longitudinal waves travel through different types of soil.
- If you are interested in this science project, you may also be interested in these other science projects:
Recent Feedback Submissions
|Sort by Date||Sort by User Name|
What was the most important thing you learned?
What problems did you encounter?
Can you suggest any improvements or ideas?
Science Buddies materials are free for everyone to use, thanks to the support of our sponsors. What would you tell our sponsors about how Science Buddies helped you with your project?
Like the TSW selections.
Overall, how would you rate the quality of this project?
What is your enthusiasm for science after doing your project?
Compared to a typical science class, please tell us how much you learned doing this project.
|Do you agree?||Report Inappropriate Comment|
Ask an ExpertThe Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.
Ask an Expert
If you like this project, you might enjoy exploring these related careers:
Soil ScientistNot all dirt is created equal. In fact, different types of soil can make a big difference in some very important areas of our society. A building constructed on sandy soil might collapse during an earthquake, and crops planted in soil that doesn't drain properly might become waterlogged and rot after a rainstorm. It is the job of a soil scientist to evaluate soil conditions and help farmers, builders, and environmentalists decide how best to take advantage of local soils. Read more
Mechanical EngineerMechanical engineers are part of your everyday life, designing the spoon you used to eat your breakfast, your breakfast's packaging, the flip-top cap on your toothpaste tube, the zipper on your jacket, the car, bike, or bus you took to school, the chair you sat in, the door handle you grasped and the hinges it opened on, and the ballpoint pen you used to take your test. Virtually every object that you see around you has passed through the hands of a mechanical engineer. Consequently, their skills are in demand to design millions of different products in almost every type of industry. Read more
GeoscientistJust as a doctor uses tools and techniques, like X-rays and stethoscopes, to look inside the human body, geoscientists explore deep inside a much bigger patient—planet Earth. Geoscientists seek to better understand our planet, and to discover natural resources, like water, minerals, and petroleum oil, which are used in everything from shoes, fabrics, roads, roofs, and lotions to fertilizers, food packaging, ink, and CD's. The work of geoscientists affects everyone and everything. Read more
Mechanical Engineering TechnicianYou use mechanical devices every day—to zip and snap your clothing, open doors, refrigerate and cook your food, get clean water, heat your home, play music, surf the Internet, travel around, and even to brush your teeth. Virtually every object that you see around has been mechanically engineered or designed at some point, requiring the skills of mechanical engineering technicians to create drawings of the product, or to build and test models of the product to find the best design. Read more
News Feed on This Topic
Looking for more science fun?
Try one of our science activities for quick, anytime science explorations. The perfect thing to liven up a rainy day, school vacation, or moment of boredom.Find an Activity