What is an earthquake?
An earthquake is movement of the earth that causes shaking and rolling of the earth. This is generally the result of movement of the tectonic plates of the earth, though some recent quakes where I live have, some say, been caused by unsafe methods of gas drilling. The link is to a New York Times story with an interactive feature showing the process that may be causing the quakes.
- Google Earth files on earthquakes, including a virtual tour of San Francisco’s 1906 quake, maps, and images of faults.
- A collection of visualizations shows the location and movement of tectonic plates.
- From the same source, links to footage and other visual resources on the 2011 Japan earthquake and tsunami.
- Written in Stone has a series of brief animations showing and explaining what happens during an earthquake. There are animated maps showing the extent of some historical quakes, including the San Francisco earthquake of 1906, and demonstrations of how the earth moves during an earthquake, as well as some showing what happens to buildings during an earthquake.
- More animations, these focusing on the 1906 San Francisco earthquake, plus maps and lots of visual resources including footage of the quake’s damage from the Library of Congress, an Edison newsreel, and Jack London’s album from that event, from GSA.
How do scientists measure earthquakes?
A seismograph is a machine for measuring earthquakes. You can see an animation of a simple seismograph from the Tech Museum, or check out a more thorough page on seismometers.
In ancient China, seismometers were built in the form of big jars with dragons holding balls in their mouths and frogs beneath them to catch the balls, which dropped when there was an earthquake. Download a paper pattern or create your own variant.
Modern seismographs measure earthquakes according to the Richter scale. Charles Richter of the California Institute of Technology developed the scale in 1935. It’s a logarithmic scale, which means that an earthquake measuring 8 on the scale is not just twice as big as one measuring 4. Check out the USGS Earthquakes for Kids website to see recent quakes mapped and find more data and activities on the subject.
A level 2 earthquake is often not felt by people in the area, a level 4 is felt but doesn’t do much damage, a level 6 can do some damage and knock things down, and a level 8 is very serious. The amount of damage depends on a number of factors, though. For example, the New Madrid earthquake of 1811-1812 changed the course of the Mississippi River, cause entire islands in the river to sink, and kept going for three months in a series of quakes which added up to the biggest earthquakes in U.S. history. However, very few people lived in the area at the time, so the damage to buildings and property was not severe. The 1906 earthquake in San Francisco ruined the town and caused enormous damage and loss of life, especially since it was followed by fires. The recent earthquake in Japan was complicated by the presence of nuclear reactors in the area, as well as the tsunami that came with the quake.
How do engineers build with earthquakes in mind?
In earthquake-prone parts of the world, structural engineers and civil engineers work with architects and geologists to make buildings that are less likely to be damaged in earthquakes. Have your students try this out with model buildings and bridges.
- Begin by having students create structures from a choice of materials. Spaghetti, poster board, sugar cubes, Jell-o cubes, pipe cleaners — whatever you can round up. We like to allow open-ended exploration at this point, asking students to keep good records of their observations and processes.
- You can create a shake table in your classroom, or just put your models on an ordinary table and physically shake the table a bit.
- Once the first round of structures has been tested by shaking, have students develop hypotheses about how they could improve their structures for the next round. Have students present their ideas and give one another feedback before they build their second set of structures. You might also like to use the online resources listed below to learn about how engineers have tried to improve earthquake survival of their buildings in the past.
- Test the second set of structures and see whether they survive better. Have students write up a report on their buildings, explaining why their second try was better than the first — or why it wasn’t.
- As a class, list the factors that made a difference in the results of the building experiments, considering the materials, shapes, sizes, construction methods, and any other characteristics that students discovered.
- Individually or as a class, prepare a presentation giving advice to people building structures near earthquake faults.
If you want to work with bridges:
- Bridge to Classroom: Engineering for Earthquakes has basic background info on earthquakes and a bridge building simulation set in Northern California. Students can read about the different types of bridges, “build” their own bridge (complete with construction noises), and then test the bridges under different earthquake conditions. The simulator will explain why the bridge did or did not survive the quake.
- A similar simulator for skyscrapers.
A slideshow of bridges of various kinds. Discuss how each might fare in an earthquake. If possible, discuss bridges in your own town or region, too.
For send-home pages or to add to portfolios, the USGS has sophisticated coloring pages.
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