Weekly Online Lesson Online Lesson Archive Grade Level: 7-12 Subject: Geology

Get Ready to Rumble

On the final day of February, a powerful force rolled into Seattle and shook things up, scaring thousands of people and causing billions of dollars in damage. But this was no gang of thugs that ripped through the Pacific Northwest in only a few minutes' time; it was just Mother Nature.

This 6.8-magnitude earthquake was not a complete surprise to long-time residents, though. Similar quakes hit the Seattle area in 1965 and 1949. By nature of the region's geology, the area periodically experiences earthquakes. The tension and subsequent slippage of Earth's crustal plates as they move over one another causes hard jolts that often rupture landscapes. Fortunately, no one was killed during the Wednesday morning rumble, and although the event devastated most older buildings, newer, quake-resistant structures endured it nearly unscathed.

In this week's lesson, you'll get under the Earth's skin and learn about the geology of earthquakes, how scientists track tremors and consider how quake-area residents cope with living on shaky ground.

A Deeper Understanding

The most widely-accepted theory about what causes the majority of earthquakes worldwide is called Plate Tectonics. Basically, the pieces, or plates, of the Earth's broken-up crust move around and collide with each other, often causing dramatic shifts in the local landscape, increased volcanic activity and the building of mountains.

To start this week's lesson, visit the U.S. Geological Survey's (USGS) site called This Dynamic Earth: the Story of Plate Tectonics. First read the Preface as an introduction to this site and the theory of Plate Tectonics. Then move on to the Historical Perspective section, which provides an overview of the Earth's geological history as scientists understand it — from the single continent of Pangaea to present-day continental separation, and visit the sidebars, such as Inside the Earth. Also read the section, What is a tectonic plate? and check out the sidebar's diagrams demonstrating the Shrinking Farallon Plate, the main cause of the Pacific Northwest region's rumblings. Explore a few of the other pages too, including Understanding plate motions and Plate tectonics and people. You can also view a Java applet of the Tectonic Timeline that illustrates plate movements along the U.S. Pacific Coast over millions of years.

The Earth's Faults

These earthquakes are in no way preventable, but thanks to scientists who observe, record and understand these rumblings of Mother Nature, they continue to improve their abilities to predict earthquakes and figure out ways to resist the severe structural damage caused by them.

Scientists have classified earthquakes into three basic types. View the Fault Motion animations of each of these and photo examples of Faults and Fault Zones. Also, visit USGS to find out more about the San Andreas Fault.

Getting the Shakes

Since the science of seismology is an important specialty for understanding how the Earth moves, literally, learn about the Drum Recorders that map the seismic waves and review a primer on Seismology hosted by Michigan Tech's Geological & Engineering Sciences department. Then visit the Geo-Labs On-Line Project's Virtual Earthquake site, click on Execute Virtual Earthquake and create your own rumble, while you learn about the energy waves that earth movements produce and the seismograms that record those waves.

Then go to the USGS Earthquake Hazards Program site, and focus on the Earthquake Activity page. Click on the region where you live to find out where the nearest seismic activity has been happening. What magnitude of earthquakes have occurred in your area? Why have some locations experienced stronger seismic activity than others? Also, check out the site's Past & Historical Earthquakes page and find out more about some of the world's biggest quakes. Where are these locations compared to tectonic plate interaction points? How do you think a country's economy and architectural technology influences the amount of damage created by a quake?

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