Source: D4K: “Earthquakes”
Visit the D4K companion Web site to learn more about Earthquakes: D4K: “Earthquakes”
This video segment from IdahoPTV's D4K describes the structure of the earth and how the movement of tectonic plates causes earthquakes, defines epicenter, seismograph, intensity and shows the tools scientists use to study earthquakes. It answers the questions, "Can we predict when they will happen?" There are photos of the San Francisco Earthquake of 1906, and the Idaho earthquake of 1983 and the video encourages you to be prepared and have an emergency plan if one should occur.
JOAN CARTAN-HANSEN: The Earth is made up of 3 main layers: The center – the core – which is very hot. Around the core lies the mantle, a thick layer of mostly rock and some liquid. And floating on top of the mantle is the earth’s thin outer layer called the crust. The crust is made up of separate slabs called tectonic plates. The solid rock of the crust is under constant pressure from the movement of the plates. As a result giant cracks or fault lines are created. When plates try to slide past each other along a fault line sometimes they get stuck. The pressure builds up until the plates suddenly break apart causing a powerful ground movement we call an earthquake.
CHILD: You can see why an earthquake can cause a lot of damage.
Put 2 wood blocks together and cover them with a layer of sand. Put a few buildings and animals on top and then move one of the blocks and that’s what an earthquake looks like.
JOAN: The spot on the Earth’s surface reached by the first wave is called the epicenter. From the epicenter seismic waves or shock waves spread outward.
Scientists measure earthquakes with a special tool called a seismograph. The seismograph’s pin records shock waves by drawing lines on a piece of paper. When a wave is closer or stronger the line is longer. When the wave is farther away or weaker the line is shorter.
Another thing scientists look for is the intensity and magnitude of an earthquake. The intensity is the damage that people can see and feel. The magnitude is how strong the surface of the earth shakes.
CHILD: Scientists use a special scale called a Richter scale to measure the intensity and magnitude of an earthquake -the higher the number, the more severe the earthquake. Say this marble represents a magnitude one earthquake and a golf ball would be 3, a baseball would be a 4 and soccer ball would be a 5.
The largest earthquake in the world so far happened in Chile in February of 2010. That quake measured 9.5 on the Richter scale, so if it were a ball it would be about this size.
JOAN: One of the most famous earthquakes in U.S. history was the 1906 earthquake in San Francisco. That earthquake leveled 500 city blocks, killed 3,000 people and left 225,000 people homeless.
One of the largest earthquakes in Idaho history was the 1983 quake near the town of challis. Two children died when a storefront collapsed on top of them. And in that quake MT. Borah, Idaho’s highest peak rose about a foot and it fell back into place.
Earthquakes just don’t happen on land. They can happen in the ocean too and can be just as destructive. The shifting of the ocean floor can cause a giant wave called a tsunami.
Because a tsunami contains so much energy it can race across the ocean for thousands of miles at speeds of more than 500 miles per hour. And when it reaches land, the height of the wave can be over 100 feet tall.
Scientists have no way of predicting earthquakes so it’s a good idea to have a disaster kit at home.
You should have a fire extinguisher, a first aid kit and enough water so everyone in your family can have enough to drink for 3 days.
You should have an emergency plan so everyone knows where to meet after an earthquake. And make sure you or your parents have a person out of town you can contact so they can let everybody else know you’re okay.
During an earthquake if you’re inside, get under a strong table or stand in a doorway and stay away from windows. And if you’re outside, stay away from buildings, trees and power lines.
Scientists are studying earthquakes in hopes of someday learning how to predict when they will happen. That could save lots of lives. But for now, we don’t know when the next earthquake will strike.
The best thing you can do is find out what an earthquake is and then be prepared.
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