focus seismic waves Earthquakes

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1 LESSON 3 fault line All of a sudden, Earth s crust shakes and solid land shifts. What causes an earthquake? How can an earthquake be measured? Read this selection to learn about earthquakes. Earthquakes The Making of an Earthquake An earthquake is a sudden movement of Earth s crust. Most earthquakes occur along a fault, or a break in Earth s crust. The line where the fault shows on the Earth s surface is the fault line. Rocks along a fault may have been pushing against one another for years. Finally, the forces can grow so strong that the rocks suddenly move or break. This Along this fault, rocks are sliding and sudden movement causes shock pushing against one another. waves. Shock waves are back-and-forth or up-and-down movements, like waves in water. When these reach the surface, an earthquake occurs. Source of an Earthquake The source of an earthquake is usually deep in Earth s crust. The point underground where the earthquake begins is its. Shock waves move out from the. Scientists use the term to name the from an earthquake. 16 Earthquakes

2 On the Surface The point on Earth s surface right above the is the of the earthquake. Seismic waves first reach the surface at the. Therefore, the usually has the most damage. Measuring an Earthquake A tool called a measures and records the strength of. It also records the time of an earthquake. This information helps scientists know where the earthquake started. It also gives the, or strength of the earthquake. Magnitude is a measure of the amount of energy released by an earthquake. Scientists use the to compare earthquakes. The measures an earthquake s. On the, a higher number means a stronger earthquake. An earthquake with a of 1 or 2 on the is a. A is a small shaking that most people would not even feel. An earthquake with a of 9 is the largest ever recorded. Earthquakes with s over 6 generally cause a huge amount of damage. After a large earthquake, a smaller earthquake may occur. It is called an. An can increase the damage that has already occurred. Fault Focus Seismic waves Fault line Epicenter During this earthquake, the rocks on the left moved up, and the rocks on the right slipped down. Earthquake motion Spring Weight Pen Rotating drum This simple can measure the movement of Earth s crust during an earthquake. My Science Vocabulary Go to page 94 to list other words you have learned about earthquakes. Earthquakes 17

3 A. Match each word with its meaning. Write the letter of the correct meaning on the line in front of each word fault line a. the line where a fault shows on Earth s surface b. where an earthquake begins c. produced by an earthquake d. a small shaking of Earth s crust e. the point on Earth s surface above the f. strong energy waves, such as g. a smaller earthquake after a large earthquake h. a scale that measures an earthquake s i. the strength of an earthquake j. a tool that measures and records seismic waves 18 Earthquakes

4 B. Circle the word that makes sense in each sentence. Then write the word. 1. The point on Earth s surface right above the is the (, ). 2. After the first earthquake, an (, ) may occur. 3. Scientists use the (, ) to measure an earthquake s. 4. Shock waves that move out from the of an earthquake are known as (, ). 5. An earthquake that is hardly felt is a (, ). 6. An earthquake begins at the (fault line, ). 7. When rocks along a fault suddenly move or break, (, ) are produced. 8. The tool used to measure and record is a (, ). 9. The line of a fault on Earth s surface is the (, fault line). 10. The amount of energy released by an earthquake is its (, ). WORD ROOT The word seismic is from the Greek word seismos, which means trembling Earth. Earthquakes 19

5 C. Choose the correct vocabulary word to complete each sentence. 1. Seismic waves reach Earth s surface at the. 2. Scientists use the term to name from an earthquake. 3. An earthquake begins underground at the. 4. A very strong earthquake may have a of 9 on the. 5. A fault can be seen on Earth s surface at the. 6. After a large earthquake, an can cause more damage. 7. The strength of an earthquake is its. 8. Scientists use a to measure and record. 9. A sudden movement of rocks along a fault causes, or. 10. The of a is about 1 to 2 on the. 20 Earthquakes

6 D. Use each pair of words in a sentence. 1., 2., 3. fault line, 4., 5., Write! Write your response to the prompt on a separate sheet of paper. Use as many vocabulary words as you can in your writing. Suppose you could follow an earthquake from start to finish. What events would be happening at the source and in the area affected by the earthquake? Earthquakes 21