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1 Chapter Outline Earthquakes CHAPTER 6 Lesson 1: Earthquakes and Plate Boundaries A. What is an earthquake? 1. A(n) is the rupture and sudden movement of rocks along a fault. A fault is a fracture surface along which rocks can slip. 2. Energy stored as a change in shape is called. a. and matter move through Earth s mantle by convection. Some heat energy from Earth s interior is transformed into energy. b. Some of the kinetic energy in Earth s mantle creates in rocks. 3. Elastic strain builds up in along faults as the rocks move past each other. When rocks cannot stretch to add more, they release energy by and slipping. 4. When rocks along a fault suddenly break or slip, elastic strain is released. Complex released. radiate in all directions, carrying some of the 5. Plate boundaries are often that are km wide, rather than a single fault. 6. The of an earthquake is the place on a fault where the rupture and movement of the earthquake begins. B. Plate Boundaries and Earthquakes 1. Most, but not all, earthquakes occur at. The three different types of plate boundaries have different usual patterns of. a. Most earthquakes at occur at relatively shallow depths and are relatively weak earthquakes. b. At transform plate boundaries, most earthquakes occur on faults and at relatively depths. Earthquakes with a(n) focus can produce severe shaking, and so dangerous earthquakes can occur at transform plate boundaries. 42 Earthquakes

2 c. Earthquakes at convergent plate boundaries tend to be the earthquakes. They have been some of the most destructive earthquakes in human history. 2. A small percentage of earthquakes occur away from. These earthquakes can be destructive because people are often unprepared for them. Lesson 2: Earthquakes and Seismic Waves A. What are seismic waves? 1. are waves of energy produced at the focus of an earthquake as elastic strain is released. a. Seismic waves travel in all directions from the of an earthquake. b. The amount of energy carried by seismic waves as the waves move away from the focus. This is because rocks as the seismic waves pass through them. some energy 2. The of an earthquake is the point on Earth s surface directly above the focus of the earthquake. B. Types of Seismic Waves 1. There are different types of seismic waves: primary waves, secondary waves, and surfaces waves. a. are compressional waves that move rocks and other matter parallel to the direction the wave is traveling. Primary waves are the fastest seismic waves. b. are shearing waves that move rocks and other matter back and forth perpendicular to the direction the waves are traveling. Secondary waves travel about 60 percent as fast as. c. Some of the energy from P-waves and S-waves that reach Earth s surface can be trapped in the upper areas of Earth s crust to form the type of seismic wave.. Surface waves are d. Surface waves usually cause shaking than P-waves or S-waves, and they are often the most destructive type of seismic wave. C. Using Seismic Wave Data 1. A(n) is a scientist who studies earthquakes. Earthquakes 43

3 2. The you are from the focus of an earthquake, the farther S-waves will be behind the P-waves. 3. Seismic waves change speed and when the material through which they are traveling changes. 4. Observing the paths of seismic waves can help scientists to understand what kind of make up Earth s interior. 5. The is a portion of Earth that does not receive any seismic waves from a particular earthquake. 6. Because S-waves cannot move through and P-waves would be bent by a(n), scientists think Earth s outer core is liquid and causes the. Lesson 3: Measuring Earthquakes A. How are earthquakes measured? 1. Scientists determined the size of the large earthquake that occurred in the Ocean on December 26, 2004, by measuring how much the rock moved along the where the earthquake started. 2. Because the earthquake occurred, the movement of rock caused a huge ocean B. Recording Seismic Waves in the Indian Ocean. 1. A(n) is an instrument used to record and measure movements of the ground caused by seismic waves. a. Seismographs record the size, direction, and time of the movements caused by different types of. b. Seismographs record ground motion in two orientations:, or back-and-forth, and, or up-and-down. 44 Earthquakes

4 2. The record of the seismic waves created by a seismograph is called a(n). a. The x-axis of a seismogram represents. b. Heights of waves on a seismogram show the relative size of ground caused by seismic waves. C. Locating an Epicenter 1. With readings from at least seismographs, you can use triangulation to find the location of the of an earthquake. a. Use a seismogram to measure the number of between the arrival of P-waves and the arrival of S-waves. b. Use a graph showing the between P- and S-waves plotted against distance to determine how far the waves traveled. c. On a map, draw a(n) with a radius equal to the distance the waves have traveled around the location of the seismograph. d. Draw the same kind of circles for additional seismographs. The location of the D. Measuring Earthquake Size will be shown by the intersection of the circles. 1. The scale is based on a seismogram s record of the amplitude of ground motion. a. Numerical measurements of magnitude vary from about 0.0 to 9.0, but each one number represents b. Magnitude can also be used to understand the amount of times the amount of ground motion. released by an earthquake. An increase of magnitude scale represents 30 times as much energy being released. unit on the 2. The scale was the first magnitude scale, but is not as accurate as more modern magnitude scales. 3. Today, the most commonly used scale for measuring earthquakes is the scale. Earthquakes 45

5 E. Earthquake Intensity 1. Besides size, earthquakes can also be compared by their, or the amount of damage they cause. 2. Intensity tends to as you move away from the epicenter, but it can vary depending on the types of rocks or sediments in an area. Lesson 4: Earthquake Hazards and Safety A. Earthquake Hazards 1. Most injuries from a(n) are caused by the collapse of buildings and other structures, not directly by the ground shaking. 2. Fires caused by broken or electrical lines are the most common hazard following an earthquake. 3. A(n) is the sudden movement of soil and rocks down a slope. 4. Earthquakes sometimes cause, a process by which shaking makes loose sediment behave like a liquid. Liquefaction near buildings can cause them to sink into the ground. 5. An ocean wave caused by an earthquake is called a(n) wave, or a. a. Like seismic waves, tsunamis carry energy, but they can also cause flooding and carry objects in the they move. b. Just before a tsunami strikes, water along a(n) sometimes moves quickly toward the sea, exposing areas that are usually underwater. B. Avoiding Earthquake Hazards 1. The chance of earthquake damage is greatest close to and also increases in areas where Earth s surface is made of rather than solid rocks. sediments 2. showing where the chance of earthquake damage is greatest, such as in areas along the San Andreas Fault, can help in the planning of safe ways to use land. 46 Earthquakes

6 C. Earthquakes and Structures 1. Tall buildings or structures and buildings made of materials usually suffer the most damage in an earthquake. Structures made from flexible building materials, such as, usually suffer less damage. 2. Some buildings in areas threatened by earthquakes are supported by, circular moorings placed under the buildings. These moorings act like shock absorbers for the buildings. D. Earthquake Safety 1. To be as safe as possible during and after an earthquake, it is important to prepare of time. a. With your family,, review, and practice an earthquake disaster plan. b. Make an earthquake supply kit with canned food, water, a batterypowered, a flashlight, and first aid supplies. c. Move objects close to the ground, and learn how to shut off gas, water, and in your home. 2. During a(n), stay indoors, get away from anything that could break or fall on you, and find something sturdy to hide underneath. Earthquakes 47

Section Forces Within Earth. 8 th Grade Earth & Space Science - Class Notes

Section Forces Within Earth. 8 th Grade Earth & Space Science - Class Notes Section 19.1 - Forces Within Earth 8 th Grade Earth & Space Science - Class Notes Stress and Strain Stress - is the total force acting on crustal rocks per unit of area (cause) Strain deformation of materials