2 Earthquake CausesThere is a limit to how far rocks can bend and stretch due to the motions of the plates. This is called the elastic limit. Once the elastic limit is passed the rocks may break.An earthquake is the vibrations produced by the breaking of rock. Most earthquakes result from rocks moving over, under, or past each other along fault surfaces.
3 Types of FaultsThree types of forces act on rocks-tension, compression, and shear.Tensional forces cause rocks to be pulled apart. Tension causes normal faults.Along a normal fault, the rock above the fault surface moves downward in relation to the rock below the fault surface.
4 Types of FaultsCompressional forces squeeze rock. Compression causes reverse faults.-The rock above a reverse fault is forced up and over the rock below the fault surface.
5 Types of FaultsShear is a force that causes rocks on either side of a fault to slide past each other.-At a strike-slip fault, rocks on either side of the fault are moving past each other without upward or downward movement.
6 Features of Earthquakes Seismic waves are waves of energy generated by an earthquake. During a strong earthquake, the surface of the ground can ripple like waves do in water.The point where this energy release first occurs is the focus of the earthquake. Seismic waves are produces and travel outward from the earthquake focus.
7 Features of an Earthquake When earthquakes occur, three different types of seismic waves are produced. All of the waves are generated at the same time, but each behaves differently.
8 Features of an Earthquake Primary waves (P-waves) cause particles in rocks to move back and forth in the same direction that the wave is traveling. This is the same way that a wave travels through a coiled spring.
9 Features of an Earthquake Secondary waves (S-waves) move through the earth causing particles in rocks to move at right angles to the direction of wave travel. This is like a wave traveling through rope.
10 Features of an Earthquake Surface waves cause move of the destruction. These waves move rock particles in a backward rolling motion.Surface waves are produces when earthquake energy reaches the surface of Earth.
11 Features of an Earthquake The earthquake epicenter is the point of the Earth’s surface directly above the focus. Surface waves travel outward from the epicenter.
12 Locating and Epicenter The seismic waves travel through earth at different speeds. Primary waves are the fastest, secondary waves are slower, and surface waves are the slowest.Seismic waves from earthquakes are measured with a seismograph. Seismographs register waves and record the time that each arrives.
13 Locating and Epicenter The difference in arrival times of the three different seismic waves at seismograph stations is used to calculate the distance from the station to the earthquake epicenter.To find the location of an epicenter, readings are needed from a minimum of three seismograph stations.
14 Locating and Epicenter By studying seismic waves that have traveled through earth, scientists were able to map Earth’s internal structure-Secondary waves are not transmitted through liquid, so they stop when they hit the liquid outer core.-Primary waves are slowed and bent by the liquid outer core. P-waves speed up again as they travel through the solid inner core.
15 People and Earthquakes The measure of the energy released from an earthquake is called its magnitude.The Richter magnitude scale is used to describe the strength of an earthquake and it is based on the height of the lines on a seismogram.-The Richter scale has no upper limit, though scientists think that a value of 9.5 would be the maximum strength that an earthquake could register.
17 People and Earthquakes Tsunamis are ocean waves caused by earthquakes.An earthquake under the ocean causes a sudden violent movement of the ocean floor. This movement pushes water and causes a powerful wave that can travel thousands of kilometers in all directions.