Chapter 11 Chapter 11 EarthquakesEarthquakes

Study GuideStudy Guide

Earthquake CausesEarthquake Causes There is a limit to how far rocks can bend There is a limit to how far rocks can bend

and stretch due to the motions of the and stretch due to the motions of the plates. This is called the elastic limit. plates. This is called the elastic limit. Once the elastic limit is passed the rocks Once the elastic limit is passed the rocks may break.may break.

An earthquake is the vibrations produced An earthquake is the vibrations produced by the breaking of rock. Most earthquakes by the breaking of rock. Most earthquakes result from rocks moving over, under, or result from rocks moving over, under, or past each other along fault surfaces.past each other along fault surfaces.

Types of FaultsTypes of Faults Three types of forces Three types of forces

act on rocks-tension, act on rocks-tension, compression, and compression, and shear.shear.

Tensional forces cause Tensional forces cause rocks to be pulled rocks to be pulled apart. Tension causes apart. Tension causes normal faults.normal faults. Along a normal fault, the Along a normal fault, the

rock above the fault rock above the fault surface moves downward surface moves downward in relation to the rock in relation to the rock below the fault surface.below the fault surface.

Types of FaultsTypes of Faults

Compressional Compressional forces squeeze forces squeeze rock. Compression rock. Compression causes reverse causes reverse faults. faults.

-The rock above a -The rock above a reverse fault is reverse fault is forced up and over forced up and over the rock below the the rock below the fault surface.fault surface.

Types of FaultsTypes of Faults Shear is a force that Shear is a force that

causes rocks on causes rocks on either side of a fault either side of a fault to slide past each to slide past each other.other.

-At a strike-slip fault, -At a strike-slip fault, rocks on either side rocks on either side of the fault are of the fault are moving past each moving past each other without upward other without upward or downward or downward movement.movement.

Features of EarthquakesFeatures of Earthquakes

Seismic waves are waves of energy Seismic waves are waves of energy generated by an earthquake. During a generated by an earthquake. During a strong earthquake, the surface of the strong earthquake, the surface of the ground can ripple like waves do in ground can ripple like waves do in water.water.

The point where this energy release The point where this energy release first occurs is the focus of the first occurs is the focus of the earthquake. Seismic waves are earthquake. Seismic waves are produces and travel outward from the produces and travel outward from the earthquake focus.earthquake focus.

Features of an Features of an EarthquakeEarthquake

When earthquakes occur, three When earthquakes occur, three different types of seismic waves are different types of seismic waves are produced. All of the waves are produced. All of the waves are generated at the same time, but generated at the same time, but each behaves differently.each behaves differently.

Features of an Features of an EarthquakeEarthquake

Primary waves (P-Primary waves (P-waves) cause waves) cause particles in rocks to particles in rocks to move back and move back and forth in the same forth in the same direction that the direction that the wave is traveling. wave is traveling. This is the same This is the same way that a wave way that a wave travels through a travels through a coiled spring.coiled spring.

Features of an Features of an EarthquakeEarthquake

Secondary waves Secondary waves (S-waves) move (S-waves) move through the earth through the earth causing particles causing particles in rocks to move at in rocks to move at right angles to the right angles to the direction of wave direction of wave travel. This is like travel. This is like a wave traveling a wave traveling through rope.through rope.

Features of an Features of an EarthquakeEarthquake

Surface waves cause Surface waves cause move of the move of the destruction. These destruction. These waves move rock waves move rock particles in a particles in a backward rolling backward rolling motion.motion.

Surface waves are Surface waves are produces when produces when earthquake energy earthquake energy reaches the surface reaches the surface of Earth.of Earth.

Features of an Features of an EarthquakeEarthquake

The earthquake The earthquake epicenter is the epicenter is the point of the Earth’s point of the Earth’s surface directly surface directly above the focus. above the focus. Surface waves Surface waves travel outward travel outward from the epicenter.from the epicenter.

Locating and EpicenterLocating and Epicenter The seismic waves travel The seismic waves travel

through earth at through earth at different speeds. different speeds. Primary waves are the Primary waves are the fastest, secondary waves fastest, secondary waves are slower, and surface are slower, and surface waves are the slowest.waves are the slowest.

Seismic waves from Seismic waves from earthquakes are earthquakes are measured with a measured with a seismograph. seismograph. Seismographs register Seismographs register waves and record the waves and record the time that each arrives.time that each arrives.

Locating and EpicenterLocating and Epicenter The difference in arrival The difference in arrival

times of the three times of the three different seismic waves different seismic waves at seismograph stations at seismograph stations is used to calculate the is used to calculate the distance from the distance from the station to the station to the earthquake epicenter.earthquake epicenter.

To find the location of To find the location of an epicenter, readings an epicenter, readings are needed from a are needed from a minimum of three minimum of three seismograph stations.seismograph stations.

Locating and EpicenterLocating and Epicenter By studying seismic By studying seismic

waves that have traveled waves that have traveled through earth, scientists through earth, scientists were able to map Earth’s were able to map Earth’s internal structureinternal structure-Secondary waves are -Secondary waves are not transmitted through not transmitted through liquid, so they stop when liquid, so they stop when they hit the liquid outer they hit the liquid outer core.core.-Primary waves are -Primary waves are slowed and bent by the slowed and bent by the liquid outer core. P-liquid outer core. P-waves speed up again as waves speed up again as they travel through the they travel through the solid inner core.solid inner core.

People and EarthquakesPeople and Earthquakes The measure of the energy The measure of the energy

released from an earthquake is released from an earthquake is called its magnitude.called its magnitude.

The Richter magnitude scale is The Richter magnitude scale is used to describe the strength of used to describe the strength of an earthquake and it is based on an earthquake and it is based on the height of the lines on a the height of the lines on a seismogram.seismogram.-The Richter scale has no upper -The Richter scale has no upper limit, though scientists think limit, though scientists think that a value of 9.5 would be the that a value of 9.5 would be the maximum strength that an maximum strength that an earthquake could register.earthquake could register.

Richter ScaleRichter Scale

People and EarthquakesPeople and Earthquakes Tsunamis are ocean Tsunamis are ocean

waves caused by waves caused by earthquakes.earthquakes. An earthquake under An earthquake under

the ocean causes a the ocean causes a sudden violent sudden violent movement of the movement of the ocean floor. This ocean floor. This movement pushes movement pushes water and causes a water and causes a powerful wave that powerful wave that can travel thousands can travel thousands of kilometers in all of kilometers in all directions.directions.