Earthquakes

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Earthquakes :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–1 Earthquakes An earthquake is the shaking and trembling that results from the sudden movement of part of the Earth’s crust. The most common cause of earthquakes is faulting. During faulting, energy is released. Rocks continue to move until the energy is used up.

Slide 2:

Focus :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–3 Focus Most faults occur between the surface and a depth of 70 kilometers. The point beneath the surface where the rocks break and move is called the focus. The focus is the underground origin of an earthquake.

Epicenter :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–4 Epicenter Directly above the focus, on the Earth’s surface is the epicenter. Earthquake waves reach the epicenter first. During an earthquake, the most violent shaking is found at the epicenter. Map of Epicenter, KY, TN

The power of Earthquakes :

Collapsed Cypress Freeway :

Map of Worldwide Earthquakes :

Global Distribution of Earthquakes :

Earthquake Belts :

Slide 10:

Three Types of Faults :

Slide 12:

Slide 13:

Thrust Fault Example :

Total Slip in the M7.3 Landers Earthquake :

Slip on an earthquake fault :

Slip on an earthquake faultSecond 2.0 :

Slip on an earthquake faultSecond 4.0 :

Slip on an earthquake faultSecond 6.0 :

Slip on an earthquake faultSecond 8.0 :

Slip on an earthquake faultSecond 10.0 :

Slip on an earthquake faultSecond 12.0 :

Slip on an earthquake faultSecond 14.0 :

Slip on an earthquake faultSecond 16.0 :

Slip on an earthquake faultSecond 18.0 :

Slip on an earthquake faultSecond 20.0 :

Slip on an earthquake faultSecond 22.0 :

Slip on an earthquake faultSecond 24.0 :

Bigger Faults Make Bigger Earthquakes :

Bigger Earthquakes Last a Longer Time :

What Controls the Level of Shaking? :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–31 What Controls the Level of Shaking? Magnitude More energy released Distance Shaking decays with distance Local soils amplify the shaking

Is there such a thing as “Earthquake Weather”??? :

Earthquake Effects - Ground Shaking :

Earthquake Effects - Surface Faulting :

Earthquake Effects - Liquefaction :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–35 Earthquake Effects - Liquefaction Source: National Geophysical Data Center Niigata, Japan 1964 Earthquakes affects Liquefaction

Earthquake Effects - Landslides :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–36 Earthquake Effects - Landslides Turnagain Heights, Alaska,1964 (upper left inset); Santa Cruz Mtns, California , 1989 Source: National Geophysical Data Center

Earthquake Effects - Fires :

Earthquake Effects - Tsunamis :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–38 Earthquake Effects - Tsunamis Photograph Credit: Henry Helbush. Source: National Geophysical Data Center 1957 Aleutian Tsunami

Generation of a Tsunami :

Seismic Waves :

Slide 42:

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–42 Seismic waves that travel fastest are P waves. They travel through solids, liquids and gases. They move at different speeds depending on the density of the material through which they are moving. As they move deeper in the Earth they move faster. P waves are push-pull waves. Primary Waves

P Waves :

Secondary Waves :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–44 Secondary Waves Not travel as fast as P waves S waves travel through solids but not liquids or gases. S waves cause particles to move from side to side. They move at right angles to the direction of the wave.

S Waves :

Surface Waves :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–46 Surface Waves The slowest moving seismic waves are called surface waves or L waves. L waves originate on the Earth’s surface at the epicenter. They move along the surface the way waves travel in the ocean. The Earth’s surface moves up and down with each L wave. L waves cause most of the damage.

Two Common Types of Surface Waves :

The Seismograph :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–48 The Seismograph Invented in 1893 by John Milne. measures seismic waves. A weight attached to a spring remains nearly still even when the Earth moves. A pen attached to the weight records any movement on a roll of paper on a constantly rotating drum. The drum moves with the Earth and affects the line.

Functioning of Seismograph :

Seismologists :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–50 Seismologists Seismologists study earthquakes. They can determine the strength of an earthquake by the height of the wavy line recorded on the paper. The seismograph record of waves is called a seismogram. The Richter scale is used to calculate the strength of an earthquake.

Slide 51:

The Richter Scale :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–52 The Richter Scale The amount of damage created by an earthquake depends on several factors. The earthquake’s strength The kind of rock and soil that underlie an area The population of the area The kind of buildings in the area The time at which the earthquake occurs

Predicting Earthquakes :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–53 Predicting Earthquakes Scientists have identified warning signals the help predict earthquakes with greater accuracy. Often changes occur in the speed of P and S waves before an earthquake occurs. Sometimes slight changes in the tilt of the Earth’s surface can be detected. Some scientists believe animals behavior is affected.

Elevated Freeway Collapse in Kobe :

Earthquake Effects, San Francisco’s Fisherman’s Wharf District, 1906 :

Earthquake Depth and Plate Tectonic Setting :

Earthquake Depth and Plate Tectonic Setting

Earthquake Depth and Plate Tectonic Setting, Selfos, Iceland (June 200) :

Effects of Mexico City Earthquake :

San Andreas Fault :

Copyright © Houghton Mifflin Company. All rights reserved. Geology, 10a–59 San Andreas Fault The San Andreas fault extends 960 km from Mexico to the north of California. The land to the west is moving north. The land to the east of the fault is moving south. All the rocks do not move at the same time so earthquakes occur in one area and then another.

San Francisco Quake :

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