Chapter 10



Chapter 10

Earthquakes

10.1 – How and Where Earthquakes Occur

Vocabulary:

Earthquake: The shaking of Earth’s crust caused by a release of energy. The cause of most earthquakes is the strain (pressure) that builds up along faults at or near boundaries between lithospheric plates.

Fault: A break in the lithosphere along which movement has occurred.

Focus: The point at which the first movement occurs during an earthquake

Epicenter: The point on Earth’s surface directly above the focus

Body waves: Waves that travel from the focus of an earthquake through Earth

P waves: Primary/compressional waves that squeeze and stretch rock material as they pass through Earth. P waves can travel through any material – solid rock, magma, ocean water, even air

S waves: Shear waves/secondary waves cause particles of rock to material to move at right angles to the direction in which the waves are traveling. S waves can travel through solid material but not liquids or gases

Surface waves: Earthquake waves that travel along Earth’s surface. Love Waves and Rayleigh waves are two types of surface waves

Key Idea: Most earthquakes result from the release of stress that has built up at plate boundaries.

|Stress builds at faults |

|↓ |

|Plates shift/earthquake occurs |

|↓ |

|Body Waves |Surface Waves |

|↓ ↓ |↓ ↓ |

|S waves |P waves |Love waves |Rayleigh Waves |

S waves and Love waves are the waves that cause particles of materials to move at right angles to the direction of the waves.



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10.2- Locating and Measuring Earthquakes

Vocabulary:

Seismograph: An instrument that detects and records waves produced by earthquakes

Seismogram: The recording of an earthquake made by a seismograph

Magnitude: The measure of the amount of energy released in an earthquake

Key Idea: A seismograph is used to determine the magnitude of an earthquake and the location of the epicenter.

|Sesimograph |Things both have in common |Seismogram |

|The instrument consists of weight, pen, and|Both the seismograph and the seismogram are|The record sheet, indicates arrival time of|

|drum |used to detect earthquakes |each type of wave |

Why do we need seismograms from several locations in order to locate an earthquake’s epicenter?

A seismogram indicates only the distance from a station to the epicenter; therefore, the epicenter could be any point on a circle with that distance as a radius. By picking three (3) or more stations, and drawing a circle around each, scientists can locate the epicenter at the point where the three circles meet.

[pic]The time at

which a seismic wave arrives at a seismometer. The image to the right shows a seismogram with the P wave and S wave arrival times marked. According to this example, the P wave arrived at the recording device shortly after 11:43 AM and the S wave arrived shortly before 11:45 AM.

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10.3 – Earthquake Hazards

Vocabulary:

Liquefaction: A temporary state in which loose soil and rock materials take on the property of liquid, often as the result of severe ground shaking.

Aftershock: A smaller earthquake that follows a larger earthquake

Tsunami: A large ocean wave that results from an underwater earthquake, landslide, or volcanic eruption

Seismic gap: An area along a seismically active fault where no earthquake activity has occurred over a long period of time.

Key Idea: The amount of damage an earthquake causes depends on its magnitude and where it occurs. Safe building practices can limit loss of life and damage to property.

|1.Type of earthquake damage |2. Preventing earthquake damage |

|Liquefaction more common on bogs and soft landfill |determining what factors make structures resist earthquake damage|

|Liquefaction can lead to foundation failure |revising building codes as in Japan |

|There can be up to 1000 aftershocks a day after a major | |

|earthquake | |

|Aftershocks can lead to ruptured gas lines and fires | |

|Tsunamis can cause massive destruction | |

|3. Areas of earthquake risk |4. Predicting earthquakes |

|regions lying at plate boundaries, such as California, Alaska. |predicting when, where, and what magnitude. |

|Places where many faults are buried beneath rock, such as New |Plotting earthquake activity along faults |

|Madrid, Mississippi |Identifying seismic gaps |

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Animation of tsunami caused by earthquake

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10.4 – Studying Earth’s Interior

Key Idea: Scientists use data from seismic waves to learn about the structure of Earth’s interior.

Difference between S waves and P waves:

S waves cannot travel through liquid Since S waves cannot pass through the outer core, scientists believe that the outer core is liquid.

P waves can travel through any matter which includes: solid rock, magma, ocean water, even air.

Shadow Zone:

This is the area where P waves are refracted and S waves cannot pass through the liquid outer core.

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University of Colorado / AP

A scientist studies the New Madrid seismic zone in Lake County, Tenn., in this undated photo. A new study of the area found that the faults in the zone have moved much less than expected -- a sign that the area may not generate any more earthquakes.

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