Earthquakes

1. What are Earthquakes? The shaking or trembling caused by the sudden release of energy Usually associated with faulting or breaking of rocks

Where Do Earthquakes Occur and How Often? ~80% of all earthquakes occur in the circum-Pacific belt most of these result from convergent margin activity ~15% occur in the Mediterranean-Asiatic belt remaining 5% occur in the interiors of plates and on spreading ridge centers more than 150,000 quakes strong enough to be felt are recorded each year

2. Earthquake Anatomy The actual place underground where the rocks break producing vibrations is called the focus The place on the surface directly above the focus is called the epicenter

3. What causes Earthquakes? A. Movement along faults: occurs when the energy exceeds the friction holding the sides of the fault together and is suddenly released. This is the Elastic Rebound Theory. B. Movement of magma (volcanic) C. Volcanic eruptions

What is the Elastic Rebound Theory? Explains how energy is stored in rocks Rocks bend until the strength of the rock is exceeded Rupture occurs and the rocks quickly rebound to an undeformed shape Energy is released in waves that radiate outward from the fault

4. What types of forces are created? A. Extension Force: stretching or pulling force Makes a normal fault

Normal Fault http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en

4. What types of forces are created? B. Compression Force: force pushing something together Makes a reverse fault

Reverse Fault http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en

4. What types of forces are created? C. Shear Force: a system of forces that operates against a body from different sides Makes a strike-slip fault

Strike-Slip Fault http://www.geo.uib.no/jordskjelv/index.php?topic=earthquakes&lang=en

Landscape Shifting, Wallace Creek Source: John S. Shelton Copyright © Houghton Mifflin Company. All rights reserved.

5. Seismic Waves Originate at the focus and travel outward in all directions Foreshocks: small earthquakes that come before a major earthquake Aftershocks: Are adjustments in the crust after an earthquake

6. How do we Measure Earthquakes? A. Earthquake waves are recorded by a seismograph and the recording of waves on paper is called seismogram

6. How do we Measure Earthquakes? B. Richter Scale: Measures the amplitude of earthquake waves on seismograms Scale from 1-10 Each number is 10 times the amplitude of the number below

7. Locating Earthquakes After an earthquake, the difference in arrival times of seismic waves at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.

7. Locating Earthquakes Copyright © Houghton Mifflin Company. All rights reserved.

Map of Epicenter, KY, TN Copyright © Houghton Mifflin Company. All rights reserved.

8. Earthquake Dangers A. Most injuries and deaths are caused by falling objects and most property damage results from fires that start

San Francisco, 1906

San Francisco, 1906

8. Earthquake Dangers B. Tsunami: seismic sea wave sometimes generated when an earthquake originates on the ocean floor

Generation of a Tsunami Copyright © Houghton Mifflin Company. All rights reserved.

Tsunami—December 2004 http://www.bedford.k12.ny.us:16080/flhs/science/images/tsunami2004/

NSF North Mississippi GK-8 Who Feels the Shaking? The shaking starts at the epicenter and spreads in circles outward much like the ripples of water dripping into a puddle. NSF North Mississippi GK-8

8. Earthquake Dangers C. Liquefaction: unconsolidated materials that are water saturated may turn to a fluid causing some underground objects such as storage tanks to float to the surface Ground fissures caused by liquefaction near the mouth of the Pajaro River in California during the 1989 Loma Prieta earthquake. When the surface of the ground oscillates, wet, sandy, and muddy soils can flow like a liquid. This is liquefaction. You can liquefy wet sand at the beach by pumping it up and down with your feet. Photo courtesy of the Loma Prieta Collection, Earthquake Engineering Research Center, UC Berkeley.

Liquefaction Copyright © Houghton Mifflin Company. All rights reserved.

Source: Steve McCutcheon/Alaska Pictorial Services Liquefaction Source: Steve McCutcheon/Alaska Pictorial Services Copyright © Houghton Mifflin Company. All rights reserved.

Elevated Freeway Collapse in Kobe Source: Hosaka Naoto/Gamma Liaison Copyright © Houghton Mifflin Company. All rights reserved.

8. Earthquake Dangers D. Landslides

Earthquake Safety Protect yourself from falling objects (GET UNDER SOMETHING) or stand in a hallway or doorway (watch out for a swinging door) Do not try to go outside during the earthquake After the earthquake and before the aftershocks, go outside Do not return to the building until it has been inspected