1. What are Earthquakes? The shaking or trembling caused by the sudden release of energy Usually...

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

o The actual place underground where the rocks break producing vibrations is called the focus

o The place on the surface directly above the focus is called the epicenter

2. Earthquake Anatomy

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

3. What causes Earthquakes?

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

A. Extension ForceA. Extension Force: stretching or pulling force Makes a normal fault

4. What types of 4. What types of forces forces are created?

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

B. Compression ForceB. Compression Force: force pushing something

togethertogether Makes a reverse fault

4. What types of 4. What types of forcesforces are created?

C. Shear ForceC. Shear Force: a system of forces

that operates against a body from different sides

Makes a strike-slip fault

4. What types of 4. What types of forcesforces are created?

Landscape Shifting, Wallace Creek

Source: John S. Shelton

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

B. Richter ScaleB. 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

6. How do we Measure Earthquakes?

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

Map of Epicenter, KY, TN

8. Earthquake Dangers

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

San Francisco, 1906

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

Generation of a Tsunami

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.

C. 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

Source: Steve McCutcheon/Alaska Pictorial Services

Elevated Freeway Collapse in Kobe

Source: Hosaka Naoto/Gamma Liaison

D. 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

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