essential knowledge: what are the causes of earthquakes?

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• Essential Knowledge: • What are the causes of earthquakes?

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Seismology-study of earthquakes.

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Page 1: Essential Knowledge: What are the causes of earthquakes?

• Essential Knowledge:• What are the causes of earthquakes?

Page 2: Essential Knowledge: What are the causes of earthquakes?

UNIT 7 (1) PLATE TECTONICS, EARTHQUAKES AND VALCANOES

Earthquake is series of seismic waves or tremors in the earth’s crust. Caused when pressure builds up at edge of plates as they collide or slide past one another.Pressure released a huge amount of energy is released causing the plates to shake.

Page 3: Essential Knowledge: What are the causes of earthquakes?

Seismology-study of earthquakes.

Page 4: Essential Knowledge: What are the causes of earthquakes?

• Earthquake vocabulary:• Tremors-waver of seismic energy which spread

from the focus.• Aftershocks- smaller tremors which may occur

hours or days after original earthquakes. They can be extremely dangerous because they

may cause already damaged building to collapse.

Page 5: Essential Knowledge: What are the causes of earthquakes?

• Focus- (Hypocenter)place deep in the earth’s crust where earthquake begins.

• Epicenter- place on surface of earth, directly above focus. The tremors are strongest at this point.

Page 6: Essential Knowledge: What are the causes of earthquakes?
Page 7: Essential Knowledge: What are the causes of earthquakes?

• Elastic Rebound-rocks bend until the strength of the rock is exceeded.

• Rupture occurs& rocks quicklyrebound to an Undeformed shape.Energy is releasedin waves radiateoutward from fault.

Page 8: Essential Knowledge: What are the causes of earthquakes?

• Richter scale-used to describe strength of earthquake.

• Seismograph-device that measures strength of earthquake.

Page 9: Essential Knowledge: What are the causes of earthquakes?

• Richter scale is logarithmic (6 is 10X stronger than 5).

Page 10: Essential Knowledge: What are the causes of earthquakes?

Magnitude and Energy

5. Magnitude and Intensity

Magnitude Energy Explosive Power Example

3 One ton of Explosives World Trade Center Collapse

2

1 Topple 50-meter tree

One kilogram of explosives

Head-on colision at 60 mph

0 Drop a car 10 meters

Half stick of dynamite Very bad day skydiving

-1 Impact of bullet One gram of explosives

-2 Hammer blow

-3 Dribbling a basketball

Page 11: Essential Knowledge: What are the causes of earthquakes?

Magnitude and Energy

5. Magnitude and Intensity

Magnitude Energy Explosive Power Example

9 U.S. Energy Use for a month

Alaska 1964Indonesia 2004

8 U.S. Energy Use for a day

San Francisco, 1906

7 One Megaton World Series Earthquake, 1989

6 U.S. Energy Use for a minute

Large Thunderstorm

5 One Kiloton

4

3 One ton of explosives World Trade Center Collapse

Page 12: Essential Knowledge: What are the causes of earthquakes?

Seismic waves-response of material to arrival of energy fronts released by rupture. 2 types body waves P and S Surface waves R and L

Page 13: Essential Knowledge: What are the causes of earthquakes?

Body Waves: P and S waves• Body waves

– P or primary waves• fastest waves• travel through solids,

liquids, or gases• compressional wave,

material movement is in same direction as wave movement

– S or secondary waves• slower than P waves• travel through solids

only• shear waves - move

material perpendicular to wave movement

Page 14: Essential Knowledge: What are the causes of earthquakes?

Surface Waves: R and L waves

• Surface Waves– Travel just below or along the ground’s surface– Slower than body waves; rolling and side-to-side

movement– Especially damaging to buildings

Page 15: Essential Knowledge: What are the causes of earthquakes?

How is an Earthquake’s Epicenter Located? Seismic wave behavior

– P waves arrive first, then S waves, then L and R– Average speeds for all these waves is known– After an earthquake, the difference in arrival times at a seismograph

station can be used to calculate the distance from seismograph to the epicenter.

Page 16: Essential Knowledge: What are the causes of earthquakes?
Page 17: Essential Knowledge: What are the causes of earthquakes?

How is an Earthquake’s Epicenter Located?Time-distance graph

showing average travel times for P- and S-waves. Farther away a seismograph is from e focus of an earthquake, longer interval between arrivals of the P- and S- waves

Page 18: Essential Knowledge: What are the causes of earthquakes?

How is an Earthquake’s Epicenter Located?

• Three seismograph stations are needed to locate epicenter of an earthquake

• A circle where radius equals distance to epicenter is drawn

• Intersection of circles locates epicenter

Page 19: Essential Knowledge: What are the causes of earthquakes?

• Modified Mercalli Intensity Map– 1994 Northridge, CA earthquake, magnitude

6.7

• Intensity– subjective

measure of kind of damage done & people’s reactions to it

– isoseismal lines identify areas of equal intensity

Page 20: Essential Knowledge: What are the causes of earthquakes?

How are the Size and Strength of an Earthquake Measured?

• Magnitude– Richter scale

measures total amount of energy released by an earthquake; independent of intensity

– Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open-ended logarithmic scale

Page 21: Essential Knowledge: What are the causes of earthquakes?

ESSENTIAL KNOWLEDGE:What are the factors contributing to earthquake damage, and other dangers associated with earthquakes.

Page 22: Essential Knowledge: What are the causes of earthquakes?

Can Earthquakes be Controlled?

• Graph showing the relationship between the amount of waste injected into wells per month and the average number of Denver earthquakes per month

• Some have suggested that pumping fluids into seismic gaps will cause small earthquakes while preventing large ones

Page 23: Essential Knowledge: What are the causes of earthquakes?

Faults- fracture along which blocks of crust on either side have moved relative to one another parallel to the fracture. Strike-slip-vertical fractures where blocks have mostly moved horizontally. Faults are classified bykinds of movement thatoccurs along them.Strike-slip left lateralfault.

Page 24: Essential Knowledge: What are the causes of earthquakes?

• Strike-slip right lateral fault.

Page 25: Essential Knowledge: What are the causes of earthquakes?

• Dip-slip faults-inclined fractures where blocks have shifted vertically

• Dip-slip normal fault. Rock mass above an inclined fault

moves down.

Page 26: Essential Knowledge: What are the causes of earthquakes?

• Dip-slip reverse fault. Rock above fault moves up.

Page 27: Essential Knowledge: What are the causes of earthquakes?

• Normal faults are caused by extension.• Reverse faults are caused by compression. • Reverse faults are often called thrust faults.

Page 28: Essential Knowledge: What are the causes of earthquakes?
Page 29: Essential Knowledge: What are the causes of earthquakes?

• Earthquake Hazards.• Building collapse

• Landslides

Page 30: Essential Knowledge: What are the causes of earthquakes?

• Fire

• Tsunamis

Page 31: Essential Knowledge: What are the causes of earthquakes?

• Most dangerous buildings adobe house• Unreinforced masonry.• Reinforces concrete.• Steel-frame.• Small wood-frame house.

Page 32: Essential Knowledge: What are the causes of earthquakes?

• Tsunamis usually caused by submarine landslides-travel 400mph

• They pass unnoticed at sea, but cause damage on shore.

• There is a warning network around Pacific ocean, then can forecast arrival.

• Damage from a Tsunamis depends on direction of travel of wave, harbor shape, bottom, and tide & weather.

Page 33: Essential Knowledge: What are the causes of earthquakes?
Page 34: Essential Knowledge: What are the causes of earthquakes?

5. Magnitude and Intensity

Page 35: Essential Knowledge: What are the causes of earthquakes?

Earthquake Fatalities Since 1800

7. Predicting earthquakes is not yet possible

Page 36: Essential Knowledge: What are the causes of earthquakes?

Are Earthquakes Getting More Frequent?

7. Predicting earthquakes is not yet possible

Page 37: Essential Knowledge: What are the causes of earthquakes?

Some Important Earthquakes

1755 - Lisbon, Portugal • Killed 70,000, Raised Waves in Lakes all over

Europe • First Scientifically Studied Earthquake 1811-1812 - New Madrid, Missouri • Felt over 2/3 of the U.S. • Few Casualties 1886 - Charleston, South Carolina • Felt All over East Coast, Killed Several Hundred. • First Widely-known U.S. Earthquake

Page 38: Essential Knowledge: What are the causes of earthquakes?

Some Important Earthquakes 1906 - San Francisco • Killed 500 (later studies, possibly 2,500) • First Revealed Importance of Faults 1923 – Tokyo - Killed 140,000 in firestorm1964 - Alaska • Killed about 200 • Wrecked Anchorage. • Tsunamis on West Coast. 1976 - Tangshan, China • Hit an Urban Area of Ten Million People • Killed 650,000

Page 39: Essential Knowledge: What are the causes of earthquakes?

• History and earthquakes• In last 500 years more then 7 million people

have died.• Destroyed economies and food sources.

Page 40: Essential Knowledge: What are the causes of earthquakes?

• Lisbon Earthquake 1755 -60,000 killed –ocean waves 30-40 feet above high tide level swamped city –fires burned 3 days.

Page 41: Essential Knowledge: What are the causes of earthquakes?