What Are Earthquakes

What Are Earthquakes

Science Chapter 7 Section 1 Notes

Science Chapter 7 Section 1 Notes

Section VocabularySection Vocabulary Earthquake: a movement or trembling of the

ground that is caused by a sudden release of energy when rocks along a fault move.

Elastic Rebound: the sudden return of elastically deformed rock to its undeformed shape

Seismic Wave: a wave of energy that travels through the Earth and away from an earthquake in all directions.

Earthquake: a movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move.

Elastic Rebound: the sudden return of elastically deformed rock to its undeformed shape

Seismic Wave: a wave of energy that travels through the Earth and away from an earthquake in all directions.

I. Where Earthquakes Happen

I. Where Earthquakes Happen

a) Most are near the boundaries of tectonic plates.

b) Large earthquakes have occurred in the middle of the North American plate.

c) Tectonic plates move in different directions and speeds.

d) Can push or pull away from one another.

a) Most are near the boundaries of tectonic plates.

b) Large earthquakes have occurred in the middle of the North American plate.

c) Tectonic plates move in different directions and speeds.

d) Can push or pull away from one another.

I. Where Earthquakes Happen

I. Where Earthquakes Happen

e. They can skip slowly past one another horizontally.

f. Movements break crust into a series of faults.

g. A fault is a break in Earth’s crust along which blocks of rock slide relative to one another.

e. They can skip slowly past one another horizontally.

f. Movements break crust into a series of faults.

g. A fault is a break in Earth’s crust along which blocks of rock slide relative to one another.

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Map of Earthquakes

II. Faults at Tectonic Plates

II. Faults at Tectonic Plates

A. Earthquakes at Divergent Boundariesa. Two tectonic plates pull away from one another.b. Plates cause lithosphere to break into blocks and blocks drop down relative to others.c. Example: Mid-Ocean Ridge. Lithosphere is thin and weak. Because lithosphere is thin, earthquakes along the faults are shallow.

A. Earthquakes at Divergent Boundariesa. Two tectonic plates pull away from one another.b. Plates cause lithosphere to break into blocks and blocks drop down relative to others.c. Example: Mid-Ocean Ridge. Lithosphere is thin and weak. Because lithosphere is thin, earthquakes along the faults are shallow.

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II. Faults at Tectonic Plates

II. Faults at Tectonic Plates

B. Earthquakes at Convergent Boundaries

a. Two tectonic plates collide with one another.

b. 2 Things may happen:

a. i. Both plates may crumple up to form mountains.

b. ii. One plate may move underneath and sink into the mantle. This is called subduction.

c. During subduction or mountain building the rocks are compressed and this breaks them into fault blocks. These create reverse faults.

B. Earthquakes at Convergent Boundaries

a. Two tectonic plates collide with one another.

b. 2 Things may happen:

a. i. Both plates may crumple up to form mountains.

b. ii. One plate may move underneath and sink into the mantle. This is called subduction.

c. During subduction or mountain building the rocks are compressed and this breaks them into fault blocks. These create reverse faults.

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II. Faults at Tectonic Plates

II. Faults at Tectonic Plates

C. Earthquakes at Transform Boundariesa. Two plates move past one another

horizontally (or in opposite directions).b. Rocks on both sides are sheared (broken

as they grind past).c. The blocks form a series of strike-slip

faults as blocks move.d. Most exist between plates made of oceanic

lithosphere

C. Earthquakes at Transform Boundariesa. Two plates move past one another

horizontally (or in opposite directions).b. Rocks on both sides are sheared (broken

as they grind past).c. The blocks form a series of strike-slip

faults as blocks move.d. Most exist between plates made of oceanic

lithosphere

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II. Faults at Tectonic Plates

II. Faults at Tectonic Plates

D. Fault Zones– Places along plate boundaries where

interconnected faults are located.– Have different lengths.– Occur at different depths.– Cut through the lithosphere in different

directions.a. Normal, Reverse, and Strike-Slip, faults can all

occur in one single fault zone.b. The San Andreas fault zone in California is an

example.

D. Fault Zones– Places along plate boundaries where

interconnected faults are located.– Have different lengths.– Occur at different depths.– Cut through the lithosphere in different

directions.a. Normal, Reverse, and Strike-Slip, faults can all

occur in one single fault zone.b. The San Andreas fault zone in California is an

example.

III. Why Earthquakes Happen

III. Why Earthquakes Happen

a. As plates move, stress near the edges increases and rock deforms.

b. Rock deforms mainly 2 ways:i. Plastic Deformation- fold and deform

like clay being molded. ii. Elastic Deformation-rocks are

stretched like a rubber band. This is when energy is released (earthquake).

a. As plates move, stress near the edges increases and rock deforms.

b. Rock deforms mainly 2 ways:i. Plastic Deformation- fold and deform

like clay being molded. ii. Elastic Deformation-rocks are

stretched like a rubber band. This is when energy is released (earthquake).

III. Why Earthquakes Happen

III. Why Earthquakes Happen

A. Elastic Rebounda. The sudden return of deformed rock to

original shape.b. Happens when stress on rock becomes

so great the rock breaks or fails.c. During sudden motion, energy is

released and travels through rock in form of seismic waves.

A. Elastic Rebounda. The sudden return of deformed rock to

original shape.b. Happens when stress on rock becomes

so great the rock breaks or fails.c. During sudden motion, energy is

released and travels through rock in form of seismic waves.

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IV. Earthquake WavesIV. Earthquake Waves

A. P Waves

a. P waves are Pressure or Primary Waves

A. The fastest seismic waves.

B. They are the first ones detected.

C. Can travel through solids, liquids and gases.

A. P Waves

a. P waves are Pressure or Primary Waves

A. The fastest seismic waves.

B. They are the first ones detected.

C. Can travel through solids, liquids and gases.

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IV. Earthquake WavesIV. Earthquake Waves

B. S Wavesa. S waves are shear waves.b. Second- fastest seismic waves.c. Shear rock side to side.d. Cannot travel through parts that are

completely liquid.e. Another name is secondary waves.

B. S Wavesa. S waves are shear waves.b. Second- fastest seismic waves.c. Shear rock side to side.d. Cannot travel through parts that are

completely liquid.e. Another name is secondary waves.

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IV. Earthquake WavesIV. Earthquake Waves

C. Surface Wavesa. Move only along Earth’s surface.b. Produce motion only near the top of

the Earth’s crust.c. Tend to cause most damage.d. 2 types:

i. a rolling up-and-down motion.ii. Back-and-forth motion.

C. Surface Wavesa. Move only along Earth’s surface.b. Produce motion only near the top of

the Earth’s crust.c. Tend to cause most damage.d. 2 types:

i. a rolling up-and-down motion.ii. Back-and-forth motion.

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