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Chapter 19.1 EARTHQUAKES. F orces within earth. Earthquakes. Natural vibrations of the ground caused by movement along fractures in the crust or volcanic eruptions Fractures form when stress exceeds the strength of the rock. Types of Stress. Tension- pull Compression- push Shear- twist

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F orces within earth

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Chapter 19 1 earthquakes

Chapter 19.1 EARTHQUAKES

Forces within earth



  • Natural vibrations of the ground caused by movement along fractures in the crust or volcanic eruptions

  • Fractures form when stress exceeds the strength of the rock

Types of stress

Types of Stress

  • Tension- pull

  • Compression- push

  • Shear- twist

  • Strain- deformation caused by stress

Ductile deformation

Ductile Deformation

  • Elastic deformation occurs as a result of low stress

  • Ductile deformation occurs when stress is high

  • When does fracture occur?



  • Fractures in the Earth’s crust along which movement occurs

Types of faults

Types of Faults

  • Normal- tension

  • Reverse- compression

  • Strike-slip- shear

Seismic waves

Seismic Waves

  • (Primary) P-waves- squeeze and pull rocks in the same direction of the waves

  • (Secondary) S-waves- cause rock to move at right angles to the direction of the waves

  • Surface waves- cause rock to move up & down

F orces within earth

  • Focus- point where an earthquake originates

  • Epicenter- point on surface directly above the focus

Chapter 19 2 earthquakes

Chapter 19.2 EARTHQUAKES

Seismic waves & earths interior



  • Study of earthquake waves

  • Seismograph/seismometer- register the vibrations

  • Seismogram- the record of vibrations

Travel time

Travel- time

  • Travel time for P and S waves differ

  • Can you tell which ones reach a location first?

  • Where is the biggest difference in the time one wave arrives before the other?

Clues to earth s interior

Clues to Earth’s Interior

  • P waves are refracted in the core

  • S waves can not travel through liquids

  • Behavior of waves provide details of Earth’s interior structure and composition

Chapter 19 3 earthquakes

Chapter 19.3 EARTHQUAKES

Measuring & locating earthquakes

Earthquake magnitude and intensity

Earthquake Magnitude and Intensity

  • Magnitude- the amount of energy released during an earthquake

  • Richter scale- earthquake rating based on the size of the largest seismic waves

  • Increases by power of 10 for each magnitude

Moment magnitude scale

Moment Magnitude Scale

  • Most used today

  • Based on the size of the fault rupture, amount of movement along the fault, and the rocks’ stiffness

Modified mercalli scale

Modified Mercalli Scale

  • Based on the amount of damage done to structures

  • Measure of intensity

Intensity relates to magnitude

Intensity Relates to Magnitude

Locating an earthquake

Locating an Earthquake

  • Distance from epicenter is calculated by comparing the separation time between P and S waves

  • 3 locations are needed to accurately determine the epicenter of the earthquake

  • Why?

Seismic belts

Seismic Belts

  • 80% occur in the Circum-Pacific Belt

  • 15% occur in the Mediterranean-Asian Belt

Chapter 19 4 earthquakes

Chapter 19.4 EARTHQUAKES

Earthquakes & Society

Earthquake hazards

Earthquake Hazards

  • Structural Failure

    • Pancaking

    • Collapse

2010 Pichilemu earthquake in Chile

1999 Izmit earthquake in Turkey

Earthquake hazards1

Earthquake Hazards

  • Land and Soil Failure

    • Liquifaction

    • Seismic wave amplification

Liquifaction in christchurch nz

Liquifaction in Christchurch, NZ

Earthquake hazards2

Earthquake Hazards

  • Fault Scarps

    • Vertical offset

Earthquake hazards3

Earthquake Hazards

  • Tsunamis

Seismic risk

Seismic Risk

Earthquake prediction

Earthquake Prediction

  • History

  • Strain Accumulation

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