F orces within earth
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Transcript of F orces within earth
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FORCES WITHIN EARTH
Chapter 19.1 EARTHQUAKES
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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
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Types of Stress Tension- pull Compression-
push Shear- twist
Strain- deformation caused by stress
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Ductile Deformation Elastic deformation
occurs as a result of low stress
Ductile deformation occurs when stress is high
When does fracture occur?
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Faults Fractures in the Earth’s crust along
which movement occurs
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Types of Faults Normal- tension Reverse- compression Strike-slip- shear
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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
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Focus- point where an earthquake originates Epicenter- point on surface directly above the
focus
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SEISMIC WAVES & EARTHS INTERIOR
Chapter 19.2 EARTHQUAKES
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Seismology Study of earthquake waves Seismograph/seismometer- register the vibrations Seismogram- the record of vibrations
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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?
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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
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MEASURING & LOCATING
EARTHQUAKES
Chapter 19.3 EARTHQUAKES
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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
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Moment Magnitude Scale Most used today Based on the
size of the fault rupture, amount of movement along the fault, and the rocks’ stiffness
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Modified Mercalli Scale Based on the
amount of damage done to structures
Measure of intensity
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Intensity Relates to Magnitude
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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?
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Seismic Belts 80% occur in the Circum-Pacific Belt 15% occur in the Mediterranean-Asian Belt
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EARTHQUAKES & SOCIETY
Chapter 19.4 EARTHQUAKES
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Earthquake Hazards Structural Failure
PancakingCollapse
1999 Izmit earthquake in Turkey2010 Pichilemu earthquake in Chile
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Earthquake Hazards Land and Soil Failure
LiquifactionSeismic wave amplification
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Liquifaction in Christchurch, NZ
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Earthquake Hazards Fault Scarps
Vertical offset
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Earthquake Hazards Tsunamis
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Seismic Risk
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Earthquake Prediction History Strain
Accumulation