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Earthquakes. Earth Science chapters 5 and 6. Earth’s interior. Crust – thin layer of solid rock including dry land and ocean floor Mantle – rock that is very hot, but solid Outer core – liquid metal Movements may cause magnetic field Inner core – dense, solid metal. Wegener’s hypothesis.

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earthquakes

Earthquakes

Earth Science chapters 5 and 6

Earth Science Chapters 5 and 6

earth s interior
Earth’s interior
  • Crust – thin layer of solid rock including dry land and ocean floor
  • Mantle – rock that is very hot, but solid
  • Outer core – liquid metal
    • Movements may cause magnetic field
  • Inner core – dense, solid metal

Earth Science Chapters 5 and 6

wegener s hypothesis
Wegener’s hypothesis
  • 1910
  • All continents were once joined together in a single landmass and have since drifted apart
  • Pangea – supercontinent
    • About 300 million years ago
    • When reptiles and winged insects first appeared
  • Later broke apart and drifted

Earth Science Chapters 5 and 6

wegener s proof p 138 139
Wegener’s proof – p. 138 - 139
  • Land features
    • Mountain ranges and coal fields line up
  • Fossils
    • Plant fossils found on widely separated landmasses
    • Freshwater reptile fossils found in places now separated by oceans
  • Climate
    • Evidence that continents that are now cold were once tropical, and vice versa

Earth Science Chapters 5 and 6

rejection
Rejection
  • Wegener’s hypothesis was rejected in his time.
  • He was unable to explain how continents moved.
  • He challenged the theories of mountain formation at the time.
  • Later evidence supported his theory.

Earth Science Chapters 5 and 6

plate tectonics
Plate tectonics
  • Explains the formation, movement, and subduction of Earth’s plates
  • Movement caused by motion in the mantle
  • Plates collide, pull apart, or grind past each other
    • Changes Earth’s surface

Earth Science Chapters 5 and 6

divergent boundaries
Divergent boundaries
  • Where two plates move apart
  • Creates mid-ocean ridges and rift valleys

Earth Science Chapters 5 and 6

convergent boundaries
Convergent boundaries
  • Where two plates come together
  • Plates collide
  • One plate is subducted beneath the other
    • Forms mountains or ocean trenches

Earth Science Chapters 5 and 6

transform boundaries
Transform boundaries
  • Where two plates slip past each other moving in opposite directions
  • Often causes earthquakes

Earth Science Chapters 5 and 6

discuss
Discuss
  • Describe Earth’s interior.
  • Describe the three different types of plate boundaries.

Earth Science Chapters 5 and 6

stress
Stress
  • Force that acts on a rock to change its shape or volume
  • Many rocks can bend or fold, but they eventually break

Earth Science Chapters 5 and 6

tension
Tension
  • Stretches rock by pulling on crust
  • Rock gets thinner in the middle
  • Happens when two plates move apart
    • Divergent boundaries

Earth Science Chapters 5 and 6

compression
Compression
  • Squeezes rock until it folds or breaks
  • Happens when two plates come together
    • Convergent boundaries

Earth Science Chapters 5 and 6

shearing
Shearing
  • Pushes rock in two opposite directions
  • Can cause rock to break apart or change its shape
  • Happens at transform boundaries

Earth Science Chapters 5 and 6

fault
Fault
  • Break in rock where surfaces slip past each other
  • Mostly along plate boundaries

Earth Science Chapters 5 and 6

normal fault p 164
Normal fault p. 164
  • Fault at an angle
  • One block of rock is below the fault
    • Footwall
  • One block of rock is above fault
    • Hanging wall
  • Hanging wall slips downward
    • Falls downhill
  • Where plates diverge
  • Forms valleys

Earth Science Chapters 5 and 6

reverse fault p 165
Reverse fault p. 165
  • Where plates converge
  • Same structure as normal fault, but opposite motion
  • Hanging wall slides up
    • Moves uphill
  • Forms mountains

Earth Science Chapters 5 and 6

strike slip fault p 165
Strike-slip fault p. 165
  • At transform boundaries
  • Plates slip sideways with little or no vertical motion
  • Often causes earthquakes

Earth Science Chapters 5 and 6

folded crust
Folded crust
  • Wrinkles
  • Makes mountains
  • Anticline
    • Fold that bends upward (mountain)
  • Syncline
    • Fold that bends downward (valley)

Earth Science Chapters 5 and 6

plateau
Plateau
  • Large area of flat elevated land
  • Can be formed by forces lifting Earth’s crust

Earth Science Chapters 5 and 6

discuss1
Discuss
  • What are the three main types of stress in rock?
  • Compare and contrast the way that compression affects the crust to the way that tension affects the crust.

Earth Science Chapters 5 and 6

earthquake
Earthquake
  • The shaking and trembling that results from the movement of rock beneath Earth’s surface
  • Often too small to notice
  • Releases a lot of stored energy in a few seconds

Earth Science Chapters 5 and 6

focus
Focus
  • Where the rock beneath the surface that is under stress breaks

Earth Science Chapters 5 and 6

epicenter
Epicenter
  • On surface directly above the focus

Earth Science Chapters 5 and 6

seismic waves
Seismic waves
  • Carry energy away from the focus
    • Through Earth’s interior
    • Along Earth’s surface

Earth Science Chapters 5 and 6

p waves
P waves
  • Primary waves
  • Arrive first (travel fastest)
  • Compressional or longitudinal waves
  • Can damage buildings

Earth Science Chapters 5 and 6

s waves
S waves
  • Secondary waves
  • Arrive second
  • Transverse waves
  • Vibrate up and down and side to side
  • Shake ground back and forth
  • Shake structures violently
  • Cannot travel through liquid

Earth Science Chapters 5 and 6

surface waves
Surface waves
  • May occur when P and/or S wave reach the surface
  • Move the slowest
  • Can be the most destructive
  • Can make the ground roll like ocean waves
  • Can shake buildings side to side

Earth Science Chapters 5 and 6

mercalli scale
Mercalli scale
  • Rates earthquakes according to level of damage at a given place
  • Numbered from I to XII
  • See page 173

Earth Science Chapters 5 and 6

richter scale
Richter scale
  • Rates earthquake’s magnitude (size)
  • Based on seismograph readings of seismic waves
  • Accurate for small, nearby earthquakes
  • Less accurate for large or distant earthquakes

Earth Science Chapters 5 and 6

moment magnitude scale
Moment magnitude scale
  • Estimates the total energy released by an earthquake
  • Can be used on any earthquake
  • Based on info from seismographs
  • On the news when they say Richter scale, it usually is really the moment magnitude scale

Earth Science Chapters 5 and 6

magnitudes
Magnitudes
  • Each one-point increase in magnitude represents the release of about 32 times more energy.
    • A magnitude 5 quake releases 32 times as much energy as a magnitude 4, about 1024 times as much as a magnitude 3, about 32768 times as much as a magnitude 2, and about 1048576 times as much as a magnitude 1

Earth Science Chapters 5 and 6

magnitudes1
Magnitudes
  • Below magnitude 3 is rarely noticed by people
  • Below 5 are small and cause little damage
  • Between 5 and 6 cause moderate damage
  • Above 6 cause great damage
  • Above 8 are extremely rare
  • During 1900s only two quakes above 9
    • Chile in 1960
    • Alaska in 1964

Earth Science Chapters 5 and 6

chile 1960
Chile 1960
  • Magnitude 9.5
  • Highest recorded

Earth Science Chapters 5 and 6

alaska 1964
Alaska 1964
  • 2nd highest
  • 9.2

Earth Science Chapters 5 and 6

locating epicenter
Locating epicenter
  • Measure difference in arrival times of P waves and S waves
  • Use data from at least three stations
  • Draw circles out from each station
  • Epicenter is where circles cross

Earth Science Chapters 5 and 6

discuss2
Discuss
  • What kind of movement is produces by each of the three types of seismic waves?
  • In what order to seismic waves arrive?
  • What is an earthquake’s magnitude?

Earth Science Chapters 5 and 6

seismograph
Seismograph
  • Rotating drum moves with vibrations
    • Attached to ground
  • Weighted pen does not
    • Weight resists motion
  • Modern seismographs use electronic sensors instead of pens

Earth Science Chapters 5 and 6

seismogram
Seismogram
  • Record of seismic waves produced by seismograph
    • P waves first
    • S waves next
    • Surface waves largest spikes

Earth Science Chapters 5 and 6

monitoring faults
Monitoring faults
  • Check for slight rise or fall in elevation or tilt of land
  • Helps predict earthquakes

Earth Science Chapters 5 and 6

tiltmeter
Tiltmeter
  • Measures tilting or raising of ground
  • Like levels
  • Contain two liquid-filled bulbs connected by a stem
  • Liquid level in each is monitored

Earth Science Chapters 5 and 6

creep meter
Creep meter
  • Measures horizontal movement of ground
  • Uses wire stretched across a fault
    • One end attached to post
    • Other end attached to a weight that can slide
    • Amount of sliding measured

Earth Science Chapters 5 and 6

laser ranging device
Laser-ranging device
  • Detects horizontal movements
  • Times a laser beam as it travels to a reflector and back
  • If the time changes, that means the reflector has moved

Earth Science Chapters 5 and 6

gps satellite
GPS satellite
  • Measures change in elevation and horizontal movement
  • Measures tiny movements in markers set up on either side of a fault

Earth Science Chapters 5 and 6

finding faults
Finding faults
  • Often hidden beneath rock
  • Seismic waves reflected off faults
  • Helps determine earthquake risk

Earth Science Chapters 5 and 6

using friction
Using Friction
  • Friction
    • The force that opposes the motion of one surface as it moves across another
  • Low friction means stress doesn’t build up, so big earthquakes are unlikely
  • Moderate friction produces occasional small earthquakes
  • High friction causes stress to build up and can cause bigger earthquakes

Earth Science Chapters 5 and 6

predicting earthquakes
Predicting earthquakes
  • Not very accurate yet
  • Better at finding the probability of a strong earthquake occurring
    • But not when it will occur

Earth Science Chapters 5 and 6

discuss3
Discuss
  • A seismograph records a strong earthquake and a weak earthquake. How would the seismograms for the two earthquakes compare?
  • What four instruments are used to monitor faults?

Earth Science Chapters 5 and 6