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Chapter 10 Objectives 1. Discuss the elastic rebound theory. 2. Explain why earthquakes generally occur at plate boun

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Chapter 10 Objectives 1. Discuss the elastic rebound theory. 2. Explain why earthquakes generally occur at plate boundaries. 3. Compare the 3 types of seismic waves. 4. Discuss the method scientists use to pinpoint an Earthquake (EQ).

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Presentation Transcript
slide1
Chapter 10 Objectives

1. Discuss the elastic rebound theory.

2. Explain why earthquakes generally occur at plate boundaries.

3. Compare the 3 types of seismic waves.

4. Discuss the method scientists use to pinpoint an Earthquake (EQ).

5. Discuss the method most commonly used to measure the magnitude of EQs.

earthquakes plate tectonics
Earthquakes & Plate Tectonics
  • Earthquakes (EQs):vibrations of the Earth’s crust
    • Occur when rocks under stress suddenly shift
slide3
Elastic Rebound Theory: the theory geologists use to explain many EQs
    • Rocks on each side of fault are moving
    • If fault is locked, stress increases
    • At certain point rocks fracture & rebound
slide6
Aftershocks: series of smaller tremors.
    • Caused by released energy (seismic waves)
      • Increases stress in other rocks along the fault
slide7
Focus depths vary
    • Shallow focus - w/in 70 km of surface
      • Tend to cause the most damage
slide8
Focus depths vary
    • Intermediate focus - 70 to 300 km
slide9
Focus depths vary
    • Deep focus (occur in subduction zone)
      • 300 to 650 km
slide10
Focus depths vary
    • About 90% of Continental EQs are shallow focus
3 major eq zones
3 Major EQ Zones
  • Links btwn EQs & Plate Tectonics
    • Plate movements = stress buildup
slide14
3. Eurasian-Melanesian mountain belt: Eurasian plate colliding w/African & Indian plates = stress
slide15
Fault Zones: are groups of interconnected faults.
    • Form at plate boundaries b/c of intense stress
      • e.g. San Andreas fault
slide16
Not all EQs occur at plate boundaries!
    • e.g. New Madrid, Missouri, 1812
      • Ancient fault? (600 million yrs ago)
3 major types of seismic waves
3 major Types of Seismic Waves
  • P waves:primary wave.
    • Move fastest
    • 1st to be recorded
    • Travels through solids & liquids
      • More rigid matl. = faster
3 major types of seismic waves1
3 major Types of Seismic Waves
  • S waves:secondary waves.
    • 2nd waves to be recorded
    • Only travel through solids
3 major types of seismic waves2
3 major Types of Seismic Waves
  • L waves:surface waves, also called long waves.
    • Converted from P & S waves when they reach the surface
    • Slowest-moving waves
      • Last to be recorded
    • Cause surface to rise & fall
recording eqs
Recording EQs
  • Seismograph: instrument used to detect and record seismic waves.
    • 3 separate devices
      • 1 records vert. motion
      • 2 record horz. motion
        • One N to S
        • One E to W
locating an eq
Locating an EQ
  • Scientists compare time diff. btwn P & S waves.
    • Plot on graph to get distance to epicenter
locating an eq1
Locating an EQ
  • Need 3 plots to locate epicenter
    • Point where all 3 circles meet is location of epicenter
slide28

Blue primary waves followed by red secondary waves move outward in concentric circles from the epicenter of an earthquake off British Columbia and Washington State.

eq measurement
EQ Measurement
  • Richter Scale: used to express magnitude of an EQ.
    • Measure of energy released
eq measurement1
EQ Measurement
  • Richter Scale: used to express magnitude of an EQ.
    • Measure of energy released
    • Major EQ = 7 or above
      • Causes widespread damage
eq measurement2
EQ Measurement
  • Richter Scale: used to express magnitude of an EQ.
    • Measure of energy released
    • Moderate EQ = 6 to 7
eq measurement3
EQ Measurement
  • Richter Scale: used to express magnitude of an EQ.
    • Measure of energy released
    • Minor EQ = 2.5 to 6
eq measurement4
EQ Measurement
  • Richter Scale: used to express magnitude of an EQ.
    • Measure of energy released
    • Microquakes = < 2.5
      • Not felt by people
eq measurement5
EQ Measurement
  • Mercalli Scale: expresses the intensity of an EQ.
  • Intensity: the amount of damage the EQ causes.
    • Roman numerals from I to XII

Seismic Monitor

earthquake damage
EARTHQUAKE DAMAGE
  • Movement of the ground itself seldom causes many deaths or injuries.
  • Most injuries result from the collapse of the buildings, flying glass and falling objects.
earthquake damage1
EARTHQUAKE DAMAGE

EQs and under water landslides can cause huge ocean waves called tsunamis. Tsunamis can cause massive death and damages.