Chapter 10 Objectives
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Chapter 10 Objectives 1. Discuss the elastic rebound theory. 2. Explain why earthquakes generally occur at plate boundaries. PowerPoint PPT Presentation


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

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Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • 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


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • 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


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • Focus: the area along a fault where slippage 1st occurs.

    • Depths vary


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • Epicenter: the point on the Earth’s surface directly above the focus.


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • Aftershocks: series of smaller tremors.

    • Caused by released energy (seismic waves)

      • Increases stress in other rocks along the fault


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • Focus depths vary

    • Shallow focus - w/in 70 km of surface

      • Tend to cause the most damage


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • Focus depths vary

    • Intermediate focus - 70 to 300 km


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • Focus depths vary

    • Deep focus (occur in subduction zone)

      • 300 to 650 km


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • 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


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • 1. Pacific Ring of Fire: ring of tectonic/volcanic activity surrounding the pacific.


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • 2. Mid-ocean ridges: spreading motion = stress


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • 3. Eurasian-Melanesian mountain belt: Eurasian plate colliding w/African & Indian plates = stress


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • Fault Zones: are groups of interconnected faults.

    • Form at plate boundaries b/c of intense stress

      • e.g. San Andreas fault


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • 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


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

  • Seismogram: seismograph’s record of waves; has wavy lines recorded on paper.


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


Chapter 10 objectives 1 discuss the elastic rebound theory 2 explain why earthquakes generally occur at plate boundaries

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.


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