GEOL3025, Section 096 Lecture #19 18 October 2007
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Transcript of GEOL3025, Section 096 Lecture #19 18 October 2007
GEOL3025, Section 096Lecture #19
18 October 2007
GEOL3025, Section 096Lecture #19
18 October 2007
Dr. Lysa ChizmadiaDr. Lysa Chizmadia
Measuring Earthquake SizesMeasuring Earthquake Sizes Intensity Scale
Mercalli Intensity Scale Based on destruction of buildings
Magnitude Scales Richter Magnitude (logarithmic) Based on the Amplitude of the largest
seismic wave recorded on seismogram
Intensity Scale Mercalli Intensity Scale Based on destruction of buildings
Magnitude Scales Richter Magnitude (logarithmic) Based on the Amplitude of the largest
seismic wave recorded on seismogram
Mercalli Intensity Scale
Mercalli Intensity Scale
Richter Magnitude Scale
Richter Magnitude Scale
Earthquake DestructionEarthquake Destruction
Seismic Vibrations Tsunami Landslides & Ground Subsidence Fire
Seismic Vibrations Tsunami Landslides & Ground Subsidence Fire
Formation of TsunamisFormation of Tsunamis
Global Distribution of Earthquakes
Global Distribution of Earthquakes
Evidence for Plate TectonicsEvidence for Plate Tectonics
Chapter 12: Earth’s InteriorChapter 12: Earth’s Interior
Propagation of Seismic Waves
Propagation of Seismic Waves Velocity of seismic
waves depends on density (ρ) & elasticity of material
Velocity of waves increases with depth b/c pressure (P) makes rocks more elastic
Refraction of waves occurs when they pass from one material to another
Velocity of seismic waves depends on density (ρ) & elasticity of material
Velocity of waves increases with depth b/c pressure (P) makes rocks more elastic
Refraction of waves occurs when they pass from one material to another
P waves travel through both liquids & solids
S waves travel only through solids
P waves travel faster than S waves in all materials
P waves travel through both liquids & solids
S waves travel only through solids
P waves travel faster than S waves in all materials
P wavesP waves P waves
Compressional First to arrive
(primary) Travel through both
liquids & solids
P waves Compressional First to arrive
(primary) Travel through both
liquids & solids
S wavesS waves S waves
Shear waves Second to arrive Travel through
solids only
S waves Shear waves Second to arrive Travel through
solids only
Propagation of WavesPropagation of Waves Through Uniform
Solid Constant velocity
with depth
Through Uniform Solid
Constant velocity with depth
Through Solid of Increasing P
Increasing velocity with depth
Through Solid of Increasing P
Increasing velocity with depth
Wave Propagation Through Earth
Wave Propagation Through Earth
Because Earth has differentiated, waves travel at different speeds through the different layers
Because Earth has differentiated, waves travel at different speeds through the different layers
Layers Defined by Composition
Layers Defined by Composition
Crust: 3-70 km thick outer skin
Mantle: 70-2900 km solid silicate-rich shell
Core: Fe-rich sphere with 3486 km radius
Crust: 3-70 km thick outer skin
Mantle: 70-2900 km solid silicate-rich shell
Core: Fe-rich sphere with 3486 km radius
Layers Defined by Physical Properties (Seismic Waves)Layers Defined by Physical Properties (Seismic Waves)
Lithosphere: 3-250 km thick crust &
uppermost mantle Cold and rigid
Asthenosphere: 250-660 km lower upper
mantle Warm and soft
Mesosphere: (lower mantle) 660-2900 km lower mantle More rigid than
asthenosphere due to increased P
Lithosphere: 3-250 km thick crust &
uppermost mantle Cold and rigid
Asthenosphere: 250-660 km lower upper
mantle Warm and soft
Mesosphere: (lower mantle) 660-2900 km lower mantle More rigid than
asthenosphere due to increased P
Inner Core: 2270 km thick Liquid b/c s-waves don’t
penetrate Convection produces
Earth’s magnetic field Outer Core:
Fe-Ni metallic sphere with radius of 3486 km
Solid because of increased P
Inner Core: 2270 km thick Liquid b/c s-waves don’t
penetrate Convection produces
Earth’s magnetic field Outer Core:
Fe-Ni metallic sphere with radius of 3486 km
Solid because of increased P
Earth’s LayersEarth’s Layers
Earth’s Major BoundariesEarth’s Major Boundaries The Mohorovičič discontinuity (Moho)
Divides Crust from Mantle Seismic velocities higher in Mantle so deeper
waves arrive earlier Core-Mantle Boundary
P-wave shadow zone 105°-140° Due to high refraction of waves
S-waves do not penetrate at all Inner-Outer Core
P-waves reflected off surface of solid inner Core
P-waves faster in inner Core than in outer Core
The Mohorovičič discontinuity (Moho) Divides Crust from Mantle Seismic velocities higher in Mantle so deeper
waves arrive earlier Core-Mantle Boundary
P-wave shadow zone 105°-140° Due to high refraction of waves
S-waves do not penetrate at all Inner-Outer Core
P-waves reflected off surface of solid inner Core
P-waves faster in inner Core than in outer Core
The MohoThe
Moho
Core-Mantle
Boundary
Core-Mantle
Boundary
Core-Mantle BoundaryCore-Mantle Boundary
Discovery of Inner
Core
Discovery of Inner
Core