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Chapter Eleven - Geophysical Properties of Planet Earth.

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Presentation on theme: "Chapter Eleven - Geophysical Properties of Planet Earth."— Presentation transcript:

1 Chapter Eleven - Geophysical Properties of Planet Earth


3 Exploring the Interior of the Earth Geophysics- the study of the foundational properties of the Earth’s interior. Geophysicists- identify thickness, density, composition, structure and physical state of the layers of the Earth’s interior Knowledge of Earth’s interior comes mainly from seismological station that records seismic body waves.  Analysis of waves arrival time recorded by seismographs  Seismic tomography- using same principles similar to CAT Scans to generate 3-D images of the Earth’s interior P-wave travels through solid and liquid while S-wave travels only through solids Refraction and reflection occur at contacts between different layers

4 Earth’s Interior Inaccessibility of Earth’s Interior Deepest hole drilled ~ 13 km General observations about Wave Propagation: – P waves compress mail material through which they travel; Medium returns to original volume; Travel through sold (Elastic) faster than Liquid or Gas (inelastic) – S waves travel as shear waves; admitted by elasticity of solids; omitted by inelasticity of liquid or gas; seismic wave velocity increases with depth

5 Earth’s Layers Earth is divided into continental and oceanic crust between different composition thickness & structure Seismic discontinuity- MOHO- boundary between crust and mantle Transitional zone within the mantle (slowing) Crust- silica rich igneous/metamorphic rocks- continental km ( mi) ~2.7-3g/cm 3 ; oceanic- density 3.0 3 Mantle- upper 3.3 g/cm 3 up to 400 km and more. Lower P velocity at boundary between mantle and core km ( mi) Asthenosphere-region ( km ( mi)) where P & S slow down Seismic discontinuity- mantle core

6 Earth’s layers-contd. Crust composed of Silicate-rich igneous rocks Sampled directly by drilling Studied extensively by seismic analysis P-waves: ~6 km/s in continental crust; ~ 7 km/s in oceanic crust Continental Crust: Thickness varies between km; P-wave velocity varies between 6-7 km/s; density: g cm -3 Oceanic Crust: Studied by Deep-Sea Drilling; seismic analysis; 200-m deposit marine sed; 2-km layer of pillow sediment;6-km layer of Gabbro; aver. Den. ~ 3 g cm -3 ;

7 Earth’s layers-contd. Crust-Mantle Boundary: Moho discontinuity Mantle: Density varies – g cm -3 ; composed of elastic/plastic solids; Changes in P- & S-wave velocities reveal mantle layers; P- wave velocity from Moho to Asthenosphere: km/s; P-wave velocity in Asthenosphere: < 8 km/s; Asthenosphere is partially molten because of unique temperature and pressure combination Transition Zone: Below Asthenosphere; At 400- km, Mg olivine compresses to form spinel; At 700-km, spinel and other minerals change to metallic oxides

8 Ultramafic mantle minerals collapsing

9 Earth’s Mantle-Core Boundary

10 Earth’s layers-contd. Lower Mantle: 700-2,900 km deep; P-wave velocity from Asthenosphere to base of mantle: km/s; composed of dense Mg silicates and oxides Mantle-Core Boundary: P-wave velocity slows from 13.6 to 8.1 km/s; S-waves cease; Outer core: Liquid Iron-Nickel mix, density g cm -3 CORE: 1/6 TH Earth’s volume, 1/3 RD Of the Earth’s Mass; Pressure >3 Million atmosph.; Temp.~4,700ºC; Composition: IRON-NICKEL, Consistent with Seismic data, meteorite data, and mathematical model

11 Velocity Change between layers

12 Three major components of the Earth

13 Seismic Wave

14 The low-velocity zone

15 Shadow Zones Shadow zones-  segments of the earth opposite an Earthquake’s focus where no direct S & P waves can be received S-Shadow zone-  produced because shearing S-wave cannot travel through liquid, hence S-Shadow zone occurs P-Shadow zones-  are produced as P-waves are refracted when they enter a zone of lower rigidity  both zones help to confirm that earth’s outer core is liquid

16 Shear Waves – Shadow zone

17 Shear Waves – contd.

18 P-Waves Globe

19 P-waves Cut-away

20 The Behavior of P- and S-waves

21 Solid Inner Core

22 Gravity Force of attraction that an object (A) exerts on another object (B), i.e. Force of gravity is proportional to mass of A x mass of B distance 2 Gravimeter- measures variation in Earth’s gravity.  Gravity depends on the altitude of the land, latitude, and distance from the Earth’s center of gravity. Gravity anomalies-  difference between actual gravimetric measurement to the expected theoretical values- positive attraction will be lower than expected and negative attraction higher than expected

23 Gravitation attraction of the earth

24 Gravitation-contd. Isostacy- equilibrium between lithospheric segments and the asthenosphere beneath them Magnetism- force associated with moving charged particles that enables certain substances to attract or repel similar materials- magnetic reversal, paleomagnetism

25 Negative Gravity anomaly

26 Positive Gravity anomaly

27 Positive gravity anomaly over ore deposit

28 Principle of isostacy - icebergs

29 Principle of isostacy - mountains

30 Isostatic adjustments

31 Magnetic field of a bar magnet

32 Prevailing Magnetic Field

33 Electrically conductive field

34 Magnetic field polarity within magnetite

35 Terrestrial record of magnetic reversal

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