lecture02 interior of earth.pptx................

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1. Interior of Earth Crust

2. Interior of earth ? Evidence of interior of earth ? Chemical composition of earth ? At the end of the lecture?

3. Interior of Earth Crust

4. The atmosphere is divided into five layers. It is thickest near the surface and thins out with height until it eventually merges with space. 1) The troposphere is the first layer above the surface and contains half of the Earth's atmosphere. Weather occurs in this layer. 2) Many jet aircrafts fly in the stratosphere because it is very stable. Also, the ozone layer absorbs harmful rays from the Sun. 3) Meteors or rock fragments burn up in the mesosphere . 4) The thermosphere is a layer with auroras. It is also where the space shuttle orbits. 5) The atmosphere merges into space in the extremely thin exosphere . This is the upper limit of our atmosphere.

5. Mass 1.7 % of earths mass Depth from surface :5150-6370 km (1220km) Suspended in molten outer core Inner core

6. Mass 30.8% of earths mass Depth 2890-5150 km (2260km) Molten material Less dense Earth magnetic field Not pure iron ,some other light elements Outer core

7. Mass 3% of earth mass Depth 2700km-2890 km (200-300km) 4 % of mantle –crust mass Part of mantle sink through it but floating on outer core due to its low density as compared to outer core D layer

8. 49.2% mass of total earths mass Depth 650-2890km 72.9% mantle –earth mass Lower mantle

9. Mass 7.5% of earth mass Depth 400-650 km 11.1 % of mantle –crust mass Fertile layer : production of basaltic magma Conversion into dense material Transition region

10. 10.3 % of earth mass Depth 10-400km 15% of mantle –crust mass Asthenosphere Upper mantle

11. .099% of earth mass 0-10 km depth 0.147% of mantle –crust mass Oceanic crust

12. 0.374% of earth mass Depth 0-50km 0.544 % of mantle-crust mass Continental crust

13. Drilling up to 15 KM Direct reach is impossible ? Indirect and accurate evidences for interior. Evidence for earths interior

14. Density Magnetic field Volcano Seismic waves Evidence for earths interior

15. Earth density = 5.5 gram per cubic centimeter Density of crust( continental ) = 2.7 gram per cubic centimeter Density of crust (oceanic part) = 3 gram per cubic centimeter It mean inner rocks are more dense . Density

16. The discovery of the liquid outer core allowed another hypothesis: the geodynamics. Iron, whether liquid or solid, is a conductor of electricity. Electric currents would therefore flow in molten iron. Moving a flowing electric current generates a magnetic field at a right angle to the electric current direction (basic physics of electromagnetism). The molten outer core convicts as a means of releasing heat. This convective motion would displace the flowing electric currents thereby generating magnetic fields. The magnetic field is oriented around the axis of rotation of the Earth because the effects of the Earth's rotation on the moving fluid. Magnetic field

17. A volcano is a rupture on the crust of a planetary mass object, such as the Earth, which allows hot lava ,volcanic ash, and gases to escape from a magma chamber below the surface . Volcano

18. Igneous rocks that have cooled from magma contain lumps of rock of different composition from the magma itself. These lumps are termed xenoliths, which means ‘foreign piece of rock’. The xenoliths are formed when magma rising from deep levels rips off pieces of the rock which it passes through (the country rock) and carries these pieces along with it. Some xenoliths come from deeper levels within the crust, others come from the uppermost mantle, down to depths of about 200 km. The mantle xenoliths show us that the uppermost mantle is made of a rock called peridotite . Xenoliths

19. Oceanic crust is normally destroyed less than 200 Myr (million years) after formation by subduction . An ophiolite is the technical term for a piece of ancient oceanic crust that escaped destruction and was instead shifted onto a continental plate by natural tectonic forces.. Ophiolites

20. Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth. The energy released is in the form of waves by an earthquake Seismic waves

21. There are two types of seismic wave, namely, 1) Body waves 2) Surface waves TYPES OF SEISMIC WAVES

22. There are two types of body waves P-Waves (Primary waves) S-Waves (Secondary waves) Body Waves

23. P waves are longitudinal or compressional waves, which means that the ground is alternately compressed and dilated in the direction of propagation. These waves generally travel slightly less than twice as fast as S waves and can travel through any type of material. In air, these pressure waves take the form of sound waves, hence they travel at the speed of sound. Typical speeds are 330 m/s in air, 1450 m/s in water and about 5000 m/s in granite. P waves are sometimes called "primary waves", These are not as destructive as the S waves and surface waves that follow them. This is the fastest kind of seismic wave. P-Waves

24. Compressional Wave (P-Wave) Deformation propagates. Particle motion consists of alternating compression and dilation. Particle motion is parallel to the direction of propagation (longitudinal). Material returns to its original shape after wave passes.

25. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air. These waves travel at ~6 km/s near the surface to ~10.4 km/s near the Earth’s core about 2900km below the surface. As the waves enter the core, the velocity drops to ~6 km/s increasing to ~11 km/s near the center. Sometimes animals can hear the P waves of an earthquake. Usually we only feel the bump and rattle of these waves. P-Waves

26. where K is the modulus of incompressibility , μ is the modulus of rigidity and ρ the density of the material through which the wave is propagating. Of these density shows the least variation so the velocity is mostly controlled by K and μ . Speed of P-Waves

27. S waves are transverse or shear waves, which means that the ground is displaced perpendicularly to the direction of propagation. S waves can travel only through solids, as fluids (liquids and gases) do not support shear stresses. Their speed is about 60% of that of P waves in a given material. S waves are sometimes called "secondary waves", and are several times larger in amplitude than P waves. S-Waves

28. Shear Wave (S-Wave) Deformation propagates. Particle motion consists of alternating transverse motion. Particle motion is perpendicular to the direction of propagation (transverse).

29. Its name, S for secondary, comes from the fact that it is the second direct arrival on an earthquake seismogram , after the compressional primary wave or P-wave S-Waves

30. These waves travel from ~3.4 km/s near the surface to ~7.2 km/s near the boundary of the liquid core (Gutenberg discontinuity). These waves travel at a slower rate but with greater amplitude . S-Waves

31. There are two major types of Surface waves as follows; Rayleigh waves Love waves Surface Wave

32. Rayleigh waves , also called ground roll, are surface waves that travel as ripples similar to those on the surface of water. The existence of these waves was predicted by John William Strutt , Lord Rayleigh , in 1885 . They are slower than body waves, and supposedly can readily be seen during an earthquake in an open space like a parking lot where the cars move up and down with the waves. A Rayleigh wave rolls along the ground just like a wave rolls across a lake or an ocean. Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Rayleigh Waves

33. Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves. Since Rayleigh waves are surface waves, the strength, or amplitude , of the waves decreases exponentially with the depth of the earthquake. Rayleigh Waves

34. Rayleigh Wave (R-Wave) Deformation propagates. Particle motion consists of elliptical motions (generally retrograde elliptical) in the vertical plane and parallel to the direction of propagation. Amplitude decreases with depth. Material returns to its original shape after wave passes.

35. Love waves are surface waves that cause horizontal shearing of the ground. They are named after A.E.H. Love , a British mathematician who created a mathematical model of the waves in 1911 . They usually travel slightly faster than Rayleigh waves. It's the fastest surface wave and moves the ground from side-to- side. Love Waves

36. Love Wave (L-Wave) Deformation propagates. Particle motion consists of alternating transverse motions. Particle motion is horizontal and perpendicular to the direction of propagation (transverse). To aid in seeing that the particle motion is purely horizontal, focus on the Y axis (red line) as the wave propagates through it. Amplitude decreases with depth. Material returns to its original shape after wave passes.

37. Seismic waves travel more quickly through denser materials and therefore generally travel more quickly with depth. Hot areas slow down seismic waves. Seismic waves move more slowly through a liquid than a solid. Partially molten areas may slow down the P waves and attenuate or weaken S waves.

38. Low Velocity Zone Seismic velocities tend to gradually increase with depth in the mantle due to the increasing pressure, and therefore density, with depth. However, seismic waves recorded at distances corresponding to depths of around 100 km to 250 km arrive later than expected indicating a zone of low seismic wave velocity. Furthermore, while both the P and S waves travel more slowly, the S waves are attenuated or weakened. This is interpreted to be a zone that is partially molten, probably one percent or less (i.e., greater than 99 percent solid).  Alternatively, it may simply represent a zone where the mantle is very close to its melting point for that depth and pressure that it is very "soft."  Then this represents a zone of weakness in the upper mantle. This zone is called the "weak sphere."  

39. Gutenberg Seismic Discontinuity / Core-Mantle Boundary (shadow zone 103 to 143) Seismic waves recorded at increasing distances from an earthquake indicate that seismic velocities gradually increase with depth in the mantle .However, at arc distances of between about 103° and 143° no P waves are recorded. Furthermore, no S waves are record beyond about 103°. Gutenberg (1914) explained this as the result of a molten core beginning at a depth of around 2900 km. Shear waves could not penetrate this molten layer and P waves would be severely slowed and refracted (bent).

40. Core  is made of iron with minor amounts of nickel, and lies at the center of the earth Mantle  is made of iron-magnesium silicates and surrounds the core. The mantle makes up the bulk of the earth. Crust  occurs as two distinct types, oceanic crust and continental crust. Both types of crust are lighter (less dense) and contain more silica than the mantle. Oceanic crust  is the crust that underlies most of the areas we call "oceans" it is thinner, is more dense, and contains less silica and aluminum and more magnesium and iron than continental crust. The lack of silica makes it darker than continental crust.   Because  continental crust  is thicker and made of less dense material than the oceanic crust, it "floats" higher on the earth. Chemical composition