Interior of the earth

EARTH INTERNAL STRUCTURE

1. INTERNAL STRUCTURE OF THE EARTH AND SEISMIC WAVES Department of Geology Guided by Presented by Prof. L alsingh Solanki Vishal Choudhary Class – M.Sc. (1 st sem . ) Govt. Holkar Science College Indore (M.P.)

2. CONTENT Introduction Compositional elements of the earth Interior of the earth Chemical composition and layering system of the earth seismic waves seismic wave propagation Significance of seismic waves Comparison of earth internal structure with the moon References

3. INTRODUCTION Three centuries ago, the English scientist Isaac Newton calculated, from his studies of planets and the force of gravity, that the average density of the Earth is twice that of surface rocks and therefore that the Earth's interior must be composed of much denser material . Our current information comes from studies of the paths and characteristics of earthquake waves travelling through the Earth, as well as from laboratory experiments on surface minerals and rocks at high pressure and temperature.

4. Other important data on the Earth's interior come from geological observation of surface rocks and studies of the Earth's motions in the Solar System, its gravity and magnetic field, and the flow of heat from inside the Earth. Earth is made up of three main shells: the very thin, brittle crust, the mantle, and the core; the mantle and core are each divided into two parts . Although the core and mantle are about equal in thickness, the core actually forms only 15 percent of the Earth's volume, whereas the mantle occupies 84 percent.

5. COMPOSITIONAL ELEMENTS OF THE EARTH Carbon-containing compounds that either occur in living organisms, or have characteristics that resemble those of molecules in living organisms, are called organic chemicals. Examples include oil, protein, plastic, fat, and rubber. ORGANIC CHEMICALS

6. MINERAL : A solid substance in which atoms are arranged in an orderly pattern is called a mineral. . CRYSTAL: A single coherent sample of a mineral that grew to its present shape and has smooth, flat faces is a crystal. GRAIN : An irregularly shaped sample, or a fragment derived from a once-larger crystal or group of crystals, is a grain. GLASSES : A solid in which atoms are not arranged in an orderly pattern is called glass. Glass forms when a liquid freezes so fast that atoms do not have time to organize into an orderly pattern.

7. ROCKS : Aggregates of mineral crystals or grains, and masses of natural glass, are called rocks. Geologists recognize three main groups of rocks. (1) Igneous rocks (2) Sedimentary rocks (3) Metamorphic rocks . METALS : Metals are opaque, lustrous elements that are good conductors of heat and electricity. ALLOY : An alloy is a mixture containing more than one type of metal atom (e.g., bronze is a mixture of copper and tin). MELTS: Melts form when solid materials become hot and transform into liquid. Molten rock is a type of melt . VOLATILES : Materials that easily transform into gas at the relatively low temperatures found at the Earth’s surface are called volatiles.

8. INTERIOR OF THE EARTH THE CRUST THE MANTLE THE CORE

9. THE CRUST Crust is the outer thin layer of rock which forms a thin skin on the earth surface , with a total thickness normally between  30-50 km . Crust is thinner beneath the oceans than beneath the continent. Oceanic crust is  thinner (5-30 km thick)  as compared to the continental crust  (50-70 km thick). The continental crust is thicker in the areas of major mountain systems. -100 km thick in the Himalayan region.

10. Mohorovicic ( Moho ) discontinuity  forms the boundary  between crust and asthenosphere  [ asthenosphere is a part of mantle ]. The outer covering of the crust is of  sedimentary material (granitic rocks)  and below that lie crystalline, igneous and metamorphic rocks which are  acidic  in nature. The lower layer of the crust consists of  basaltic and ultra-basic rocks. The continents are composed of lighter silicates—silica + aluminium (also called  ‘ sial ’ ) while the oceans have the heavier silicates—silica + magnesium (also called ‘ sima ’ ).

11. CHARACTERSTICS OF OCEANIC AND CONTINENTAL CRUST CHARACTERSTICS OCEANIC CRUST CONTINENTAL CRUST AVERAGE THICKNESS 7 Km 20 to 70 Km (thickest under mountain) seismic P- WAVES 7Km/Second 6 Km/Second (higher in lower crust) DENSITY 3.0 gm/(cm)3 2.7 gm/(cm)3 PROBABLE COMPOSITION Basalt underlain by gabbro Graite,other plutonic rocks ,schist ,gneiss (with sedimentary rock cover)

12. CONTINENTAL AND OCEANIC CRUST

13. THE MANTLE The Mantle extends from  Moho’s discontinuity  (35 km) to a depth of  2,900 km ( Moho -Discontinuity to the  outer core). The crust and the uppermost part of the mantle are called  lithosphere. Its thickness ranges from  10-200 km. The lower mantle extends beyond the asthenosphere.It is in  solid state. The density of mantle varies between 2.9 and 3.3 .

14. The density ranges from 3.3 to 5.7 in the lower part. It is composed of solid rock and magma. It forms  83 per cent  of the earth’s volume. The outer layer of the mantle is partly  simatic  while the inner layer is composed of wholly  simatic ultra-basic rocks . Earth's mantle plays an important role in the Evolution of the crust and provides the thermal and mechanical driving forces for plate tectonics.

15. ASTHENOSPHERE The  upper portion of the mantle  is called A sthenosphere . The word astheno means weak. It is considered to be extending up to 400 km. It is the  main source of magma  that finds its way to the surface during volcanic eruptions. It has a density higher than the crust’s.

16. THE CORE Lies between  2900 km and 6371 km  below the earth’s surface. Accounts for  16 per cent  of the earth’s volume. Core has the heaviest mineral materials of highest density. It is composed of  nickel and iron [nife]. The  outer core is liquid  while the  inner core is solid. A zone of mixed heavy metals + silicates separates the core from outer layers.

17. The core is the densest layer of the earth with its density ranges between 9.5-14.5g/cm3. The Core consists of two sub-layers: the inner core and the outer core. The inner core is in solid state and the outer core is in the liquid state (or semi-liquid). The discontinuity between the upper core and the lower core is called as  Lehmann Discontinuity. Barysphere   is sometimes used to refer the core of the earth or sometimes the whole interior.

18. FIG - INTERIOR OF THE EARTH

19. CHEMICAL COMPOSITION AND LAYERING SYSTEM OF THE EARTH The crust is covered by a thin layer of sedimentary rocks of very low density. This layer is composed of crystalline rocks , mostly silicate matter . The upper part of this layer is composed of light silicate matter while heavy silicate matter dominated in the lower part. According to Suess

20. SIAL Located just below the outer sedimentary cover is composed of granites. Dominated by silica and aluminium , acid materials and silicate of K ,Na and Al(SIAL=SI+AL). The average density is 2.9 ,thickness ranges between 50-300km. Continents have been formed by sialic layer.

21. SIMA Composed of basalt and the sources of magma and lava during volcano eruption. Dominated by silica and magnesium . Average density ranges between 2.9 to 4.7 and thickness from 1,000 Km to 2,000 Km . There is abundance of basic matter . The silicate of Mg, Ca and Fe are most abundantly found.

22. NIFE Composed of nickel (Ni) and iron (Fe) . Made up of heavy materials have thus have high density (11). The diameter of this zone is 6880 km. The presence of the iron indicates the magnetic property of the earth interior. This property also indicate the rigidity of the earth.

23. SEISMIC WAVES The different types of tremors and waves generated during the occurrence of an earthquake are called seismic WAVES . The place of the occurrence of an earthquake is called FOCUS and the place which experiences the seismic events first is called EPICENTRE which is located on the earth surface and is always perpendicular to the focus. The deepest focus has been measured at the depth of 700 km from the earth surface .

24. PRIMARY WAVES P-waves are the first waves to arrive on a complete record of ground shaking because they travel the fastest. They typically travel at speeds between ~1 and ~14 km/sec. The slower values corresponds to a P-wave traveling in water, the higher number represents the P-wave speed near the base of Earth's mantle . The velocity of a wave depends on the elastic properties and density of a material . The vibration caused by P waves is a volume change, alternating from compression to expansion in the direction that the wave is traveling. P-waves travel through all types of media - solid, liquid, or gas.

25. FIG - As a P-wave passes the ground is vibrated in the direction that the wave is propagating.

26. SECONDARY WAVES Secondary , or S waves, travel slower than P waves and are also called "shear" waves because they don't change the volume of the material through which they propagate, they shear it. S-waves are transverse waves because they vibrate the ground in a the direction "transverse", or perpendicular, to the direction that the wave is traveling. Typical S-wave propagation speeds are on the order of 1 to 8 km/sec. The lower value corresponds to the wave speed in loose, unconsolidated sediment, the higher value is near the base of Earth's mantle. An important distinguishing characteristic of an S-wave is its inability to propagate through a fluid or a gas because a fluids and gasses cannot transmit a shear stress and S-waves are waves that shear the material.

27. FIG - As a transverse wave passes the ground perpendicular to the direction that the wave is propagating. S-waves are transverse waves.

28. Love waves are transverse waves that vibrate the ground in the horizontal direction perpendicular to the direction that the waves are traveling.  They are formed by the interaction of S waves with Earth's surface and shallow structure and are dispersive waves. The typical range of velocities is between 2 and 6 km/second. The amplitude of ground vibration caused by a Love wave decreases with depth - they're surface waves. Like the velocity the rate of amplitude decrease with depth also depends on the period . LOVE WAVES

29. RALEIGH WAVES Rayleigh waves are the slowest of all the seismic wave types and in some ways the most complicated. Like Love waves they are dispersive so the particular speed at which they travel depends on the wave period and the near-surface geologic structure, and they also decrease in amplitude with depth. Typical speeds for Rayleigh waves are on the order of 1 to 5 km/s.

30. LOVE AND RAYLEIGH WAVE

31. SEISMIC WAVE PROPAGATION Several types of interaction between waves and the subsurface geology (i.e. the rocks) are commonly observable on seismograms. Refraction Reflection Dispersion Diffraction Attenuation

32. FIG - Wave propagation (interior of the earth)

33. SHADOW ZONE A shadow zone is where waves of certain types don’t reach the surface relative to another place on the surface (about 105 degrees from center). The refraction properties at the boundaries between each layer create this “shadow zone,” from which geologists can infer that there is a liquid layer of the core (the outer layer).The Earth has to have a molten, fluid core to explain the lack of S waves in the shadow zone, and the bending of P waves to form their shadow zone.

34. SIGNIFICANCE OF THE seismic WAVES Study the internal structure of the earth. Identifying the oil traps . Identifying the ground water level. Study the E arthquake .

35. COMPARISON OF INTERNAL STRUCTURE OF THE EARTH AND THE MOON All of the terrestrial planets have a three-part layered structure. At the center is a metallic, iron-rich core, part of which may be molten. Above the core is a thick middle layer called the mantle, made of silicate rock (composed mostly of silicon, oxygen, iron, and magnesium), making up most of the bulk of the planet. Above the mantle is a relatively thin crust of less-dense rocky material. The crust has more lighter elements (aluminum, sodium, calcium, sulfur) than the mantle

36. INTERIOR STRUCTURE OF THE EARTH,MOON AND MARS

37. INTERNAL STRUCTURE OF MOON "We applied tried and true methodologies from terrestrial seismology to this legacy data set to present the first-ever direct detection of the moon's core," said Renee Weber, lead researcher and space scientist at NASA's Marshall Space Flight Center in Huntsville, Ala.

38. hthand Apollo 11 astronaut Buzz Aldrin with the seismic experiment. Solar panels have deployed on the left and right and the antenna is pointed at Earth. The laser reflector is beyond the antenna and, in the distance, the TV camera is silhouetted against the black sky. The stereo close-up camera is near the righthand edge of this detail . BY – NASA

39. REFERENCES Diane H.Carlson ; Charles C. Plummer; Lisa Hammersley ; 2010. Physical Geology: Earth Revealed , Ninth Edition; McGraw Hill companies. Stephen Marshal (2008). Earth: Portrait of a Planet Third Edition; W.W Nortan & Company. Singh Savindra (2015) . Physical Geography By Pravalika Publications Allahabad. https://www.nasa.gov/ http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html