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Engineering Geology

Engineering Geology. S.Subramanian. STUDY OF INTERIOR OF EARTH. TERMINOLOGIES. SEISMOLOGY: branch of geophysics that deals with the study of seismic waves generated during earthquake. Three types of waves: P-waves, S-waves and L-waves .

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Engineering Geology

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  1. Engineering Geology S.Subramanian

  2. STUDY OF INTERIOR OF EARTH

  3. TERMINOLOGIES • SEISMOLOGY: branch of geophysics that deals with the study of seismic waves generated during earthquake. • Three types of waves: P-waves, S-waves and L-waves. • The P and S waves travel through the body of the earth and hence distinguished as body waves. • The L-waves are confined mostly to near the surface of earth and hence they are called surface waves.

  4. Mohorovicic discontinuity: marks the lower limit of crust P and S waves undergo a sharp increase in their velocities. This layer demarcates the boundary between crust and mantle.

  5. Mantle - Core discontinuity: At a depth 2900 Km, there is another major discontinuity where P waves suffer a decrease in velocities, while, S waves are stopped from travelling further. This discontinuity demarcates the boundary between the mantle and the core.

  6. THE CRUST • It is the uppermost layer of the earth. • The mohorovicic discontinuity marks the lower boundary of the crust. • It is divided into three layers namely, A layer, B layer and C layer

  7. THE MANTLE • It is the second layer of the earth and extends upto 2900 km. • The mantle is the thick layer of hot, solid rock between the Earth's crust and the molten iron core. • It has been subdivided into and upper and lower mantle • Upper mantle • Lithosphere- this is the weak spot in the upper mantle that allows for intrusion and the shifting of plate • Lower mantle • The lower mantle extends from 670 to 2900km. The asthenosphere lies below the lithosphere and represent rock close to its melting point.

  8. THE CORE • It is the inner most layer of the Earth. • The core boundary begins at depth of 2900km from the surface and extends to the center of the earth of 6371 km. • The outer core comprises the region from a depth of 2900km to 4580km below the earth surface and behaves more like a liquid. Inner Core: • The inner core has a thickness of around 1790km and is believed to be a solid metallic body. • The chemical composition of the inner core is chiefly of iron and nickel.

  9. PLATE TECTONICS THEORY

  10. CONTRACTION HYPOTHESIS • The Earth was a ball of molten material at some initial stage of evolution. • The outer portion cooled completely to form Crust. • The inner part remained molten and continued to lose heat and shrank in volume. • The outer core had to fit on a reduced inner surface • Development of compressive forces in the outer crust throwing the crust into block of mountains

  11. CONVECTION CURRENT HYPOTHESIS • Convection currents supposed to exist in plastic type of mantle below the crust. • These currents acquire circulating paths within the mantle. • These circulating currents exert dragging and compressive effects on the crust above.

  12. DRIFT HYPOTHESIS • The outer crust of Earth was a single unit called Pangea. • Pangea was broken by process of rifting. • Great friction developed because of different densities and the frontal edges were thrown into blocks.

  13. PLATE TECTONICS • Earth crust is composed of several rigid but thin plates which are 100 to 150 Km thick and carry both continental and oceanic crust with them. • They are in continuous motion with each other in the plastic part of mantle. • There are seven major crustal plates.

  14. PLATE BOUNDARIES • Depending on the relative motions of adjacent plates, the plate boundaries are classified into two groups. • Divergent boundaries: These are boundaries at which plates move away from each other. • In this process of plate separation, the magma rises up from the mantle and fills the gap created.

  15. Convergent boundaries: • These are boundaries at which plates move towards from each other. • When they collide, one plate moves under the other plate, raising its materials to form a mountain.

  16. PLATE MARGINS • When two plates with continents at leading edge converge, a collision takes place. As a result the crust thickens to form great mountain ranges like Himalayas. They unite to form a single large plate. • Where a continental crust converges with the oceanic crust, the less dense continental mass remains floating while the more dense oceanic crust sinks into the mantle. • Where two oceanic plates converge, one of them is subducted. The magma produced due to melting of the dipping plate, rises to the surface to form volcanoes.

  17. EARTHQUAKES

  18. TERMINOLOGIES • Focus: The place or point of origin of earthquake below the surface of Earth is called focus. • Epicenter: The point or place on the surface vertically above the focus of a particular earthquake is called epicenter.

  19. CLASSIFICATION OF EARTHQUAKES • Earthquakes are classified on a number of bases like depth of focus, the cause of origin, the intensity and magnitude. • DEPTH OF FOCUS • Shallow Earthquake: Depth of focus lies within 60Km below the surface. • Intermediate Earthquake: Depth of focus lies between 60Km to 300Km below the surface. • Deep seated Earthquake: Depth of focus lies between 300Km to 700Km below the surface.

  20. CAUSE OF ORIGIN Tectonic earthquake: These are caused due to faulting of blocks of the crust of Earth along rupture planes. Non tectonic earthquakes: These owe their origin to causes distinctly from faulting such as volcanic eruptions, atomic explosions etc. BASED ON MAGNITUDE

  21. EFFECTS OF EARTHQUAKE • Primary Effects: These include all such effects that are directly related to the cause of origin of earthquakes. These produce many important changes in geologic structures. • Secondary Effects: All those effects which are related to passage of seismic waves and associated shaking motion of ground during earthquake are grouped as secondary effects. Many landslides are triggered and buildings are damaged severely.

  22. VOLCANOES

  23. terminologies • Naturally occurring fissures, conduits or vents through which hot material comes out regularly are termed as Volcanoes. • Liquid Matter: The bulk of the material erupted from the volcanoes are hot, viscous and mobile liquid called LAVA. It is simply the magma that has reached the surface of Earth. • Gases: These generally reach the surface first during volcanic eruptions. The most dominant gas erupted is steam. CO2, N2, CO, SO2 are also found in volcanic eruptions.

  24. Solid Matter: The solid material or pyroclasts thrown out by volcanoes are generally derived from the country rock hosting the volcano. Pyroclastsconsist of fragments of different sizes named differently. The biggest fragments are named volcanic blocks. The finest, dust like materials, are called volcanic dust. When the volcanic dust consolidates it is called volcanic tuff. Solidified clots of lava are thrown out from volcanoes, called volcanic bombs.

  25. TYPES OF ERUPTION • There are three main types of volcanic eruptions namely, central eruption, fissure eruption and fumaroles. • Volcanic Cone: It may be defined as a conical hill of solid volcanic ejecta built around the point of eruption. • Volcanic Craters: These are defined as the openings of volcanoes at the surface. • Calderas: These may also be broadly defined as very large sized craters that have collapsed with the passage of time.

  26. The Central eruptions are classified into four types depending on the nature of eruption. In a Hawaiian eruption, fluid basaltic lava is thrown into the air in jets from a vent. Such an eruption takes place without making much noise. Strombolian Eruption is characterized by a constant and mild eruption of thick type lava which comes out in the form of a viscous paste, often clots, through small sized craters

  27. In VolcanianEruption such an eruption, firstly a lot of pressure is built up below the blocked mouth of the volcano, then suddenly the obstructions are removed and thick black clouds with pyroclastic materials and lava pour out the volcano. Thunderstorms are known to accompany these eruptions. PeleanEruption is the most destructive and at the same time rare type of volcanic eruption. During that explosion, the lava is believed to have travelled downslope with a speed of 150 Km/hr. Lava is in highly fluid condition during this type of eruptions.

  28. FISSURE ERUPTION In these types of eruptions neither cone nor craters are formed. Tremendous volumes of lava simply flow out from fissure and cracks. This continuous flow of lava spreads across the country side in form of sheets burying everything. FUMAROLES These are cracks, fissures in the crust of earth through which only hot gases come out regularly. When there is no lava flow and only gases come out, then the opening is called fumaroles.

  29. VOLCANIC LANDFORMS • Volcanic mountains are huge volcanic cones of varied type of volcanic ejecta, pyroclastic and lava materials. In some cases the cones are made up of fragmentary materials. When basaltic lave is poured out, the mountains have a gentle slope. • Volcanic Plateaus and Plains may be defined as extensive sheet of cooled lava flowing of great thickness. It is the thickness from repeated flows that separates the volcanic plateaus from volcanic plains. • Volcanic Necks are also volcanic products and consist of pipe like masses of lava and frequently cooled materials from the former conduits.

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