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Transcript
Tectonics Earthquakes Earthquakes are vibrations caused by earth movements at plate boundaries and at major fault lines (cracks in the earth’s surface). They can occur at all 3 major plate boundaries but the most severe earthquakes are normally found at conservative and convergent plate boundaries. conservative convergent Tectonics How do they happen? Tectonics How do they happen? Tectonics What causes this to happen? • It occurs because there is a fracture (break) or sudden movement in the Earth’s crust. • This usually happens because the plates that make up the Earth’s crust are moving. THE EARTH’S CRUST The focus is the place where the fracture or break actually happens inside the crust. An earthquake is the shaking of the ground due to a sudden release of energy. Tectonics How do they happen? THE EARTH’S CRUST The further the waves travel the more energy they lose and the less damage they are likely to do. The epicentre is the place on the surface, directly above the focus, where the earthquake waves are first felt. Earthquake waves spread out from the focus, like ripples on a pond. The focus. Tectonics How do they happen? Tectonics How do they happen? Tectonics How do we measure them? Tectonics How do we measure them? The Richter Scale This measures the magnitude of a tremor (how powerful it is) using an instrument called a seismograph. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. Although the Richter Scale has no upper limit, the largest earthquake ever recorded was in 1960 in Chile. It measured 9.5 on the Richter Scale. It is a logarithmic scale which means that a size ‘6’ on the Richter Scale is 10 times larger than a size ‘5’ and 100 times larger than a size ‘4’. The Mercalli Scale The Mercalli scale measures how much damage is caused by the earthquake based on observations. It is measured on a scale between 1 and 12. Tectonics Putting it into context… Tectonics Putting it into context… Tectonics Putting it into context…