Understanding earthquakes

Understanding earthquakes By the end of the end of the lesson you should be able to: Define the terms: earthquake, seismic wave, focus, epicentre, seismometer, magnitude, Richter scale. Explain what causes an earthquake and why everything shakes. Discover what the Richter scale is and how an earthquake’s power can be measured. Give examples of damage caused by earthquakes

What are Earthquakes? Convergent Earthquakes are vibrations caused by earth movements at plate boundaries and at major fault lines (cracks in the earth’s surface). Transform They can occur at all major plate margins but the most severe earthquakes are normally found at Convergent and Transforn boundaries.

Why do earthquakes happen? 1. The two plates at a plate boundary cannot move past each other easily. 2.The two plates lock together. Friction causes pressure to build up. 3. Suddenly the pressure is released and the plates jolt into a new position. 4. This causes seismic waves. The vibrations they cause are called an earthquake.

Anatomy of an Earthquake An Earthquake is the shaking of the ground caused by sudden motions along faults, or fractures in the Earth’s crust. Fault A fracture in the rocks that make up the Earth’s crust. Plates Massive rocks that make up the outer layer of the Earth’s surface and whose movement along faults trigger earthquakes. Epicentre The point at the Earth’s surface directly above the focus. Seismic Waves Waves that transmit the energy released by an earthquake. Focus The point within the Earth where an Earthquake rupture starts.

A Forest Town B Epicentre Focus An earthquake has occurred along this fault line. Match the letter with the correct label.

How are earthquakes measured? 1 2 3 4 6 5 9 8 7 10 The Richter Scale measures the magnitude of a tremor (how powerful it is) using an instrument called a seismometer The Richter Scale is measured on a scale from 1 to 10. It is a logarithmic scale which means that a size ‘6’ on the Richter Scale is 10 times more powerful than a size ’5’ and 100 times more powerful than a size ‘4’. (go up or down by a factor of 10) Richter Scale The largest earthquake ever recorded was in Chile. It measured 9.5 on the Richter Scale.

How many times greater was the Japan earthquake? 1 2 3 4 6 5 9 8 7 10 The earthquake in Italy (August 2016) measured 6.2 on the Richter Scale. The Japan earthquake (March 2011) measured 9.0 on the Richter Scale. Richter Scale How many times greater was the Japan earthquake?

Damage caused by Earthquakes

Show what you have learned Explain what causes an earthquake and why everything shakes. Draw and label a cross section of a Convergent margin showing the following information. The location of the fault line and the two tectonic plates. Where the epicentre and focus of an earthquake are likely to occur. Show the pattern of the seismic waves caused by an earthquake. Define the terms epicentre, focus and seismic waves. Explain what a seismometer is used for and how the magnitude of an earthquake can be measured. Give some examples of damage caused by earthquakes