1 Earthquakes 1 of 44 © Boardworks Ltd 2006

2 Learning objectives What are earthquakes and where do they occur?What causes earthquakes? How are earthquakes measured? What is the difference between the epicentre and the focus? Learning objectives

3 Important Words!!! Epicentre – The point on the Earth’s surface where the earthquake occurred. Focus – The point on the Earth’s crust directly below the epicentre. Seismograph – Measures and records the intensity of an earthquake. Richter Scale – Measures the strength of an earthquake. Primary Effects – The effects of an earthquake that happens immediately and are due to the shaking of the ground. Secondary Effects – The effects of an earthquake that happens afterwards and are a result of the damage done by the initial tremors.

4 What are earthquakes? conservative destructive CollisionEarthquakes 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 four major plate boundaries but the most severe earthquakes are normally found at conservative, destructive and collision plate boundaries. conservative destructive Collision

5 Destructive plate boundaryEarthquake zones

6 Conservative plate boundaryEarthquake zones

7 Collision plate boundaryEarthquake zones

8 Learning objectives What are earthquakes and where do they occur?What causes earthquakes? How are earthquakes measured? What is the difference between the epicentre and the focus? Learning objectives

9 Cause of an Earthquake Rock under stress by plate movementRocks start to deform and fold Eventually the rock breaks and……… …stored energy is released as shockwaves

10 Why do earthquakes happen?

11 Why do earthquakes happen?

12 Why do earthquakes happen?

13 Learning objectives What are earthquakes and where do they occur?What causes earthquakes? What is the difference between the epicentre and the focus? How are earthquakes measured? Learning objectives

14 Epicentre and focus The focus is the point at which the rock moves.Seismic waves start at the focus. The epicentre is directly above the focus on the earth’s surface.

15 Features of an Earthquake

16 Epicentre and focus

17 Epicentre and focus An earthquake has occurred in this area.Which area (the town or the forest) will receive the stronger earthquake? Which area will receive more damage from the earthquake?

18 Epicentre and focus If the epicentre of an earthquake is at ‘A’, which settlement will be damaged the most? Give reasons for your answer.

19 Learning objectives What are earthquakes and where do they occur?What causes earthquakes? What is the difference between the epicentre and the focus? How are earthquakes measured? Learning objectives

20 How can we measure earthquakes?The Richter Scale This measures the magnitude of a tremor (how powerful or strong 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’. Largest earthquakes list - While all care is taken to ensure web links contain useful information, Boardworks does not take responsibility for the content or accuracy of external web sites.

21 How can we measure earthquakes?The Japanese earthquake in Kobe (September 1995) measured 7.2 on the Richter Scale. The Greek earthquake (June 1995) measured 6.2 on the Richter Scale. How many times greater was the Japanese earthquake? The Japanese earthquake was 10 times more powerful than the Greek earthquake.

22 A seismograph

23 Mercalli Scale The Mercalli scale measures how much damage (the effect) is caused by the earthquake based on observations. It is measured on a scale between 1 and 12. Mercalli Scale

24 Task Design your own Mercalli Scale using Microsoft PowerPoint.Gather relevant pictures from the internet. Use the descriptions below as added annotations to your work. For each category below, provide at least 4 pictures and indicate when and where the earthquake took place. I Felt by almost no one. II Felt by very few people. III Tremor noticed by many, but they often do not realise it is an earthquake. IV Felt indoors by many. Feels like a truck has struck the building. V Felt by everyone; many people are awakened. Swaying trees and poles may be observed. VI Felt by all; many people run outdoors. Furniture is moved. VII Everyone runs outdoors. Poorly built structures considerably damaged. Slight damage elsewhere. VIII Specially designed structures damaged slightly, others collapse. IX All buildings considerably damaged, many shift off foundations. Noticeable cracks in the ground. X Many structures destroyed. Ground badly cracked. XI Almost all structures fall. Bridges wrecked. XII Total destruction. Waves seen on ground surfaces.

25 Mercalli Scale – Level XI October 17th, 1985: San Francisco, USAExample… Mercalli Scale – Level XI Jan. 17th, 1995: Kobe, Japan October 17th, 1985: San Francisco, USA Jan. 17th, 1995: Kobe, Japan Level XI Almost all structures fall Bridges wrecked