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Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

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Page 1: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Seismic Events

Causes of EarthquakesDistribution of EarthquakesMeasuring EarthquakesThe Effects of Earthquakes

Page 2: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

WHAT IS AN EARTHQUAKE?

•Sudden release of energy

•Creates seismic waves (similar to waves through water)

•Waves spread out spherically

•Greatest damage occurs at the epicentre

Page 3: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

P & S waves

• Two types of wave explained.

• Circle of power demonstration.

• P & S travel through the interior of the earth – out from the epicentre.

Page 4: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

P-waves

• P waves (primary waves) are compressional waves.

• In solids, these waves generally travel almost twice as fast as S waves.

• P waves can travel through any type of material. • In air, these pressure waves take the form of

sound waves.• They travel at are 330 m/s in air, 1450 m/s in

water and about 5000 m/s in granite. (m/s = meters per second.)

Page 5: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

PRIMARY WAVE ‘p-wave’

– Longitudinal– Sudden jolt felt as the quake hits.

Page 6: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

S waves

• S waves (secondary waves) are transverse which means that the ground is displaced perpendicularly (sideways) to the direction of movement.

• The ground moves alternately to one side and then the other. (or up or down… depending on the direction of the wave.)

• S waves can travel only through solids, as fluids (liquids and gases)

• Their speed is about 60% of that of P waves in a given material.

• S waves arrive second in a seismic station because of their slower speed.

• They are sometimes called shear waves.

Page 7: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

SECONDARY WAVE ‘s-wave’

– Transverse (shake at right angles to the direction of the wave.)– Sustained shaking felt as quake hits

Page 8: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

L wave• The particle motion of a Love wave forms a horizontal line

perpendicular to the direction of movement (i.e. are transverse waves). • Since Love waves travel on the Earth's surface, the strength (or

amplitude) of the waves decrease exponentially with the depth of an earthquake.

• Surface waves therefore decay more slowly with distance than do body waves, which travel in three dimensions.

• Large earthquakes may generate Love waves that travel around the Earth several times before dissipating.

• Since they decay so slowly, Love waves are the most destructive outside the immediate area of the focus or epicentre of an earthquake. They are what most people feel directly during an earthquake.

Page 9: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

LOVE WAVE. L-wave

Page 10: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Lets get an overview.

Read the book pages 24 - 27

Worksheet– Sheet 5 & 6

Page 11: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Distribution of Earthquakes

• What is the distribution of Earthquakes?

• Read the section in the book then use following statements to make a short paragraph explaining the distribution of Earthquakes.

– The Pacific Ring of Fire– 70% of Earthquake and Volcanic activity is found around

it’s edges– Volcanoes and Earthquakes are frequent.– Represents the destructive plate boundaries around the

edges of the plate.

Page 12: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

THE RICHTER SCALE

•Invented by Charles Francis Richter in 1935

•Measure of an earthquake’s magnitude

•Scale between 0 and 10(theoretically)

•Logarithmic scale

Page 13: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

How does a seismograph work?

Measurement – using a seismograph http://www.wwnorton.com/college/geo/egeo/flash/8_3.swf

Magnitude: A measure of the size of an earthquake.Frequency: Is the number of occurrences of a repeating event per unit time.

Page 14: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

• Worksheet 1.10

Page 15: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Effects of an Earthquake

• National Geographic 4 min clip – the effects of earthquakes. Link

• The text book explains several effects– Liqufaction– Landslides/avalanches– Effects on built environment– Tsunamis

Page 16: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Liquefaction Explained

http://www.youtube.com/watch?v=PwvvYxSZ7PI

http://www.youtube.com/watch?v=sV2WeR670ls

Page 17: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

What happened in San Francisco?

Year 9 Worksheet 1.20. 1.21.

Page 18: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Aftershocks

A tremor (or one of a series of tremors) occurring after the main

shock of an earthquake : Video

Page 19: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Mass Movement when masses of rock, earth, or debris move down a slope.

• Mass movement is movement of masses of bodies of soil, bed rock, rock debris, soil, or mud.

• They may be very small or very large, and can move at slow to very high speeds.

• Usually occur along steep-sided hills and mountains because of the pull of gravity.

• An avalanche is a sudden flow of a large mass of snow or ice down a slope, sometimes at speeds exceeding 160 km/hr.

• Mass movement and avalanches can be started when earthquakes destabilise rock and start a slide.

• http://www.youtube.com/watch?v=JrV4uCVwmfk

Page 20: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Tsunami -

• What is a Tsunami?• Tsunami -a large wave, or series of

waves, caused when an earthquake causes massive undersea crust movements and/or collapses which displace the water above.

• Earthquakes deform the ocean floor, pushing the overlying water up into a tsunami wave.

Page 21: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes
Page 23: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Case study – Boxing Day Tsunami.

• Make a 5 point PowerPoint to get the key facts about the Tsunami across. Use case study on page 29 to help.– Why it occurred.– Where it started.– What it effected.– Positive side effects.

Page 24: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Plenary

Page 25: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Earthquakes don’t kill people, buildings do.

Page 26: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Starter

Earthquakes don’t kill people… BUILDINGS DO!!!

Page 27: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

Port-au-Prince, Haiti

Page 28: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

BUILDINGS• Side to side forces that cause collapse

• Damage caused by lateral forces

Page 29: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

• Building tilted due to first story building collapse

Page 30: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

HOW TO BUILDSMALL BUILDINGS

• Shear walls

• Concentrate the damage

• Cross Bracing• Reinforced stone wall

Page 31: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

• Cross bracing • Construction of Pearl River Tower, China

Page 32: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

LARGER BUILDINGS

• Base isolation

• Left: regular building Right: base isolated building

Page 33: Seismic Events Causes of Earthquakes Distribution of Earthquakes Measuring Earthquakes The Effects of Earthquakes

• Ways of improving resistance to earthquakes