2.1 Seismic hazards (and mutlihazard environment)

Question 1

Define an earthquake

Answer 1

A sudden violet shaking of the ground

Question 2

Why do earthquakes happen

Answer 2

As plates move around the earths crust, stress builds up. When this stress is released, violent shaking occurs

Question 3

Which 2 things effect an earthquakes magnitude

Answer 3

Focus - point of pressure release

Epicentre - immediately above focus on earths surface

Question 4

What is the difference between a deep and a shallow focus

Answer 4

Shallow focus (0-70km) causes most damage

Deep focus causes least damage because the waves lose energy as they travel

Question 5

What are the 2 types of seismic waves

Answer 5

Primary waves (Fast, vertical, liquids and solids)

Secondary waves (Slow, horizontal, liquids, most destructive)

Question 6

Where do most earthquakes occur

Answer 6

Along destructive margins (80% and most destructive)

Conservative plate margins (movement along a fault)

Question 7

Why do some earthquakes occur away from plate margins

Answer 7

Human activity or the reactivation of old fault lines

Question 8

What 3 scales can we use to measure the magnitude of an earthquake

Answer 8

Richter scale (scale from 1-10, measures energy released and amplitude)

MM scale (More accurate version of Richter scale which measures energy released

Mercalli scale (scale from 1-12, measures impact of event from ground obserations

Question 9

How can we measure the frequency of an earthquake

Answer 9

Seismic records
Historical records (1848 prior)

Question 10

How does a seismograph work

Answer 10

Seismographs measure the amplitude of seismic waves through CONVERTING VIBRATIONS INTO ELECTRIC SIGNALS which are then put onto a graph

Question 11

What are the primary effects of earthquakes

Answer 11

Ground shaking
Ground rupture

Question 12

What are the secondary effects of earthquakes

Answer 12

Aftershocks
Landslides
Fires
Liquefaction
Tsunamis

Question 13

What is liquefaction and how does it occur

Answer 13

When SATURATED SOILS behave like liquid

Vibrations in the ground cause particles to undergo stress, causing them to lose structure and behave like a liquid. This means they can’t withstand their own weight and everything above collapses

Question 14

What are tsunamis and what 2 ways can they form

Answer 14

Tsunamis are large waves caused by the displacement of a large volume of water

Earthquakes
Landslides

Question 15

How are tsunamis formed by ocean earthquakes

Answer 15

Earthquakes can result in the sudden rise or fall of the earths crust. This energy causes the water above to rise and fall, creating tsunami waves, which at first are not very high

As they reach shallow water, the waves become compressed and their energy becomes concentrated , with wavelength decreasing and wave height increasing.

Question 16

Give an example of 2 tsunami case studies

Answer 16

The Indian Ocean Tsunami
Tohoku, Japan Tsunami (multi hazardous environment)

Question 17

Give some context for the Indian Ocean tsunami

Answer 17

Occurred Boxing Day 2004.

A 9.3 magnitude earthquake displaced kilometres of seabed by 15m near Indonesia

It spread to 12 countries, with Indonesia being the worst effected, and even reaching east Africa

Question 18

What were the primary and secondary physical effects of the Indian Ocean earthquakes

Answer 18

Ground shaking

Tsunami (20m high)

Question 19

What were the primary human impact of the Indian Ocean tsunami

Answer 19

$10 billion in material losses

230,000 deaths (pretty much all of them due to the tsunami)
500,000 in refugee camps

Coastal settlements devastated

Question 20

What were the secondary human impact of the Indian Ocean tsunami

Answer 20

Aid was slow due to destroyed infrastructure

Tourism severely effected

Question 21

What were the primary responses for the Indian Ocean tsunami

Answer 21

Warnings given out far too late

160 aid organisation gave relief and foreign military helped out

Question 22

What were the secondary responses for the Indian Ocean tsunami

Answer 22

Political barriers slowed aid
Government ignored underclass
Tourist areas quickly rebuilt
Tsunami warning systems put in place
Education and awareness

Question 23

Give some context for the Tohoku tsunami

Answer 23

Occurred March 2011

Magnitude 9 earthquake occurred when North American plate slipped 5-10m upwards

Question 24

What were the primary and secondary physical effects of the Tohoku earthquakes

Answer 24

Earth axis shifted 10cm
Made earth days 1 microsecond shorter

Tsunami wave(10m high)
700 aftershocks

Question 25

What were the primary human impact of the Tohoku earthquake

Answer 25

Infrastructure devastated

18,000 dead
500,000 homeless

500km area flooded
Buildings “shaking like trees”

Question 26

What were the primary human responses of the Tohoku earthquake

Answer 26

100,000 soldiers mobilised
63 search and rescue specialists (UK)
No looting or violence

Question 27

What were the secondary human responses of the Tohoku earthquake

Answer 27

Upgraded tsunami warning system 2 years later

Relaxed planning and tax regulations to encourage new growth

Question 28

What is a multi hazardous environment

Answer 28

A place where a number of physical hazards combine to create an increased risk

Question 29

What makes Japan a multi hazardous environment

Answer 29

111 active volcanos
1/3 of earths quakes(4 plate boundaries)
Lies in path of tropical cyclone activity
Vulnerable to flooding, landslides etc

Question 30

Why do people live in multi-hazardous environments

Answer 30

1. Sense of place
2. Seen as resources

Question 31

Where the people of Japan vulnerable to the Tohoku earthquake

Answer 31

Initially no, Japan are well equipped to deal with hazards and have adapted great human deterrents such as their retrofitted buildings.

However, the tsunami is what made them vulnerable