2.1 Seismic hazards (and mutlihazard environment) Flashcards
Define an earthquake
A sudden violet shaking of the ground
Why do earthquakes happen
As plates move around the earths crust, stress builds up. When this stress is released, violent shaking occurs
Which 2 things effect an earthquakes magnitude
Focus - point of pressure release
Epicentre - immediately above focus on earths surface
What is the difference between a deep and a shallow focus
Shallow focus (0-70km) causes most damage
Deep focus causes least damage because the waves lose energy as they travel
What are the 2 types of seismic waves
Primary waves (Fast, vertical, liquids and solids)
Secondary waves (Slow, horizontal, liquids, most destructive)
Where do most earthquakes occur
Along destructive margins (80% and most destructive)
Conservative plate margins (movement along a fault)
Why do some earthquakes occur away from plate margins
Human activity or the reactivation of old fault lines
What 3 scales can we use to measure the magnitude of an earthquake
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
How can we measure the frequency of an earthquake
Seismic records
Historical records (1848 prior)
How does a seismograph work
Seismographs measure the amplitude of seismic waves through CONVERTING VIBRATIONS INTO ELECTRIC SIGNALS which are then put onto a graph
What are the primary effects of earthquakes
Ground shaking
Ground rupture
What are the secondary effects of earthquakes
Aftershocks
Landslides
Fires
Liquefaction
Tsunamis
What is liquefaction and how does it occur
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
What are tsunamis and what 2 ways can they form
Tsunamis are large waves caused by the displacement of a large volume of water
Earthquakes
Landslides
How are tsunamis formed by ocean earthquakes
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.
Give an example of 2 tsunami case studies
The Indian Ocean Tsunami
Tohoku, Japan Tsunami (multi hazardous environment)
Give some context for the Indian Ocean tsunami
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
What were the primary and secondary physical effects of the Indian Ocean earthquakes
Ground shaking
Tsunami (20m high)
What were the primary human impact of the Indian Ocean tsunami
$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
What were the secondary human impact of the Indian Ocean tsunami
Aid was slow due to destroyed infrastructure
Tourism severely effected
What were the primary responses for the Indian Ocean tsunami
Warnings given out far too late
160 aid organisation gave relief and foreign military helped out
What were the secondary responses for the Indian Ocean tsunami
Political barriers slowed aid
Government ignored underclass
Tourist areas quickly rebuilt
Tsunami warning systems put in place
Education and awareness
Give some context for the Tohoku tsunami
Occurred March 2011
Magnitude 9 earthquake occurred when North American plate slipped 5-10m upwards
What were the primary and secondary physical effects of the Tohoku earthquakes
Earth axis shifted 10cm
Made earth days 1 microsecond shorter
Tsunami wave(10m high)
700 aftershocks
What were the primary human impact of the Tohoku earthquake
Infrastructure devastated
18,000 dead
500,000 homeless
500km area flooded
Buildings “shaking like trees”
What were the primary human responses of the Tohoku earthquake
100,000 soldiers mobilised
63 search and rescue specialists (UK)
No looting or violence
What were the secondary human responses of the Tohoku earthquake
Upgraded tsunami warning system 2 years later
Relaxed planning and tax regulations to encourage new growth
What is a multi hazardous environment
A place where a number of physical hazards combine to create an increased risk
What makes Japan a multi hazardous environment
111 active volcanos
1/3 of earths quakes(4 plate boundaries)
Lies in path of tropical cyclone activity
Vulnerable to flooding, landslides etc
Why do people live in multi-hazardous environments
- Sense of place
- Seen as resources
Where the people of Japan vulnerable to the Tohoku earthquake
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
