EAE 10 Disasters

Question 1

What are natural hazards?

Answer 1

Natural hazards are Dangers to organisms that are driven or induced through mainly tectonic forces on a dynamic plate.

• A hazard is a potential danger that, if it unfolds and affects humans, can become a disaster
• A natural hazard is driven by the environment around us, often plate tectonic forces or natural weather phenomena.
• These events occur whether we are here or not

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Question 2

What are natural disasters?

Answer 2

Natural disasters are Impacts on organisms (mainly humans) when a danger becomes reality.

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Question 3

What are man made hazards?

Answer 3

Man-made hazards are driven or accelerated by human activity.

Often man-made hazards relate to a natural phenomenon but are dangerous by direct or indirect action / influence

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Question 4

What is the impact of a disaster?

Answer 4

The impactof a disaster is related to magnitude (how big) and frequency (how often).

Actual damage depends on other factors too, such as population density, land-use, local geology etc.

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Question 5

What is a catastrophic event?

Answer 5

Immense damage → recovery and rehabilitation is a long process

e.g., New Orleans has still not recovered now, 10 years after the Hurricane

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Question 6

Frequency of New Zealand Earthquakes

Magnitude 4.0 -4.9

Answer 6

Approx 1 per day

Annual average of 352.05 per year

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Question 7

Frequency of New Zealand Earthquakes

Magnitude 5.0 -5.9

Answer 7

Approx 2 per month

Annual average of 27.26 per year

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Question 8

Frequency of New Zealand Earthquakes

Magnitude 6.0 -6.9

Answer 8

Approx 3 per 2 years

Annual average of 1.63 per year

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Question 9

Frequency of New Zealand Earthquakes

Magnitude 7.0 -7.9

Answer 9

Approx 1 per 4 years

Annual average of 0.26 per year

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Question 10

Frequency of New Zealand Earthquakes

Magnitude 8.0 or over

Answer 10

Approx 1 per century

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Question 11

How long does an Earthquake last?

Answer 11

An Earthquake is usually defined by a mainshock and followed by multiple aftershocks

Aftershocks become exponentially less after the main event.

The mainshockusually lasts 15-30 Seconds

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Question 12

What is Seismology?

Answer 12

The underlying science of Earthquakes and its hazards is seismology Seismology is the scientific study of earthquakes and the propagation of elastic waves

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Question 13

What are seismic waves?

Answer 13

Seismic waves are the waves of energy caused by the sudden breaking of rock within the Earth (or an explosion).

They are the energy that travels through the Earth and which is recorded on seismographs.

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Question 14

What are the types of seismic waves?

4 types.

Answer 14

Internal waves are:

• Primary (P) waves
• Secondary (S) waves

Surface waves are:

• Love (L) waves
• Rayleigh (R) waves

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Question 15

What are P waves

3 points.

Answer 15

• Primary waves (P) are the first to arrive.
• They move the crust like a concertina.
• These cause only moderate damage.

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Question 16

What are S waves

3 points.

Answer 16

• Secondary waves (S) arrive afterwards
• They move the earth up and down.
• They are destructive waves

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Question 17

Describe surface waves

3 points.

Answer 17

• Surface waves are the last ones to arrive.
• These get considerably weaker away from the epicenter.
• Surface waves are the most destructive waves

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Question 18

What type of wave is this?

Answer 18

Rayleigh (R) wave

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Question 19

What type of wave is this?

Answer 19

Love (L) wave

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Question 20

What is a fault zone?

Answer 20

A fault is a weak zone separating two geological blocks

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Question 21

How do earthquakes occur?

5 points.

Answer 21

• Earthquakes occur through sudden thrust, often related to fault zones.
• Tectonic forces cause the blocks to move relative to each other.
• When the movement is not linear, but occurs in sudden bursts, an earthquake occurs.
• Built-up energy is released.
• This occurs when stress overcomes friction

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Question 22

What does the S-P interval tell us?

Answer 22

The S-P interval tells the seismologist how far away the earthquake was.

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Question 23

What is the moment magnitude scale?

Answer 23

The moment magnitude scale (often called Richter Scale) is a measure for the energy released by an Earthquake or how strong an earthquake is.

⇒ The scale (or magnitude) is governed by amplitude and distance (equals travel time)!

⇒ The scale is logarithmic.

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Question 24

Where is the epicenter?

5 points.

Answer 24

• The epicentre of an Earthquake is the vertical projection of the center of the energy at depth towards the surface.
• It can usually be traced through multiple stations collecting wave amplitude and runtimes.
• The epicentre is not always related to the fault zone at the surface!
• Surface waves arrive fastest at the epicenter. From there they get weaker.
• That is why the epicenter is usually hit the hardest

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Question 25

Earthquakes at convergent plate boundaries

5 points.

Answer 25

• Pressure can build up when two plates collide. This convergence can result in a collisional orogeny (like the Himalayas) or subduction zones (like the Marianas Arc)
• Oceanic crust is denser than continental crust and will subduct.
• Older (cooler crust) is denser than younger (hotter) crust and will subduct.
• In the process of subduction, slabs often slide into the mantle, often in pulses. Plates can be interlocked and a sudden release (thrust) and this movement causes earthquakes.
• This can cause megathrust Earthquakes (M > 9)

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Question 26

What is liquefaction?

3 points.

Answer 26

Liquefaction is a phenomenon in which the strength and stiffnessof a soil is reduced by earthquake shaking or other rapid loading.

• Liquefactionand related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world.
• When the Earth”shakes” or moves rapidly, lose grains will also move and redistribute. If these sediments have a larger porosity, and liquid in inter-porous space, liquids can move towards the surface. Soil can behave like liquid.
• Anything that was build on top of this, will lose its foundation.

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Question 27

What are the earthquake hazards?

5 points.

Answer 27

• Most lethal damage is done through collapsing buildings and infrastructure
• Often additional deaths can occur through aftershocks in unstable buildings and already damaged structures
• Liquefaction can cause serious damage.
• Secondary hazards e.g. loss of infrastructure and other events
• Policies include building code, emergency response and knowing your geology.

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Question 28

What are the secondary hazards of earthquakes?

5 points.

Answer 28

• Loss of infrastructure such as water, electricity and housing.
• Landslides
• Tsunamis or flooding
• Volcanic eruptions
• Fires

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