EAE 10 Disasters Flashcards
What are natural hazards?
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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What are natural disasters?
Natural disasters are Impacts on organisms (mainly humans) when a danger becomes reality.
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What are man made hazards?
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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What is the impact of a disaster?
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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What is a catastrophic event?
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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Frequency of New Zealand Earthquakes
Magnitude 4.0 -4.9
Approx 1 per day
Annual average of 352.05 per year
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Frequency of New Zealand Earthquakes
Magnitude 5.0 -5.9
Approx 2 per month
Annual average of 27.26 per year
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Frequency of New Zealand Earthquakes
Magnitude 6.0 -6.9
Approx 3 per 2 years
Annual average of 1.63 per year
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Frequency of New Zealand Earthquakes
Magnitude 7.0 -7.9
Approx 1 per 4 years
Annual average of 0.26 per year
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Frequency of New Zealand Earthquakes
Magnitude 8.0 or over
Approx 1 per century
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How long does an Earthquake last?
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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What is Seismology?
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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What are seismic waves?
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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What are the types of seismic waves?
4 types.
Internal waves are:
- Primary (P) waves
- Secondary (S) waves
Surface waves are:
- Love (L) waves
- Rayleigh (R) waves
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What are P waves
3 points.
- Primary waves (P) are the first to arrive.
- They move the crust like a concertina.
- These cause only moderate damage.
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What are S waves
3 points.
- Secondary waves (S) arrive afterwards
- They move the earth up and down.
- They are destructive waves
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Describe surface waves
3 points.
- 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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What type of wave is this?
Rayleigh (R) wave
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What type of wave is this?
Love (L) wave
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What is a fault zone?
A fault is a weak zone separating two geological blocks
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How do earthquakes occur?
5 points.
- 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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What does the S-P interval tell us?
The S-P interval tells the seismologist how far away the earthquake was.
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What is the moment magnitude scale?
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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Where is the epicenter?
5 points.
- 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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Earthquakes at convergent plate boundaries
5 points.
- 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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What is liquefaction?
3 points.
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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What are the earthquake hazards?
5 points.
- 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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What are the secondary hazards of earthquakes?
5 points.
- Loss of infrastructure such as water, electricity and housing.
- Landslides
- Tsunamis or flooding
- Volcanic eruptions
- Fires
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