HAZARDS 5 - Earthquakes and Tsunamis Flashcards
What are primary waves?
Waves that are fastest and reach the surface first
What are secondary waves?
Waves that are half as fast as primary waves and reach the surface second
What’s a tsunami?
Waves generated from activity on the ocean floor
What is the epicentre?
The point on the surface directly above the focus
What is the focus?
The breaking point of the earthquake within the lithosphere
What are the characteristics of primary waves?
- perpendicular to the Earths surface
- high frequency
- fast + reach the surface fast
- travel through mantle and core (solids + liquids) > move in different ways and speeds
- radiate through the Earth - shadow zones
What are the characteristics of secondary waves?
- move buildings slide to slide
- higher frequency but slower
- can only move through the mantle (liquid) > shadow zones
What are Rayleigh waves?
Radiate from the centre from the epicentre in low > frequency rolling motions
What are Surface Love waves?
- slowest waves
- cause the most damage
What are the lowest (1) and highest (4) types of earthquakes within an increased likelihood of a large magnitude?
- Constructive
- narrow belt + shallow focus - Collusion
- wide belt of mostly shallow focus (some intermediate) - Conservative
- shallow focus, narrow belt, intermediate to high magnitude > less frequent - Destructive
- fairly wide belt of increasing focal depth away from the boundary > strongest magnitude
What are the two measures of Earthquakes?
- Modified Mercalli Scale
- Richter Scale
What does the Modified Mercalli Scale entail?
- looks at the damage caused
- observations
- twelve point scale (imperceptible to catastrophic)
- subjective + based perception
What does the Richter scale entail?
- 1-8 logarithmic scale
- objective and quantitative
How are tsunamis formed?
- plates slip
- one pushes a large mass of water up
- water rotates and causes a tsunami
What are the characteristics of a tsunami?
- low wave until they reach the shore (can exceed 25m high)
- long wave length (100-1000km)
- 640-960km/h
- series of waves
- 10-60m between each wave
What are some of the ways of mitigating against earthquakes?
- Computer controlled weights on the roof
- Steel frames which sway during earth movements
- Automatic windows shutters to prevent falling glass
- Open areas where people can assemble if evacuated
- Foundations sunk into bedrock avoiding clay
- ‘Bird-cage’ interlocking steel frame
- Outer panels flexibly attached to steel structure
- Roads to provide quick access for emergency services
- Rubber shock absorbers to absorb earth tremors
What are some warning signs of Earthquakes?
- Microquakes before the main tremor
- Bulging of the ground
- Decr radon gas concentration in the ground water
- Raised groundwater levels
- Electrical + magnetic changes within local rocks
- Incr argon gas content in the soil
- Curious animal behaviour
What is liquefaction?
- a jelly-like state of silts and clays resulting from intense ground shaking
- may result in subsidence and collapse of buildings following an earthquake
What is the concept of liquefaction?
- when compacted sediment loses strength and fitness in response to an applied force
- soil saturation, loses and sandy at most risk
- loses strength and structure > flows like a liquid
- can cause buildings and infrastructure to collapse > risk to life as acts as quick sand
What is the multiplier effect?
The ‘snowballing’ of economic activity (pos or neg)
What are some of the factors influencing impacts of seismic activity?
- Magnitude + depth of Earthquake
- Distance from the epicentre
- Geological conditions
- Population density, preparedness and eduction
- Design + strength of buildings
- Time of day
- Impact of indirect hazards such as fires, landslides and tsunamis
What are some examples of primary effects?
- shaking ground causes damage to infrastructure e.g. power lines + roads
- schools, colleges, unis destroyed
- immediate deaths
- destruction of housing
- slope failure + liquefaction
- panic, fear, hunger
What are some examples of secondary effects?
- emergency services hindered + fires from broken power lines
- lack of education while infrastructure rebuilt
- decr workforce + treatment for injuries
- displaced + NGOs provide tents, water + aid
- loss of housing and destruction of land
- looting + public disorder
What are some examples of long term impacts?
- repair + construction (depends on levels of development)
- reduction of skills + potential unemployment
- psychological issues + decr economic output
- reconstruction to get people out of temporary housing
- need to rebuild + potentially relocation
- restore order (lack of gov power)
