Seismic Hazards Flashcards
What is the nature of seismicity in relation to plate tectonics?
The movement of plate tectonics causes pressure to build up in the lithosphere.
When pressure is released a series of tremors known as earthquakes occcur - this is why 90% of earthquakes occur at plate margins.
What is the epicentre of an earthquake?
The point on the earth’s surface where the earthquake is felt first - directly above the focus that usually experiences the most intense ground shaking.
What is the focus of an earthquake?
A point for example a fault line that shockwaves spread out from.
Near the focus waves are stronger and cause more damage
What are body waves?
Shockwaves that travel through the earth - there are two types. Primary and secondary.
What are primary (P) waves?
travel through both liquids and solids and are the fastest waves, reaching the surface first
They can travel through both the crust, mantle and the core to the opposite side of the Earth. There are compressional waves, which means that they compress and expand any material they pass through.
What are secondary (S) waves?
travel through the Earth, but unlike primary waves, they cannot travel through solids such as the core. They are half as fast as primary waves and are transverse waves. This means that they shake the ground at right angles to the direction of the wave (up and down).
What are surface waves?
Travel along the Earth’s surface.
Because they cannot travel through the mantle and core, they arrive later than body waves.
Two types - Love waves and Rayleigh waves.
What are love (L) waves?
are the slowest waves but they are the most destructive.
They shake the ground from side to side, which can damage infrastructure and buildings.
What are Rayleigh (R) waves?
travel out from the epicentre near the surface. The move in a rolling motion, like the swell of ocean waves. They can break up the surface.
Tsunamis
Are large waves caused by displacement of large volumes of water
Can be triggered by underwater earthquakes which cause the seabed to move, displacing water.
The greater movement of sea floor the larger the volume of water displaced and the bigger the wave produced.
They have long wave length and low wave height
Travel quickly
More powerful close to coast - waves lose energy as they travel towards land.
Landslides and avalanches
Shaking of ground can dislodge rock, soil, snow causing landslides and avalanches that move downslope quickly.
Shaking can also loosen ground material, making it easier for water to infiltrate. The weight of the water can trigger landslides.
Soil liquefaction
When soil is saturated with water, the vibrations of an earthquake can cause it to act like liquid.
This makes soil weaker and easier to deform, more likely to subside
What are the social impacts of seismic events?
Can cause buildings to collapse, killing and injuring people
Lack of clean water - can cause disease to spread
Tsunamis can flood areas, killing people and causing widespread damage to property.
What are environmental impacts of seismic events?
Tsunamis flood freshwater ecosystems, killing plants and animals
Fires started by damaged gas and electricity lines can destroy ecosystems
Damaged industrial units - leak chemicals/ radioactive material that damage ecosystems
What are economic impacts of seismic events?
Destroy business premises - damages economy of region
Damage to buildings and infrastructure can be very expensive to repair
