5.9 earthquakes and tsunamis

  1. In general terms what is seismicity?

How frequent earthquakes are in an area

  1. What are the natural causes of seismic activity?

Movement of tectonic plates along the plate boundaries which can cause movement of the land as well as tectonic activity

  1. Are there any human causes of seismic activity?

Mining, fracking and oil extraction

  1. Define the term ‘epicentre’?

The area in the surface of the earth directly above the focus of the earthquake

  1. What is the focus?

The centre in the ground where the earthquake starts from

  1. Use the table below to describe the different types of waves/

Wave name

Shape

Effect/notes

P

Push through crust, mantle and core

High frequency through the earth

S

Shake through crust and mantle

Don’t travel through earth, high frequency

L

Side to side

Slowest, cause most damage

R

Up and down

Radiate from epicentre, low frequency rolling

 

Tsunamis

  1. Summarize the paragraph on page 235 about Tsunamis.

Generated by seismic activity underwater like volcanoes and earthquakes

Can also be caused by underwater landslides and asteroid strikes

Wave height starts low but grows when reaching the shore

Long wavelength of 100-1000km

Very fast 640-960km/hr

Long time between each wave 10-60 mins

When approaching coast it can build up into a wall

90% around the ring of fire

Influenced by population density, coastal relief and land use by the coast

Pacific Tsunami Warning System in Hawaii alerts hours in advance after major seismic events

The sea draining is often the first sign

  1. Using fig 3 on P235 and extra notes explain how a tsunami increases in high and effect as it hits the coast?

Long wavelength out at sea but low wave height, but the wave, as it comes towards the coast, the wave slows and the water all piles up and the wavelength shrinks which creates a giant wave.

 

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