Earthquakes and Seismic Waves Flashcards
Where and why do earthquakes happen?
95% of Earthquakes occur along Tectonic plate boundaries. When the plates move against each other, they sometimes stick causing huge amounts of pressure to build up. When the pressure becomes too much, the rock fractures along cracks called faults, and energy is suddenly released as seismic waves.
Features of an earthquake
Focus/hypocentre
Fault
epientre
seismic waves
tectonic plates
How does the depth of he focus/hypocentre influence the impacts of an earthquake.
Shallower= more impact on surface
Deeper=Less impact
What is the difference between surface waves and body waves?
Body waves travel through the earth itself whereas surface waves only travel along the surface.
Primary Waves (Body Waves)
The fastest waves
Can travel through both solids and liquids including rock such as granite at 5.5km/sec.
They travel in a back and forth motion.
Secondary Waves (Body Waves)
Slower than P Waves, travelling at 3km/sec through granite.
Can only travel through solids.
They move and and down or side to side.
Why are Surface Waves slower?
Surface waves are long waves so they take more time to complete one cycle of motion.
Love Waves
Faster than Rayleigh waves
Only travel through solids
Shake the ground at right angles in the direction of movement.
Larger and focus all energy on the Earth’s surface.
Horizontal Movement.
Rayleigh Waves
Only travel through solids
Focus all energy on the Earth’s surface.
Spread the furthest from the focus.
The ground moves in an elliptical pattern.
Responsible for most of the shaking felt by people.
How damaging are all the different types of waves and why?
Primary Waves are weak and don’t have the ability to interact with the Earth’s surface.
Secondary Waves are more likely to cause ground movement and building collapse.
Surfaces waves are the worst causing large scale damage.
What instrument is used to measure seismic waves?
Seismograph
What information can scientists get from seismic waves?
Amount of energy released.
Primary Effects of Seismic waves
Ground Shaking - leading to infrastructure collapse.
Crustal fracturing.
Secondary effects of Seismic waves
Avalanches and landslides - ground shaking may put pressure on slopes.
Tsunami - from underwater earthquake
Liquefaction- Violent shaking causes rocks to lose strength and become more liquid than solid. The subsoil loses its ability to to support building foundations so buildings and roads tilt or sink.
Case Study supporting secondary effects of Seismic waves
Kashmir 2005 (Landslides)
7.5 magnitude earthquake
epicentre near Muzafarrabad + Balaot in Pakistan
Followed by mudslides . More than 32000 buildings collapsed and 7900 fatalities.
Christchurch 2011Liquefaction
6.2 magnitude earthquake
69000 residential buildings collapsed
185 fatalities
