Earthquakes Flashcards
How do earthquakes actually occur?
When the tectonic plates move against each other at plate boundaries they sometimes stick.
Intense pressure builds up until it becomes too much and the crust fractures along cracks called faults.
The point of fracture is called the focus and it is from here that energy is suddenly released as seismic waves. These waves radiate out from the focus; they shake the ground most violently at the point directly above the focus- the epicentre.
What are body waves
Waves that trevel through earth’s body. Includes P waves and S waves.
What are P waves (primary or pressure)?
Fastest waves.
First to reach surface.
Travel through solids and liquids.
Push through the crust.
What are S waves (secondary or shear)?
60% slower than P waves.
Travel through solids.
Move crust up and down.
More damaging than P waves.
What are love waves?
Fastest surface wave.
Move crust from side to side.
Largest waves; cause most damage.
What are rayleigh waves?
Last wave to arrive.
Travel through surface of the crust with a rolling motion so move the crust up and down like an S wave.
How can earthquakes be measured?
Magnitude and intensity
What is used to measure the magnitude of an earthquake?
A seismometer on the Richter scale.
What is used to measure intensity?
Measured using observations on the Mercalli Intensity Scale I-XII
What does ground shaking cause?
Buildings, bridges, roads and infrastructure to collapse- killing or injuring those nearby.
How is a tsunami caused in terms of earthquakes?
Submarine earthquakes can displace water leading to a tsunami.
What is liquefaction?
The violent shaking during an earthquake causes surface rocks to lose strength and become more liquid than solid.
The ground loses its ability to support weigh so buildings and roads tilt or sink.
How if fire caused?
Underground power lines and gas pipes and be severed leading to fire.
What is crustal fracturing?
Seismic energy causes the earth’s crust to crack at the surface.
How are landslides and avalanches caused?
Ground shaking places stress on slopes which can cause them to fail resulting in landslides, mudslides, rock falls and avalanches.
