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Earthquakes, Focus, Epicentre, Magnitude, Richter Scale, MMS, Mercalli Scale, Seismometer, Liquefaction, Landslides, Tsunamis, Waves
Earthquake
A violent shaking of the earth’s crust
Where do most earthquakes happen?
About 90% of earthquakes occur at plate boundaries and 10% intraplate
Which plate boundaries do the most destructive earthquakes occur?
Destructive and conservative
Intraplate
Relating to or occurring within the interior of a tectonic plate
How many earthquakes does the UK experience per year?
Estimated to be between 20 and 30
Why does the UK experience earthquakes when it is not on a plate boundary?
The UK lies on many ancient fault lines
What process have earthquakes recently been associated with?
Fracking
Focus
Where the plates move underground
Epicentre
The point on the surface straight above the focus
Trick to remember the difference between focus and epicentre
F is after E in the alphabet, so the focus in underground
What are the distance ranges from the surface of shallow, intermediate and deep focus?
Shallow focus: 0-70km deep
Intermediate focus: 70-300km deep
Deep focus: 300-700km deep
What is a primary seismic hazard?
Shockwaves, leading to the ground shaking
What are secondary seismic hazards?
Tsunamis
Liquefaction
Landslides
What is the Richter Scale?
A logarithmic scale which represents the magnitude of an earthquake
Each increase in the scale is 10x stronger than the previous
What is the difference between the Richter Scale and the Moment Magnitude Scale (MMS)
The MMS is the same as the Richter Scale (1-10) but uses more complex maths to calculate the total energy released
The Mercalli Scale
Measured 1-12 (Roman numerals)
Measures intensity and impact of an event
Subjective
Seismic Waves (Shockwaves)
Movements of energy that travel out from the focus of an earthquake
What are the two main types of seismic waves?
Body waves
Surface waves
What is the difference between body waves and surface waves?
Body waves travel through the earth
Surface waves travel along the earth’s surface
What are the two types of body wave?
Primary waves (P waves)
Secondary waves (S waves)
What speeds do P and S waves travel at?
P waves travel at approx. 20,000km/h
S waves travel at approx 10,000km/h
What are the two types of surface waves?
Rayleigh waves (up and down)
Love waves (sideways)
Outline the process of liquefaction
The space between the grains of soil contains air and water. Liquefaction is when, during an earthquake, the shaking causes particles of soil to clump together, which forces water quickly to rise upwards because the water is less dense than the soil. As the water breaks through to the surface it floods large areas with a wet sticky sludge.
What does soil contain?
Minerals
Organic matter (dead plants and animals)
Living organisms
Air
Water
Explain how earthquakes can lead to landslides
Strong earthquake ground shaking greatly increases the likelihood of landslides where landscape is susceptible to these types of ground failure. If the ground is saturated with water, particularly following heavy rainfall, the shaking will result in more landslides than normal.
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