Seismicity

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  • Created by: Evie :)
  • Created on: 18-11-21 19:06
What is an earthquake?
A release of pressure at the earths surface which results in an intense shaking motion
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How many earthquakes occur each year?
The earth rumbles, twitches, jolts and shakes thousands of times a year
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How many earthquakes occur in the UK?
300 earthquakes are experienced annually
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How many people are killed by earthquakes per year?
63,000 people
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What is the global pattern of earthquakes?
130 magnitude 6 earthquakes per year
15 magnitude 7 earthquakes per year

Greatest concentration at destructive margins (around the pacific)
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What is the focus and epicentre of an earthquake
Focus: Where pressure is released
Epicentre: The point on the surface immediately above the focus
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Classifications

Shallow focus earthquake facts
- focus depth of 0-70km
- Tend to cause the most damage at the surface
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Intermediate focus earthquake facts
Focus depth of 70-300km
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deep focus earthquake facts
Focus depth of 300-700km deep
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Constructive margin and earthquake classification relationship
Shallow focus earthquakes, due to tensional forces in the crust
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Destructive margin and earthquake classification relationship
Deep focus earthquakes located where the crust melts in the benioff zone
Shallow focus earthquakes occur at the point of subduction
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Conservative margins and earthquake classification relationship
Shallow focus earthquakes occur as pressure is released in plates sliding past each other
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What are the two types of seismic shock waves?
Body waves(P and S)
Surface waves(L and R)
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Body waves:
Characteristics of P (primary) waves
-Compressional waves/ they are fast and reach the surface first
- They move at approx 5.5km/s
- They travel through liquids and solids
- They form compressions as they push through the crust, mantle and core
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What is happening with a P wave
They compress and expand the material they pass through, which forces rocks to move back and forward and cause the ground to break up.
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Body waves:
Characteristics of S(surface) waves
- Shear waves
-Travel at half the speed of P waves (approx 3km/s) and reach the surface after P waves
- They only travel through solids
- They travel through the crust and upper mantle only
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What is happening with an S wave
They cause material to shake at right angles to the direction of wave motion, causing the ground to shake up and down.
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Characteristics of L(love) waves and R (Rayleigh) waves
L= Slowest most damaging waves
R= Slow waves, which travel at around 300m/s through the ground or 3km/s in test scenarios.
They are less damaging than L waves
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Surface waves:
What is happening with an L wave
They shake the ground side to side
Causes damage to infrastructure and buildings
Can pass through solids only
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Surface waves:
What is happening with an R wave
- Moves the ground similarly to waves in the sea(rolling motion)
- Can pass through solids only
- Amplitude of wave diminishes with depth below the surface
- Underlying geology of an area can affect the way in which surface waves travel(effects will be wo
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Other cards in this set

Card 2

Front

How many earthquakes occur each year?

Back

The earth rumbles, twitches, jolts and shakes thousands of times a year

Card 3

Front

How many earthquakes occur in the UK?

Back

Preview of the front of card 3

Card 4

Front

How many people are killed by earthquakes per year?

Back

Preview of the front of card 4

Card 5

Front

What is the global pattern of earthquakes?

Back

Preview of the front of card 5
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