1.1.4
Earthquakes
Overview of Earthquakes
Overview of Earthquakes
An earthquake is a sudden or violent movement within the Earth’s crust followed by a series of shocks. An earthquake happens when the Earth’s plates move and cause the ground to shake.
Terminology
Terminology
- The focus is where the pressure is released underground and where the energy radiates out from. This is the place with the strongest waves that cause the most damage.
- The epicentre is the point directly above the centre of the earthquake on the earth’s surface.
- Seismic waves are when energy is released from the focus in shock waves.
- The most damage will occur at the places where the shock waves are strongest (i.e. closest to the epicentre).
Caused by release of built up stress
Caused by release of built up stress
- The plates on the Earth’s crust are always moving and so tensions can build up between rocks.
- This stress can suddenly be released when the strain overcomes the elasticity of the rock.
- This release of stress can cause parts of the surface to experience an intense shaking motion that lasts for a few seconds.
Transfer of energy
Transfer of energy
- Large amounts of energy are released.
- Much of this energy is transferred vertically to the surface and then moves outwards from the epicentre (point on surface above the focus) as seismic waves
- After the moment of fracture, rocks may regain their original shape but in a new position.
Types of Earthquakes
Types of Earthquakes
Earthquakes happen at various depths and in various environments. The depth of focus (point below the surface where an earthquake occurs) of an earthquake is significant.
Shallow-focus earthquakes
Shallow-focus earthquakes
- Shallow-focus earthquakes are those where the focus is 0-70km under the Earth's surface.
Deep-focus earthquakes
Deep-focus earthquakes
- Deep-focus earthquakes are those where the focus is 70-700km under the Earth's surface.
- Deep-focus earthquakes are caused by previously subducted crust moving towards the core, heating up or decomposing.
- Deep-focus earthquakes are generally less damaging than shallow-focus because the shock waves have to travel further and so cause less shaking at the surface.
Underwater earthquakes
Underwater earthquakes
- Underwater earthquakes move the seabed, which causes water to get displaced. If enough water is displaced, tsunamis (series of enormous waves) can happen.
- Underwater earthquakes can be shallow- or deep-focus. The deeper the focus, the bigger the tsunami.
- Waves travel fast in deep water, and so tsunamis can strike shores with little warning. This can catch people off-guard and cause many deaths.
Earthquake Waves
Earthquake Waves
Earthquakes can create three different types of wave that have varying effects:
P-waves
P-waves
- An earthquake can produce P-waves (primary waves) when the tectonic stress energy is released.
- P-waves are the fastest waves but they cause the least damage.
S-waves
S-waves
- Some earthquakes produce S-waves (secondary waves) that make the ground shake violently.
L-waves
L-waves
- The waves that create significant damage, including crustal fracturing, are L-waves (Love waves).
- These waves only travel across the surface and have a large amplitude.
1Tectonic Processes & Hazards
1.1Tectonic Processes & Hazards
1.2Natural Disasters
1.3Natural Disaster Case Studies
1.4Trends & Patterns
2Option 2A: Glaciated Landscapes & Change
2.1Glaciated Landscapes Over Time
2.2Periglacial Landscapes
2.3Glacial Processes
2.4Glacial Landforms
3Option 2B: Coastal Landscapes & Change
3.1Coastal Landscapes
3.2Coastal Erosion & Deposition
3.3Coastal Risks
4Globalisation
4.1Globalisation
4.2Negatives of Globalisation
4.3Global Shift
4.5Culture
4.6Measuring Development
5Option 4A: Regenerating Places
5.1Types of Economies
5.2Function of Places
5.3Regeneration
5.4Regeneration Case Studies
6Option 4B: Diverse Places
6.1Population Structure
6.2Past & Present Connections
6.3Urban & Rural Spaces
6.4Diversity
6.5Urban & Rural Case Studies
6.6Case Study - Tower Hamlets
6.7Case Study - Sturton-le-Steeple
7The Water Cycle & Water Insecurity (A2 only)
7.1Hydrological Processes Global to Local
7.2Influences on the Water Cycle
7.3Water Insecurity
8The Carbon Cycle & Energy Security (A2 only)
8.1The Carbon Cycle
8.2Energy Consumption
8.3Alternative Energy
8.4Growing Demand for Resources
9Superpowers (A2 only)
9.1Superpowers
9.2Hard & Soft Power
9.2.1Hard & Soft Power
9.2.2Emerging Powers - China Rivalry
9.2.3Emerging Powers - Chinese Sources of Power
9.2.4Emerging Powers - Brazil
9.2.5Emerging Powers - Russia
9.2.6Emerging Powers - India
9.2.7Theories of Development
9.2.8Power Case Studies: Chinese One Belt One Road
9.2.9Power Case Studies: Pakistan Nuclear Arms
9.2.10Power Case Studies: OPEC
9.3IGOs, TNCs & Alliances
10Option 8A: Health & Human Rights (A2 only)
10.1Human Development
10.2Role of Governments & IGOs
10.3Human Rights
10.4Interventions
11Option 8B: Migration & Identity (A2 only)
11.1Globalisation & Migration
11.2Consequences of Migration
11.3Nation States
11.4Responses to Global Migration
Jump to other topics
1Tectonic Processes & Hazards
1.1Tectonic Processes & Hazards
1.2Natural Disasters
1.3Natural Disaster Case Studies
1.4Trends & Patterns
2Option 2A: Glaciated Landscapes & Change
2.1Glaciated Landscapes Over Time
2.2Periglacial Landscapes
2.3Glacial Processes
2.4Glacial Landforms
3Option 2B: Coastal Landscapes & Change
3.1Coastal Landscapes
3.2Coastal Erosion & Deposition
3.3Coastal Risks
4Globalisation
4.1Globalisation
4.2Negatives of Globalisation
4.3Global Shift
4.5Culture
4.6Measuring Development
5Option 4A: Regenerating Places
5.1Types of Economies
5.2Function of Places
5.3Regeneration
5.4Regeneration Case Studies
6Option 4B: Diverse Places
6.1Population Structure
6.2Past & Present Connections
6.3Urban & Rural Spaces
6.4Diversity
6.5Urban & Rural Case Studies
6.6Case Study - Tower Hamlets
6.7Case Study - Sturton-le-Steeple
7The Water Cycle & Water Insecurity (A2 only)
7.1Hydrological Processes Global to Local
7.2Influences on the Water Cycle
7.3Water Insecurity
8The Carbon Cycle & Energy Security (A2 only)
8.1The Carbon Cycle
8.2Energy Consumption
8.3Alternative Energy
8.4Growing Demand for Resources
9Superpowers (A2 only)
9.1Superpowers
9.2Hard & Soft Power
9.2.1Hard & Soft Power
9.2.2Emerging Powers - China Rivalry
9.2.3Emerging Powers - Chinese Sources of Power
9.2.4Emerging Powers - Brazil
9.2.5Emerging Powers - Russia
9.2.6Emerging Powers - India
9.2.7Theories of Development
9.2.8Power Case Studies: Chinese One Belt One Road
9.2.9Power Case Studies: Pakistan Nuclear Arms
9.2.10Power Case Studies: OPEC
9.3IGOs, TNCs & Alliances
10Option 8A: Health & Human Rights (A2 only)
10.1Human Development
10.2Role of Governments & IGOs
10.3Human Rights
10.4Interventions
11Option 8B: Migration & Identity (A2 only)
11.1Globalisation & Migration
11.2Consequences of Migration
11.3Nation States
11.4Responses to Global Migration
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