Key Terms: Seismic Hazards (AQA A Level Geography): Revision Note

Nature and causes of seismic hazards - key terms

Collision plate margin – A tectonic boundary where two continental plates converge, producing powerful earthquakes without subduction.

Constructive plate margin – A boundary where tectonic plates move apart; earthquakes here are usually shallow and low in magnitude.

Destructive plate margin – A tectonic boundary where one plate subducts beneath another, causing intense and deep earthquakes.

Earthquake – The sudden, violent shaking of the Earth’s surface caused by the rapid release of energy from stress at plate boundaries or faults.

Epicentre – The point on the Earth’s surface directly above the earthquake’s focus.

Focus – The point within the Earth’s crust where an earthquake originates.

Intra-plate earthquake – An earthquake that occurs away from plate boundaries, often along ancient fault lines or hot spots.

Liquefaction – The process by which saturated soils temporarily lose strength during shaking, behaving like a liquid and causing buildings to sink or tilt.

L-wave (Love wave) – A surface wave that causes the most damage during an earthquake, moving the ground side-to-side.

P-wave (Primary wave) – A type of seismic wave that travels fastest, through both solids and liquids, causing back-and-forth motion.

S-wave (Secondary wave) – A slower seismic wave that moves only through solids and causes side-to-side and up-and-down movement.

Seismic waves – Vibrations that travel through the Earth during an earthquake, including P-waves, S-waves, and L-waves.

Slab pull – A tectonic process where a dense oceanic plate sinks into the mantle, pulling the rest of the plate with it.

Tectonic plate – A rigid segment of the Earth’s lithosphere that moves over the asthenosphere, causing seismic activity at boundaries.

Tsunami – A large sea wave caused by the sudden displacement of water due to undersea earthquakes, commonly occurring along subduction zones.

Prediction of seismic hazards - key terms

Deformation monitoring – The use of tools such as tiltmeters and strain meters to detect movement in the Earth's crust, which may indicate building stress.

Foreshocks – Smaller earthquakes that occur before a major event, sometimes acting as a warning sign of a larger quake.

Moment Magnitude Scale (MMS) – A logarithmic scale used to measure the energy released by an earthquake; more accurate than the older Richter scale.

Radon gas emissions – Changes in underground radon gas levels can precede seismic activity, though the correlation is not consistently reliable.

Seismic gap theory – The idea that a lack of recent earthquakes in a seismically active area may indicate a high risk of a future major quake.

Seismometer – An instrument that detects and records the vibrations caused by seismic waves.

Strain meter – A device used to measure small deformations in the ground, indicating stress accumulation.

Tiltmeter – A sensitive instrument that measures changes in slope or ground tilt, often caused by rising magma or tectonic movement.

Impacts of seismic hazards - key terms

Cultural loss – The destruction of historic or religious sites (e.g. temples, towers) that affects cultural identity and heritage.

Economic impact – The financial consequences of an earthquake, including repair costs, loss of trade, unemployment, and GDP decline.

Environmental impact – Earthquakes can cause landslides, forest loss, contamination of rivers, and destruction of ecosystems.

Homelessness – A secondary effect where people are displaced from their homes due to building damage or destruction.

Injury and death – Primary effects of seismic activity, often resulting from collapsing buildings, infrastructure failure, or tsunamis.

Political instability – Earthquakes can expose weaknesses in government response, leading to social unrest, protest, or policy change.

Primary impact – Immediate effects such as collapsed buildings, infrastructure failure, and casualties.

Secondary impact – Longer-term consequences including homelessness, disease, economic loss, and disruption to services.

Social impact – Effects on people’s lives, including disruption of education, healthcare, and access to basic services.

Management of seismic hazards - key terms

Adaptation – Changing human behaviour and practices to minimise earthquake risk, such as storing emergency kits or modifying infrastructure.

Building codes – Regulations ensuring structures are built to withstand seismic activity, including reinforced steel and cross-bracing.

Disaster preparedness – Efforts to educate and train populations, conduct drills, and raise awareness about earthquake safety.

Early warning system – Technology that detects seismic waves and sends alerts seconds before shaking reaches the surface.

Emergency aid – Immediate relief provided after a disaster, including food, water, shelter, medical supplies, and rescue efforts.

GIS crisis mapping – A tool used to coordinate response and recovery by mapping damage and identifying priority areas for aid.

Land-use zoning – Planning tool that restricts construction in high-risk areas, such as liquefaction zones or steep slopes.

Mitigation – Actions taken to reduce the severity of an earthquake’s impact, e.g. tsunami walls or quake-proof buildings.

Prevention – While earthquakes can’t be prevented, actions such as land-use planning can prevent increased exposure to risk.

Preparedness – Ensuring that emergency plans, supplies, and education are in place prior to an event.

Search and rescue – Operations to find and assist people trapped by collapsed buildings or debris.

Tsunami wall – Coastal barriers built to reduce the impact of tsunami waves on settlements.