tectonics theory

Plate Boundaries

  • convergent (destructive subduction) - oceanic crust is meeting continental, since oceanic is more dense, when they meet, it dives down. it goes down into the magma chambers, and pressure builds. It releases as a volcano

  • convergent (continental collision) - two continental plates move together, the land between the two plates buckles and rises up, forming fold mountains

  • divergent - the plates move apart from one another. When this happens the magma from the mantle rises up to make (or construct) new crust. The movement of the plates over the mantle can cause earthquakes. Rising magma can also create shield volcanoes.

  • conservative - when two plates slide against eachother the same way along a fault/weakness. friction occurs and they become stuck. pressure builds and it is then released suddenly in an earthquake

Types of volcanoes

  • composite - triangular and round, steep sides and a crater on top. anacidic lava is high in silica making it thick. it flows slowly and travels short distances before cooling. violent eruptions with long periods of time in-between them. found on convergent boundaries where oceanic plates subduct

  • sheild - gentle sides. basaltic lava, which is high in temperature and low in silica with low gas content, fluid lava with very little explosive activity. destroys property but rarely kills, less violent eruptions, lava flows for a long time before it solidifies

  • hotspots - different plumes and round in a semi-triangular shape. viscous, granitic lava that erupts explosively. plumes are fixed in place.

Primary volcanic hazards

  • lava flows - Basalt fissure eruptions are the most dangerous reaching speeds of over 50km per hour on steep slopes and can spread tens of kilometres from their source. Andesitic and rhyolitic lavas move slowly and rarely spread more than 8km from their source.

  • pyroclastic flow - A mixture of hot rock fragments, lava particles and ash buoyed up by hot gases. Can move at high speeds up to 300 km per hour and can extend up to 40km from their source. Temperatures within the flow are commonly 100-700°C.

  • ash and tephra fall - Communities near volcanoes are at the greatest risk for ashfall although it can be a problem hundreds of miles from a volcano after a major eruption. Volcanic ash can create eye and upper airway irritation. Ashfall can cause minor to major damage to vehicles and buildings, contaminate water supplies, disrupt sewage and electrical systems, and damage or kill vegetation.

  • volcanic gases - Various gases can be emitted by active volcanoes before, during or after an eruptive event and can cause various health hazards locally, but also have the potential to affect the climate globally. Volcanic gases are particularly hazardous as they cannot be seen and, because they are denser than ambient air, can ‘pond’ in depressions around an active volcano.

Secondary volcanic hazards

  • lahars - Volcanic ash mixes with water to form a dense slurry like freshly mixed concrete. The slurry known as a lahar can flow downslope at over 50 km per hour.

  • volcanic landslides - These are gravity-driven slides of masses of rock and loose volcanic material. Often occur during an eruption, as with Mount St. Helens when the North side of the volcano collapsed. Landslides can occur at other times on volcanic craters because of heavy rainfall or earthquakes.

  • tsunamis - Generated by explosive eruptions on volcanic islands or by submarine caldera collapse. Waves generated may reach tens of metres up to 100 metres in height.

Earthquakes

  • Earthquakes are vibrations caused by earth movements at plate boundaries and at major fault lines (cracks in the earth’s surface).

  • They can occur at all plate boundaries but the most severe earthquakes are normally found at conservative and destructive subduction plate boundaries

  • tectonic plates are always moving. If they get stuck, a huge pressure can build up. When the plates break free or one plate gives way, the energy released causes an earthquake beneath Earth’s surface at the focus. Seismic waves spread out from the focus through the rock and reach the surface at the epicentre.

  • The focus is the point at which the rock moves. Seismic waves start at the focus.

  • The epicentre is directly above the focus on the earth’s surface and will be the area which experiences the worst effects.

Deep focus earthquake:

70-700km below the earth’s surface. These occur at destructive plate boundaries and can be very powerful, but the seismic waves spread out vertically so a fairly small area suffers the damage.

Shallow focus earthquake:

<70km. These occur at conservative boundaries and in the upper part of destructive and collision boundaries. Since the seismic waves spread out horizontally, they can cause damage over a large area.

Primary Impact - things that happen as a direct result of the earthquake

Secondary impact - things that happen as a result of the primary impacts

The Moment Magnitude scale

The amount of energy released in an earthquake is called the magnitude, which is measured using the Moment Magnitude scale.

The MM scale** **is a logarithmic scale, which means every number is ten times more powerful than the previous level. So 7.0 is ten times more powerful that 6.0 and 100 times more powerful than 5.0.

Earthquake Preparedness

1. Practice Drills

Practice drills train people to respond quickly and calmly during an earthquake.

  • Drills teach actions such as “Drop, Cover, Hold On”

  • Regular drills in schools, workplaces, and public buildings reduce panic

  • Improve reaction time and help people remember safe behaviour

  • Identify weaknesses in evacuation plans

Limitations:
Drills may not reflect the confusion of a real earthquake; people may not take them seriously; they do not prevent damage to buildings.

2. Emergency Kits and Supplies

Emergency kits provide essential items needed immediately after an earthquake.

  • Typically include water, non-perishable food, first aid kits, torches, radios, batteries, and blankets

  • Help people survive when services such as electricity, water, and transport are disrupted

  • Reduce pressure on emergency services

Limitations:
Many people do not prepare kits; supplies may be insufficient for large families or long disruptions; kits can be expensive for low-income households.

3. Public Education and Training

Education helps people understand earthquake risks and how to stay safe.

  • Public campaigns teach safe actions before, during, and after earthquakes

  • Training explains how to secure furniture and identify safe places indoors

  • Reduces injuries and loss of life by encouraging correct responses

  • Builds a culture of preparedness in earthquake-prone areas

Limitations:
Education relies on continued funding and access to information; knowledge may fade over time; not all groups (e.g. tourists or vulnerable populations) may be reached.

Earthquake Protection

1.        Earthquake-resistant building design
These methods help buildings absorb shaking without collapsing.

  • Base isolation
    Buildings sit on rubber or steel bearings that absorb earthquake movement, so less shaking reaches the structure.

  • Shock absorbers / dampers
    Similar to car shock absorbers; they reduce movement by absorbing energy.

  • Cross-bracing
    Steel or concrete braces (often in an X shape) strengthen walls and stop them from swaying too much.

  • Shear walls
    Thick reinforced walls that resist sideways movement.

  • Flexible materials
    Steel and wood bend slightly instead of cracking like rigid materials.

  • Deep foundations
    Piles are driven into stable ground to prevent buildings from sinking or tipping.

  • Lightweight roofs
    Reduce the risk of collapse and injury if failure occurs.

Limitations: Very expensive; older buildings may not be protected; extremely strong earthquakes can still cause damage. Can be expensive.

2.        Land-use planning
Reduces the risk by avoiding dangerous locations. Eg. Avoids building on fault lines or unstable ground; uses open spaces for safety.

Limitations: Not always possible in densely populated or already-developed cities.

3. Retrofitting old buildings
Improving buildings built before modern safety standards. For example, adding steel braces or shear walls, strengthening foundations and securing heavy objects inside buildings.

Limitations: Costly and time-consuming; some buildings cannot be fully upgraded.

Earthquake prediction

1.     Historical Seismic Records
Scientists study past earthquakes to identify patterns and estimate where future quakes are likely. This helps planners and engineers prepare, but it cannot predict the exact timing of an earthquake.

Strengths: Identifies high-risk areas; useful for long-term planning

Limitations: Cannot predict exact time; earthquakes are irregular

Example: San Andreas Fault, California

2. GPS & Plate Motion Monitoring
GPS sensors measure how tectonic plates slowly move and accumulate stress along faults. These measurements show where stress is building but cannot tell when it will be released.

Strengths: Detects stress buildup precisely; identifies high-risk faults

Limitations: Stress does not indicate exact rupture timing

Example: Japan’s GPS network along the Pacific Plate

3. Foreshocks
Small earthquakes sometimes occur before a larger event. However, most small quakes do not lead to big ones, so foreshocks are unreliable as a warning.

Strengths: May indicate an imminent quake

Limitations: Most small quakes are not foreshocks; cannot be confirmed until after the main quake

Example: 2011 Tōhoku earthquake, Japan

4. Ground Deformation
Satellites and ground instruments measure subtle changes in the Earth’s surface caused by stress buildup. These can identify stressed areas but cannot predict when an earthquake will occur.

Strengths: Detects subtle crustal changes; maps stressed faults

Limitations: Deformation doesn’t always trigger earthquakes

Example: Fault monitoring in California and Turkey

5. Early Warning Systems
Sensors detect seismic waves after an earthquake starts and send alerts before strong shaking reaches people. This can save lives but only gives seconds to tens of seconds of warning.

Strengths: Provides very short warning; reduces damage and injuries

Limitations: Quake already started; limited warning time

Example: ShakeAlert (USA), Japan Earthquake Early Warning

6. Experimental / Unreliable Methods
Some scientists study unusual animal behaviour, gas emissions, or electromagnetic signals as potential quake indicators. Results are inconsistent, so these methods are not scientifically reliable.

Strengths: Stimulates research and ideas

Limitations: Unproven; inconsistent results

Example: Claims of animals predicting earthquakes have failed rigorous testing