Lithosphere Dynamics, Plate Tectonics, and Seismic Activity

Lithosphere Dynamics: Creation and Destruction

Oceanic vs. Continental Lithosphere

In the oceanic lithosphere, processes involving creation at divergent boundaries and destruction at convergent boundaries (subduction zones) generally balance each other. In contrast, the continental lithosphere is typically older because its creation rate is faster than its destruction rate, and growth primarily occurs at divergent boundaries.

Consequences of Plate Tectonics

Climate and Living Things

The movement of tectonic plates varies the arrangement of continents and oceans. This variation determines local climates and the distribution of different climatic zones across the planet, significantly impacting living organisms.

Geological Processes

The movement of plates causes changes on the Earth's surface, energizing or creating conditions for two main types of geological processes:

• Exogenous Geological Processes: These involve the action of the hydrosphere, atmosphere, and biosphere on surface rocks.
• Endogenous Geological Processes: These are produced by the Earth's internal heat and plate movement.

Tectonic Deformation and Stresses

Types of Stresses

• Compression: Forces pushing towards each other in opposite directions.
• Tension (Distension): Forces pulling apart.

Types of Deformation

• Elastic Deformation: When the stress is removed, the rock returns to its original shape. This is associated with earthquakes.
• Plastic Deformation: The rock is permanently deformed without fracturing. This results in folds.
• Rupture: When the stress exceeds the rock's strength, it fractures. This creates faults, joints, and can cause seismic activity.

Earthquakes: Causes and Waves

Earthquakes represent the sudden release of stored energy in rocks undergoing elastic deformation. From the hypocenter (the point of origin within the Earth), vibrations travel through the Earth's interior as seismic waves:

Earthquake Waves

• Primary (P) Waves: Vibrate parallel to the direction of wave travel. They are the fastest seismic waves.
• Secondary (S) Waves: Vibrate perpendicular (transverse) to the direction of wave travel. They are slower than P waves and cannot travel through liquids.
• Surface Waves: Travel along the Earth's surface, propagating outwards from the epicenter (the point on the surface directly above the hypocenter). They are the slowest but often the most destructive waves.

Geological Hazards and Seismic Risks

Risk Assessment Factors

Assessing endogenous risks involves considering:

• Value of the Affected Area: Measured by the potential loss of life and the economic value of properties and infrastructure.
• Vulnerability: The proportion of the value that is likely to be lost during an event.
• Danger (Hazard): The probability that a specific area will be affected by a hazardous event within a certain time frame.

Seismic Risk Impacts

Seismic risks can cause disasters rapidly. Potential impacts include:

• Damage to Constructions:
  • Heavy/Rigid Structures: Collapse, severe destruction.
  • Lightweight Structures: Falling eaves, chimneys, non-structural damage.
• Ground Effects: Differential settlement of soil, liquefaction, landslides.
• Coastal Effects: Tsunamis or seismic sea waves.
• Human Actions: Secondary effects like panic, looting, and disruption of services.