Overview
This lecture reviews the elastic rebound theory, its relationship to stress and strain in rocks, and how these processes lead to earthquakes.
Stress and Strain Review
- Stress is force per unit area on rocks, including compression (squeezing), tension (stretching), and shear (sliding).
- Strain is the deformation resulting from stress on rocks.
- Types of strain include elastic strain (temporary deformation), ductile deformation (permanent bending), and brittle deformation (breakage).
Elastic Rebound Theory
- Elastic rebound theory was developed after the 1906 San Francisco earthquake.
- Rocks along a fault deform and store elastic strain energy as they bend under stress.
- When stress exceeds the rock’s strength, rupture occurs and an earthquake is generated.
- The stored elastic strain energy is rapidly released during the earthquake.
- After the rupture, unbroken rocks return to their original shape, but their positions are displaced.
- This process is most common at plate boundaries but can occur elsewhere.
Elastic Rebound Illustration
- Over tens to hundreds of years, rocks bend and accumulate elastic energy from tectonic movement.
- When the stress exceeds frictional resistance at the fault, sudden movement occurs, releasing energy as an earthquake.
- After the earthquake, rocks return to their shape but are offset, similar to a broken stick snapping back.
Key Terms & Definitions
- Stress — force applied per unit area on a material.
- Strain — deformation resulting from applied stress.
- Elastic Strain — temporary deformation that is recovered once the stress is released.
- Elastic Rebound Theory — the theory that earthquakes occur when energy stored in deformed rocks is suddenly released during fault slip.
Action Items / Next Steps
- Watch the recommended one-minute demonstration video on elastic rebound in Canvas.
- Prepare for the next lecture on seismic waves produced by fault ruptures.