1. V. Fault Mechanisms and Earthquake Generation
Stress and Strain
Elastic and Plastic Strain
Stick-slip and Elastic Rebound
Fault Failure Propagation

2. V. Fault Mechanisms and Earthquake Generation
Stress and Strain
Stress represents a force applied to a material
Strain represents the response of the material to stress
Change of shape
Change of position
Elastic and Plastic Strain
Stick-slip and Elastic Rebound
Fault Failure Propagation

3. V. Fault Mechanisms and Earthquake Generation
Stress and Strain
Elastic and Plastic Strain
Elastic strain = change of shape but returns to original position when stress is remove (e.g. rubber band)
Elastic strain represents stored energy
When the stress is removed, the stored strain energy is released
Plastic strain = change of shape that does not return to original position when stress is remove (e.g. modeling clay)
Stick-slip and Elastic Rebound
Fault Failure Propagation

4. V. Fault Mechanisms and Earthquake Generation
Stress and Strain
Elastic and Plastic Strain
Stick-slip and Elastic Rebound
Fault surface sticks (no slip) while plate motion continues to apply stress
Rocks respond with both elastic and plastic strain
Fault “fails” (slips) elastic strain rebounds and generates seismic waves
Releases stored elastic strain energy
We have an earthquake!
In general the greater built-up strain = larger magnitude earthquake
Fault Failure Propagation

5. V. Fault Mechanisms and Earthquake Generation
Elastic Rebound

6. V. Fault Mechanisms and Earthquake Generation
Stress and Strain
Elastic and Plastic Strain
Stick-slip and Elastic Rebound
Fault Failure Propagation
Modification of the elastic rebound model
Slip propagates along a fault surface, releasing some but not all of the elastic energy

7. V. Fault Mechanisms and Earthquake Generation
Fault Propagation

8. V. Fault Mechanisms and Earthquake Generation
Northridge, CA (1994) – 6.7 M
Example of fault plane propagation,
8 seconds of rupture up the fault plane