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

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

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

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

V. Fault Mechanisms and Earthquake Generation Elastic Rebound

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

V. Fault Mechanisms and Earthquake Generation Fault Propagation

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