Earthquake nucleation

Earthquake nucleation is the process by which slip on a small fault region grows into a self-sustaining rupture. It links slow fault loading to rapid seismic shaking.

Rate-and-state friction: A friction law describing how fault strength changes with sliding speed and contact history. Its frictional parameters determine whether accelerating slip can become unstable.
Fault (geology): A fracture or zone of fractures in rock across which displacement has occurred. Nucleation takes place on a fault surface or within its slipping zone.
Laboratory earthquake: A rapid slip event generated on a small fault surface in a controlled experiment. Laboratory events let researchers measure nucleation processes directly.
Stick-slip motion: Alternating periods of sticking and abrupt sliding between surfaces under shear stress. It provides a simple experimental analogue of repeated fault loading and rupture.
Critical nucleation length: The minimum slipping-patch size above which frictional instability can grow rather than decay. It defines the scale a nucleating patch must exceed to launch rupture.
Elastic rebound theory: The theory that earthquakes release elastic strain accumulated as rocks deform around locked faults. It explains the gradual loading that brings a fault patch toward instability.
Acoustic emission: High-frequency elastic waves emitted by small, sudden changes in a material. Its signals can reveal microfracturing and slip before a laboratory rupture.
Laboratory fault: A frictional interface between rock samples used to study fault behavior under controlled conditions. Researchers observe how nucleating slip evolves across an instrumented fault surface.
Frictional instability: A loss of stable sliding in which frictional weakening allows slip to accelerate. Nucleation is the localized development of this instability on a fault.
Static friction: Resistance to the initiation of sliding between surfaces that are not moving relative to each other. Fault contacts can resist slip until local stress overcomes their strength.

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