seismiccycle

The seismic cycle, or earthquake cycle, is the quasi-periodic sequence of processes that rebuild and release elastic strain in faults as a result of plate tectonics. It is typically described as comprising three overlapping phases: interseismic, coseismic, and postseismic. During the interseismic phase, most fault segments are locked or partially locked and tectonic forces cause the surrounding rocks to accumulate elastic strain. The duration of this phase depends on plate motion rates, the locking depth of the fault, and material properties. The coseismic phase involves a rapid rupture and abrupt release of stored energy, producing ground shaking and seismic waves. The fault undergoes a sudden change in slip, transferring stress to adjacent fault segments and sometimes triggering additional earthquakes. The postseismic phase includes processes that relax the newly established stress state, such as afterslip on the fault, viscoelastic or poroelastic relaxation in the crust and upper mantle, and transient deformation that gradually approaches a new equilibrium.

Observations of the seismic cycle rely on geodetic measurements (GPS, InSAR) and seismic catalogs to track fault locking, deformation, and rupture history. The cycle is often modeled with elastic rebound theory and rate-and-state friction laws, which describe how frictional resistance evolves with slip and slip rate. While the cycle explains many regularities in fault behavior, real faults can show irregular recurrence, multi-segment ruptures, partial ruptures, and complex postseismic transients, limiting deterministic prediction. Probabilistic forecasts remain the common tool for hazard assessment, focusing on changes in earthquake likelihood rather than precise timing.