Postseismic

Postseismic refers to the interval after a major earthquake during which the crust continues to deform and the seismic system evolves toward a new equilibrium. It follows the coseismic rupture and may last from weeks to years.

The dominant processes are afterslip on the fault plane and nearby faults, viscoelastic relaxation in the lower crust and upper mantle, and poroelastic rebound due to redistribution of fluids. Each process has different time scales and geographic signatures, and they can operate simultaneously.

Postseismic deformation is measured with GPS, InSAR, borehole strainmeters, and seismic networks. Observed surface displacements and aftershock sequences inform models of fault rheology and crustal structure. Temporal decay of deformation rates often follows a power-law or exponential trend.

Understanding postseismic behavior improves hazard assessment for aftershocks and ground shaking, informs estimates of total slip deficit, and helps constrain the rheological properties of the crust and upper mantle.