Coulomb stress transfer
Coulomb stress transfer is a seismic-related geological process of stress changes to surrounding material caused by local discrete deformation events. Using mapped displacements of the Earth’s surface during earthquakes, computed Coulomb stress changes have suggested that stress relieved during an earthquake does not only dissipate, but can also move up and down fault segments, concentrating and promoting subsequent tremors. Importantly, Coulomb stress changes have been applied to earthquake-forecasting models that have been used to assess potential hazards related to earthquake activity.
The Coulomb failure criterion requires that the Coulomb stress exceeds a value σf defined by the shear stress τB, normal stress σB, pore pressure p, and coefficient of friction μ of a failure plane, such that
It is also often assumed that changes in pore fluid pressure induced by in changes stress are proportional to the normal stress change across the fault plane. These effects are incorporated into an effective coefficient of friction μ’, such that
This simplification allows for the calculation of Coulomb stress changes on a fault plane to be independent of the regional stress field but instead depends on the fault geometry, sense of slip, and coefficient of friction.
The significance of the Coulomb stress changes was discovered when mapped displacements of neighbouring fault movements were used to calculate Coulomb stress changes along faults. Results revealed that the stress relieved on faults during earthquakes did not simply dissipate, but also moved up and down fault segments. Moreover, mapped lobes of increased and decreased Coulomb stress around local faults exhibited increased and decreased rates of seismicity respectively shortly after neighboring earthquakes, but eventually return to their background rate over time.
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