International FEP List - Version 3
FEP 1.2.4 Seismicity

The release of energy accumulated in rocks via rapid relative movements within the Earth’s crust and/or mantle, usually along faults or geological interfaces. Seismic events are most common in tectonically active or volcanically active regions at or near crustal plate margins. Human-induced or triggered seismic events (i.e. caused by human activities such as fluid injection) may occur both in naturally seismically active areas and in areas characterised by low background seismicity.

Seismicity has the potential to physically disturb the waste, EBS, the surrounding rocks and the ground surface. Observations have shown that the effects of a seismic event are greater at the surface than underground.

Seismicity could affect the pressure gradients in fluids (aqueous- and non-aqueous liquids and gases) in and around the repository, thereby leading to movements of these fluids. Seismic pumping of fluids along faults, characterised by cyclical pressure increases and decreases during repeated seismic events, is an example of this kind of phenomenon. Releases of energy during seismic events are characterised by the propagation of vibrations (seismic waves). These waves may disturb the geosphere and engineered structures, both at the ground surface and underground, although the intensity of these waves and the consequent likelihood of significant disturbances decreases at progressively greater depths. If the seismic event originates within or close to a repository (i.e. a fault moves within or in close proximity to a repository) then a pathway could be created for migration of fluids from the repository. The underground pressure pulse from such an event could also drive the movement of such fluids. The potential effects of seismic events on the repository include liquefaction of the seal or backfill materials, shaking and damage to waste packages, rockfalls, modification of the properties of the Excavation Damaged Zone (EDZ) around the repository and shafts, and extension or creation of fractures near the repository and shafts. The geosphere might be affected by the growth of existing faults or the creation of new faults. Seismicity may affect the nature of surface and near-surface environments, including the biosphere, in the vicinity of a repository. Thus, seismicity may influence the nature of receptors that might be impacted by any radionuclides or other contaminants that might be transported from a repository in the post-closure periods. Tsunamis, land-slips, liquefaction of soil and collapse of surface structures are examples of changes in the surface and near-surface environment that might be caused by seismicity.