Subsidence and Uplift, Including Shoreline Change (Earthquake Trigger)
Primary reference(s)
Styron, R., 2019. Coseismic uplift and subsidence: An underappreciated seismic threat. Global Earthquake Model Foundation (GEM) Hazard Blog. Accessed 24 November 2019.
Additional scientific description
Most earthquakes are caused by displacement (sliding) of the Earth’s crust at a fault. The relative motion of the crust on either side of the fault results in persistent or permanent deformation of the Earth’s surface, in addition to the ground shaking resulting from the sudden release of energy during the earthquake. Tectonic uplift and subsidence are manifestations of this longer-term deformation, and though less dramatic, they may all pose hazards during and after earthquakes (Styron, 2019).
Metrics and numeric limits
The size and spatial extent of tectonic uplift or subsidence depends on the type, magnitude and depth of the earthquake as well as the distance from the earthquake.
Tectonic uplift and subsidence are generally as large or larger than the displacement of the surface rupture; moderate to large earthquakes in the crust that do not rupture to the surface will still broadly warp the region. The magnitude of the displacement will decrease with increasing distance from the earthquake, but in the case of ruptures on inclined faults such as subduction zones (rather than vertical strike-slip faults) uplift or subsidence of at least 1 m may extend more than 200 km from the fault trace for the largest earthquakes (Styron, 2019).
These effects will extend along the length of the earthquake fault, a distance of a few kilometres for Magnitude 6 earthquakes to more than 1000 km for Magnitude 9 earthquakes.
Key relevant UN convention / multilateral treaty
Not identified.
Examples of drivers, outcomes and risk management
Tectonic uplift and subsidence are caused by earthquakes of sufficient magnitude and proximity to the Earth’s surface to cause permanent ground deformation. Tectonic uplift and subsidence can occur over a broad region around the causative fault (GEM, 2019).
Tectonic uplift and subsidence are not generally destructive, with the exception of earthquakes on coastal faults. These events, particularly large subduction zone earthquakes, can cause persistent (decades-long) or permanent reconfigurations of a coastline. Uplift during an earthquake can lead to dramatic decreases in the depth and utility of harbours. Subsidence during a Magnitude 8–9 subduction zone earthquake can cause coastal communities, highways, and other infrastructure to sink below sea level, and the establishment of a new shoreline inland by several tens to hundreds of metres (Plafker, 1965).
References
GEM, 2019. For a world that is resilient to earthquakes. Global Earthquake Model Foundation (GEM). Accessed 14 October 2020.
Plafker, G., 1965. Tectonic deformation associated with the 1964 Alaska earthquake. Science, 148:1675-1687.
Styron, R., 2019. Coseismic uplift and subsidence: An underappreciated seismic threat. Global Earthquake Model Foundation (GEM) Hazard Blog. Accessed 24 November 2019.