Earthquake Surface Rupture, Fissures, and Tectonic Uplift/Subsidence

Primary reference(s)

PNSN, no date. Surface rupture. Pacific Northwest Seismic Network (PNSN). Accessed 24 November 2019.

Styron, R., 2019. Coseismic uplift and subsidence: An underappreciated seismic threat. Global Earthquake Model Foundation (GEM) Hazard Blog. Accessed 24 November 2019.

USGS, no date. Surface faulting. United States Geological Survey (USGS). 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. Surface ruptures, fissures, and uplift and subsidence are all manifestations of this longer-term deformation, and although less dramatic, may all pose hazards during and after earthquakes (Styron, 2019).

Metrics and numeric limits

The size and spatial extent of surface ruptures, fissures and uplift/subsidence depend on the type, magnitude and depth of the earthquake as well as the distance from the earthquake.

Surface ruptures are expected in about half of continental Magnitude 6 earthquakes, with an expectation that increases to 100% for continental earthquakes at Magnitude 8 and greater (Biasi and Weldon, 2006). Displacements vary from a few centimetres for earthquakes at the low end of this range and near the edges of larger earthquakes, up to 15–20 m for the largest possible continental earthquakes, around Magnitude 8 (Biasi and Weldon, 2006). Fissures are generally much smaller and more spatially distributed than surface ruptures.

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).

Both of 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.

Examples of drivers, outcomes and risk management

Earthquake surface ruptures, fissures, and tectonic uplift/subsidence are caused by earthquakes of sufficient magnitude and proximity to the Earth’s surface to cause permanent ground deformation. Surface ruptures and fissures are generally limited to the area near the causative fault’s intersection with the Earth’s surface, while uplift and subsidence can occur over a much broader region (Styron, 2019).

Surface ruptures and fissures can cause damage to buildings, roads, and utility infrastructure (e.g., gas and water lines). In addition to the immediate, local risk posed by collapsing infrastructure, this damage may hamper rescue and rebuilding efforts by impeding transportation and utility delivery. In the worst cases, damage to lifelines may cause local flooding (e.g., water lines), environmental impacts (e.g., oil pipelines) and even highly destructive fires (gas lines) that may be more damaging than the initial earthquake. There is also potential for disruption due to flooding or re-routing of rivers if the river channel is sufficiently modified (Holbrook and Schumm, 1999).

While no technology exists for reducing these or other earthquake hazards, the risk to infrastructure posed by surface rupture and fissures can be partly mitigated by not building on known fault traces, seismic retrofitting of existing buildings, and engineering of pipelines with enough flexibility to absorb the displacement by bending and flexing, rather than breaking (e.g., USGS, 2003).

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.