An active fault is a fault that is likely to become the source of another

earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,000 years. * Active faulting is considered to be a geologic hazard – one related to earthquakes as a cause. Effects of movement on an active fault include strong ground motion, surface faulting, tectonic deformation,

landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...

s and rockfalls, liquefaction,

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

s, and seiches. Quaternary faults are those active faults that have been recognized at the surface and which have evidence of movement during the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

Period. Related

geological Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth s ...

disciplines for ''active-fault'' studies include

geomorphology Geomorphology () is the scientific study of the origin and evolution of topographic and bathymetric features generated by physical, chemical or biological processes operating at or near Earth's surface. Geomorphologists seek to understand wh ...

seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...

, reflection seismology, plate tectonics, geodetics and

remote sensing Remote sensing is the acquisition of information about an physical object, object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring inform ...

risk analysis In simple terms, risk is the possibility of something bad happening. Risk involves uncertainty about the effects/implications of an activity with respect to something that humans value (such as health, well-being, wealth, property or the environ ...

, and others.

Location

Active faults tend to occur in the vicinity of tectonic plate boundaries, and active fault research has focused on these regions. Active faults tend to occur less within the area of any given plate. The fact that intraplate regions may also present seismic hazards has only recently been recognized.

Measurement

Various geologic methods are used to define the boundaries of an active fault such as

and magnetic measurements, as well as other ways. Several types of data, such as seismologic reports or records over time, are used to gauge fault activity. Activity and fault area are correlated, and risk analysis is employed with other factors to determine the potential earthquake hazard. *Organizations that authored this book: Geophysics Study Committee, Geophysics Research Forum, National Research Council

Geologic conditions in U.S.

The geologic conditions and plate tectonic setting in much of the Western U.S. has resulted in the region being underlain by relatively thin crust and having high heat flow, both of which can favor relatively high deformation rates and active faulting. In contrast, in the Central and Eastern U.S. (CEUS) the crust is thicker, colder, older, and more stable. Furthermore, the CEUS is thousands of miles from active plate boundaries, so the rates of deformation are low in this region. Nevertheless, the CEUS has had some rather large earthquakes in historical times, including a series of major earthquakes near New Madrid, Missouri in 1811–1812, a large earthquake near

Charleston, South Carolina Charleston is the List of municipalities in South Carolina, most populous city in the U.S. state of South Carolina. The city lies just south of the geographical midpoint of South Carolina's coastline on Charleston Harbor, an inlet of the Atla ...

in 1886, and the Cape Ann earthquake northeast of Boston in 1755. * *

References

External links

Active faults of New Zealand
an interactive map of active faults near a plate boundary
The Alquist-Priolo Earthquake Fault Zoning (AP) Act

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