# Active fault
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> Source: https://en.wikipedia.org/wiki/Active_fault
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{{Short description|Geological fault likely to be the source of an earthquake sometime in the future}}
[[File:San_Andreas_Fault_Aerial_View.gif|thumb|[San Andreas Fault](/source/San_Andreas_Fault) ]]
An '''active fault''' is a [fault](/source/fault_(geology)) that is likely to become the source of another [earthquake](/source/earthquake) 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.[
{{cite web
| title =Active fault
| work =Earthquake Glossary
| publisher =USGS Earthquake Hazards Program
| date =November 3, 2009
| url =https://earthquake.usgs.gov/learn/glossary/?term=active%20fault
| format =online web page
| access-date =2011-09-17}}
*{{USGS}}]
Active faulting is considered to be a [geologic hazard](/source/geologic_hazard) – one related to [earthquakes](/source/earthquakes) as a cause. Effects of movement on an active fault include [strong ground motion](/source/strong_ground_motion), surface faulting, [tectonic deformation](/source/Tectonics), [landslide](/source/landslide)s and [rockfall](/source/rockfall)s, [liquefaction](/source/liquefaction), [tsunami](/source/tsunami)s, and [seiche](/source/seiche)s.[
Quaternary faults are those active faults that have been recognized at the surface and which have evidence of movement during the [Quaternary](/source/Quaternary) Period.][
Related [geological](/source/geology) disciplines for ''active-fault'' studies include [geomorphology](/source/geomorphology), [seismology](/source/seismology), [reflection seismology](/source/reflection_seismology), [plate tectonics](/source/plate_tectonics), [geodetics](/source/geodetics) and [remote sensing](/source/remote_sensing), [risk analysis](/source/Quantitative_risk_analysis), and others.][
== Location ==
Active faults tend to occur in the vicinity of [tectonic plate](/source/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 [remote sensing](/source/remote_sensing) 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.][{{Cite book
| last =Slemmons
| first =D. Burton
| last2 =and Defolo
| first2 =Craig
| title =Active Tectonics: Impact on Society
| publisher =The [National Academies Press](/source/National_Academies_Press)
| year =1986
| chapter =Evaluation of Active Faulting and Associated Hazards
| chapter-url =https://books.google.com/books?id=qaz9KnE2lxQC&pg=PA45
| pages =45–48
| isbn =978-0-309-07395-0
}}
*Organizations that authored this book: Geophysics Study Committee, Geophysics Research Forum, National Research Council]
== Geologic conditions in U.S. ==
The geologic conditions and [tectonic setting](/source/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](/source/1811%E2%80%9312_New_Madrid_earthquakes), a large earthquake near [Charleston, South Carolina](/source/1886_Charleston_earthquake) in 1886, and the [Cape Ann earthquake](/source/Cape_Ann_earthquake) northeast of Boston in 1755.[
{{cite web
|title=... relationship between Quaternary faults and earthquakes
|work=Quaternary Faults
|publisher=USGS Earthquake Hazards Program
|date=October 27, 2009
|url=https://earthquake.usgs.gov/learn/faq/?faqID=267
|format=online web page
|access-date=2011-09-17
|url-status=dead
|archive-url=https://web.archive.org/web/20111127121851/http://earthquake.usgs.gov/learn/faq/?faqID=267
|archive-date=November 27, 2011
}}
*{{USGS}}][
{{cite web
|title=... so many earthquakes and Quaternary faults in the Western U.S.
|work=Quaternary Faults
|publisher=USGS Earthquake Hazards Program
|date=October 27, 2009
|url=https://earthquake.usgs.gov/learn/faq/?faqID=269
|format=online web page
|access-date=2011-09-17
|url-status=dead
|archive-url=https://web.archive.org/web/20111127122904/http://earthquake.usgs.gov/learn/faq/?faqID=269
|archive-date=November 27, 2011
}}
*{{USGS}}]
== References ==
{{Reflist}}
== External links ==
* [https://web.archive.org/web/20100525104129/http://maps.gns.cri.nz/website/af/ Active faults of New Zealand]: an interactive map of active faults near a plate boundary
* [http://www.conservation.ca.gov/cgs/rghm/ap The Alquist-Priolo Earthquake Fault Zoning (AP) Act]
* [https://pubs.usgs.gov/fs/2004/3033/fs-2004-3033.html Quaternary Fault and Fold Database for the Nation]
{{Authority control}}
Category:Active faults
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Adapted from the Wikipedia article [Active fault](https://en.wikipedia.org/wiki/Active_fault) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Active_fault?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.