Tectonics: Faults

S. Stein*

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingChapter


Faults are surfaces in the Earth along which one side moves or has moved with respect to the other. They are identified either when an earthquake occurs or by geological mapping showing that motion across the fault has occurred in the past. Many faults are inactive, in the sense that there has been no motion across them within some defined time interval, typically the past million years or less. Other faults are active, in the sense that recent motion has occurred and hence motion might be expected in the future. Faults, and the earthquakes on them, are studied to understand both the regional tectonics and the mechanics of faulting. Typically, earthquakes occur on previously identified faults, demonstrate that the fault is active, and provide information on the fault’s geometry and the motion on it. For example, in the famous 1906 San Francisco earthquake, one of the first earthquakes to be carefully studied, several metres of relative motion occurred along several hundred kilometres of the San Andreas Fault. Hence, H Reid proposed the elastic-rebound theory of earthquakes, in which materials on opposite sides of the fault move relative to each other, but friction ‘locks’ the fault and prevents it from slipping (Figure 1). Eventually more strain accumulates than the fault rocks can withstand, and the fault slips in an earthquake. The motion is sometimes revealed after earthquakes by linear features, including roads and rows of trees (Figure 2). Those who study earthquakes seek to understand both the geological processes causing earthquakes....

Original languageEnglish (US)
Title of host publicationEncyclopedia of Geology
PublisherElsevier Inc
Number of pages9
ISBN (Print)9780123693969
StatePublished - Jan 1 2004

ASJC Scopus subject areas

  • General Engineering


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