Editing Earthquake (section)

===Fault types===
{{Further|Fault (geology)|Strike and dip}}
There are three main types of fault, all of which may cause an [[interplate earthquake]]: normal, reverse (thrust), and strike-slip. Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and where movement on them involves a vertical component. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip. The topmost, brittle part of the Earth's crust, and the cool slabs of the tectonic plates that are descending into the hot mantle, are the only parts of our planet that can store elastic energy and release it in fault ruptures. Rocks hotter than about {{cvt|300|C||}} flow in response to stress; they do not rupture in earthquakes.<ref>{{cite journal |last1=Sibson |first1=R.H. |year=1982 |title=Fault Zone Models, Heat Flow, and the Depth Distribution of Earthquakes in the Continental Crust of the United States |journal=Bulletin of the Seismological Society of America |volume=72 |issue=1 |pages=151–163}}</ref><ref>Sibson, R.H. (2002) "Geology of the crustal earthquake source" International handbook of earthquake and engineering seismology, Volume 1, Part 1, p. 455, eds. W H K Lee, H Kanamori, P C Jennings, and C. Kisslinger, Academic Press, {{ISBN|978-0-12-440652-0}}</ref> The maximum observed lengths of ruptures and mapped faults (which may break in a single rupture) are approximately {{cvt|1000|km|||}}. Examples are the earthquakes in [[1957 Andreanof Islands earthquake|Alaska (1957)]], [[1960 Valdivia earthquake|Chile (1960)]], and [[2004 Indian Ocean earthquake and tsunami|Sumatra (2004)]], all in subduction zones. The longest earthquake ruptures on strike-slip faults, like the [[San Andreas Fault]] ([[1857 Fort Tejon earthquake|1857]], [[1906 San Francisco earthquake|1906]]), the [[North Anatolian Fault]] in Turkey ([[1939 Erzincan earthquake|1939]]), and the [[Denali Fault]] in Alaska ([[2002 Denali earthquake|2002]]), are about half to one third as long as the lengths along subducting plate margins, and those along normal faults are even shorter.

==== Normal faults ====
Normal faults occur mainly in areas where the crust is being [[Extensional tectonics|extended]] such as a [[divergent boundary]]. Earthquakes associated with normal faults are generally less than magnitude 7. Maximum magnitudes along many normal faults are even more limited because many of them are located along spreading centers, as in Iceland, where the thickness of the brittle layer is only about {{convert|6|km|spell=in||}}.<ref>Hjaltadóttir S., 2010, "Use of relatively located microearthquakes to map fault patterns and estimate the thickness of the brittle crust in Southwest Iceland"</ref><ref>{{cite web |title=Reports and publications &#124; Seismicity &#124; Icelandic Meteorological office |url=http://en.vedur.is/earthquakes-and-volcanism/reports-and-publications/ |access-date=2011-07-24 |publisher=En.vedur.is |archive-date=2008-04-14 |archive-url=https://web.archive.org/web/20080414235419/http://en.vedur.is/earthquakes-and-volcanism/reports-and-publications/ |url-status=live }}</ref>

==== Reverse faults ====
Reverse faults occur in areas where the crust is being [[Thrust tectonics|shortened]] such as at a [[convergent boundary]]. Reverse faults, particularly those along convergent boundaries, are associated with the most powerful earthquakes (called [[megathrust earthquake]]s) including almost all of those of magnitude 8 or more. Megathrust earthquakes are responsible for about 90% of the total seismic moment released worldwide.<ref>{{citation |last1=Stern |first1=Robert J. |title=Subduction zones |journal=Reviews of Geophysics |volume=40 |issue=4 |page=17 |year=2002 |bibcode=2002RvGeo..40.1012S |doi=10.1029/2001RG000108 |s2cid=247695067|doi-access=free }}</ref>

==== Strike-slip faults ====
[[Strike-slip fault]]s are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Strike-slip faults, particularly continental [[Transform fault|transforms]], can produce major earthquakes up to about magnitude 8. Strike-slip faults tend to be oriented near vertically, resulting in an approximate width of {{cvt|10|km|||}} within the brittle crust.<ref>{{cite web |title=Instrumental California Earthquake Catalog |url=http://wgcep.org/data-inst_eq_cat |url-status=dead |archive-url=https://web.archive.org/web/20110725021215/http://wgcep.org/data-inst_eq_cat |archive-date=2011-07-25 |access-date=2011-07-24 |publisher=WGCEP}}</ref> Thus, earthquakes with magnitudes much larger than 8 are not possible.

[[File:Kluft-photo-Carrizo-Plain-Nov-2007-Img 0327.jpg|thumb|left|Aerial photo of the San Andreas Fault in the [[Carrizo Plain]], northwest of Los Angeles]]

In addition, there exists a hierarchy of stress levels in the three fault types. Thrust faults are generated by the highest, strike-slip by intermediate, and normal faults by the lowest stress levels.<ref>{{cite journal | last1 = Schorlemmer | first1 = D. | last2 = Wiemer | first2 = S. | last3 = Wyss | first3 = M. | year = 2005 | title = Variations in earthquake-size distribution across different stress regimes | journal = Nature | volume = 437 | issue = 7058| pages = 539–542 |bibcode = 2005Natur.437..539S |doi = 10.1038/nature04094 | pmid = 16177788 | s2cid = 4327471 }}</ref> This can easily be understood by considering the direction of the greatest principal stress, the direction of the force that "pushes" the rock mass during the faulting. In the case of normal faults, the rock mass is pushed down in a vertical direction, thus the pushing force (''greatest'' principal stress) equals the weight of the rock mass itself. In the case of thrusting, the rock mass "escapes" in the direction of the least principal stress, namely upward, lifting the rock mass, and thus, the overburden equals the ''least'' principal stress. Strike-slip faulting is intermediate between the other two types described above. This difference in stress regime in the three faulting environments can contribute to differences in stress drop during faulting, which contributes to differences in the radiated energy, regardless of fault dimensions.