Surface rupture#Normal faulting

File:Running track after 1999 Chichi earthquake in Taiwan.jpg during the 1999 Jiji earthquake, Taiwan]]

Not every earthquake results in surface rupture, particularly for smaller and deeper earthquakes. In some cases, however, the lack of surface effects is because the fault that moved does not reach the surface. For example, the 1994 Northridge earthquake had a moment magnitude of 6.7, caused major damage in the Los Angeles area, occurred at {{convert|18.2|km|mi|0|abbr=on}} below the Earth's surface, but did not cause surface rupture, because it was a blind thrust earthquake.{{cite web|url=http://pasadena.wr.usgs.gov/info/nr10/|title=USGS Northridge Earthquake 10th Anniversary|access-date=13 April 2016}}

Surface ruptures commonly occur on pre-existing faults. Only rarely are earthquakes (and surface ruptures) associated with faulting on entirely new fault structures.{{Cite web|url=https://www.earthquakeauthority.com/Prepare-Your-House-Earthquake-Risk/Geologic-Hazards/Surface-Rupture|title=Ground Rupture & Surface Faulting – Earthquake Ground Displacement | CEA|access-date=Jan 1, 2020}} There is shallow hypocenter, and large fracture energy on the asperities,{{cite web | url=https://pubs.geoscienceworld.org/ssa/bssa/article-abstract/98/3/1147/341883/surface-rupturing-and-buried-dynamic-rupture | title=Surface Rupturing and Buried Dynamic-Rupture Models Calibrated with Statistical Observations of Past Earthquakes | publisher=pubs.geoscienceworld.org | access-date=28 October 2018 | author=Dalguer, Luis A.; Miyake, Hiroe; Day, Steven M.; Irikura, Kojiro}} the asperity shallower than {{convert|5|km|mi}}. Examples of such earthquakes are San Fernando earthquake, Tabas earthquake, and Chi-Chi earthquake.{{cite web | url=http://www.iitk.ac.in/nicee/wcee/article/WCEE2012_1629.pdf | title=Generation Mechanism of Surface and Buried Faults Considering the Effect of Plasticity in a Shallow Crust Structure | publisher=iitk.ac.in | access-date=31 October 2018 | author=Wada, K.; Goto, H.}}

In surface rupture earthquakes, the large slips of land are concentrated in the shallow parts of the fault.{{cite web | url=https://www.terrapub.co.jp/journals/EPS/pdf/2004/5601/56010003.pdf | title=Differences in ground motion and fault rupture process between the surface and buried rupture earthquakes | publisher=Earth Planets Space | date=14 March 2004 | access-date=26 October 2018}} And, notably, permanent ground displacements which are measureable can be produced by shallow earthquakes, of magnitude M5 and greater.{{Cite web |url=https://earthquake.usgs.gov/research/eqproc/grdmotion.php |title=Earthquake Processes and Effects |publisher=United States Geological Survey}}

The form that surface rupturing takes depends on two things: the nature of the material at the surface and the type of fault movement.

File:Earthquake- road crack.jpg, Jiji, Nantou County, Taiwan]]

Where there are thick superficial deposits overlying the trace of the faults, the resulting surface effects are typically more discontinuous. Where there is little or no superficial deposits, the surface rupture is generally continuous, except where the earthquake rupture affects more than one fault, which can lead to complex patterns of surface faulting, such as in the 1992 Landers earthquake.{{Cite journal |last1=Zachariesen J. |last2=Sieh K. |year=1995 |title=The transfer of slip between two en echelon strike-slip faults: A case study from the 1992 Landers earthquake, southern California |url=https://earthobservatory.sg/files/publications/pdf/The%20transfer%20of%20slip%20between%20two%20en%20echelon%20strike-slip%20faults.pdf |journal=Journal of Geophysical Research |volume=100 |issue=B8 |pages=15,281–15,301 |doi=10.1029/95JB00918|bibcode=1995JGR...10015281Z |hdl=10220/8475 }}

Surface ruptures associated with normal faults are typically simple fault scarps. Where there are significant superficial deposits, sections with more oblique faulting may form sets of en-echelon scarp segments. Antithetic faults may also develop, giving rise to surface grabens.

Reverse faulting (particularly thrust faulting) is associated with more complex surface rupture patterns since the protruding unsupported part of the hanging-wall of the fault is liable to collapse. In addition there may be surface folding and back-thrust development.

File:Denali Fault surface rupture.png

Strike-slip faults are associated with dominantly horizontal movement, leading to relatively simple linear zones of surface rupture where the fault is a simple planar structure. However, many strike-slip faults are formed of overlapping segments, leading to complex zones of normal or reverse faulting depending on the nature of the overlap. Additionally, where there are thick superficial deposits, the rupture typically appears as a set of en-echelon faults.{{Cite journal |last1=Tchalenko J.S. |last2=Ambraseys N.N. |year=1970 |title=Structural Analysis of the Dasht-e Bayaz (Iran) Earthquake Fractures |journal=GSA Bulletin |volume=81 |issue=1 |pages=41–60 |doi=10.1130/0016-7606(1970)81[41:SAOTDB]2.0.CO;2}}

To retrofit a house to survive surface rupture requires engineered design by geotechnical, and structural or civil engineers. This can be quite expensive.

• Aseismic creep
• Ground fissure
• Vertical displacement

{{Reflist}}

• [http://www.earthquakegeology.com/materials/projects/1620R-report.pdf A large article about surface rupture]

Category:Earthquake and seismic risk mitigation

Category:Seismology

Category:Geological hazards