Remotely triggered earthquakes

{{Short description|Geographical phenomenon}}

{{Earthquakes}}

Remotely triggered earthquakes are a result of the effects of large earthquakes at considerable distance, outside of the immediate aftershock zone."The locations of observed remotely triggered earthquakes suggest that intraplate crust is not critically stressed everywhere, but rather in certain regions where long-lived stress concentrations persist." [http://pasadena.wr.usgs.gov/office/hough/page.trigger.html Remotely Triggered Earthquakes: Observations, Interpretations] The farther one gets from the initiating earthquake in both space and time, the more difficult it is to establish an association.

The physics of triggering an earthquake are complex. Most earthquake-generating zones are in a state of being close to failure. If such a zone were to be left completely alone, it would generate significant earthquakes spontaneously. Remote earthquakes, however, are in a position to disturb this critical state, either by shifting the stresses statically, or by dynamic change caused by passing seismic waves.

The first type of triggering may be due to static changes in the critical state. For example, after the magnitude 7.3 Landers earthquake struck California in 1992, it is said that "the earthquake map of California lit up like a Christmas tree"."When the magnitude 7.3 Landers earthquake struck in 1992 in the desert north of Palm Springs, the earthquake map of the state of California lit up like a Christmas tree." [http://www.iris.edu/hq/files/programs/education_and_outreach/distinguished_lectureship/docs/IRIS_lecturers_2005.pdf The Very Long Reach of Very Large Earthquakes] This event reinforced the idea of remotely triggered earthquakes, and pushed the hypothesis into the scientific mainstream. Following the 2004 Indian Ocean earthquake, it was established that remote earthquakes had been triggered as far away as Alaska.{{cite journal|last1=West|first1=Michael|last2=Sanches|first2=John J.|last3=McNutt|first3=Stephen R.|url=http://www.sciencemag.org/cgi/content/abstract/308/5725/1144|title=Periodically Triggered Seismicity at Mount Wrangell, Alaska, After the Sumatra Earthquake|journal=Science|date=20 May 2005|volume=308|issue=5725|pages=1144–1146|doi=10.1126/science.1112462|pmid=15905395|bibcode=2005Sci...308.1144W|s2cid=27869948}}

There is scientific evidence for a "long reach", mainly in the form of discrete element modelling used in the mining industry. If rock is modeled as discrete elements in a critical state, a single disturbance can influence a wide area. A smaller-scale example is when a small excavation in a valley triggers a landslide and brings down a whole mountainside.