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'Fossil Earthquakes' Abundant

Date:
January 29, 2009
Source:
Seismological Society of America
Summary:
Rocks formed only under the extreme heat and friction during earthquakes, called pseudotachylytes, may be more abundant than previously reported, according to new research focused on eight faults found in the Sierra Nevada.

Rocks formed only under the extreme heat and friction during earthquakes, called pseudotachylytes, may be more abundant than previously reported, according to new research focused on eight faults found in the Sierra Nevada. 

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Geologists have previously debated whether these rocks are rarely produced or not based on an apparent absence in the rock record, most likely brought about by the difficulty in identifying them. Only a small fraction of the energy released in an earthquake is consumed by seismic waves, the formation of pseudotachylytes reveals the importance of the heat generated by the earthquake process.

Pseudotachylytes form by frictional melting during co-seismic faulting at significant depths in the crust. They are not easy to identify, requiring evidence that the fault rock has passed through a melt phase. They are generated by frictional heating of the slip surface, the melting of which may account for a significant proportion of energy released during an earthquake.

Past surveys of the Sierra Nevada, which reported an absence of pseudotachylytes, have focused on the geometry and mechanics of the faults rather than the geological details of the rock types and composition. However, the authors of this study report an abundance of pseudotachylytes throughout the area. The pseudotachylytes they describe range from easily identified to impossible to identify from field data alone. The authors suggest further study of pseudotachylytes will ultimately reveal more about energy partitioning during earthquakes.


Story Source:

The above story is based on materials provided by Seismological Society of America. Note: Materials may be edited for content and length.


Journal Reference:

  1. Kirkpatrick et al. Pseudotachylytes: Rarely Generated, Rarely Preserved, or Rarely Reported? Bulletin of the Seismological Society of America, 2009; 99 (1): 382 DOI: 10.1785/0120080114

Cite This Page:

Seismological Society of America. "'Fossil Earthquakes' Abundant." ScienceDaily. ScienceDaily, 29 January 2009. <www.sciencedaily.com/releases/2009/01/090128160816.htm>.
Seismological Society of America. (2009, January 29). 'Fossil Earthquakes' Abundant. ScienceDaily. Retrieved November 27, 2014 from www.sciencedaily.com/releases/2009/01/090128160816.htm
Seismological Society of America. "'Fossil Earthquakes' Abundant." ScienceDaily. www.sciencedaily.com/releases/2009/01/090128160816.htm (accessed November 27, 2014).

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