Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/9311
AuthorsKuo, L.* 
Li, H.* 
Smith, S. A. F.* 
Di Toro, G.* 
Suppe, J.* 
Song, S* 
Nielsen, S. B.* 
Sheu, H.* 
Si, J.* 
TitleGouge graphitization and dynamic fault weakening during the 2008 Mw 7.9 Wenchuan earthquake
Issue DateNov-2013
Series/Report no.1/42(2013)
DOI10.1130/G34862.1
URIhttp://hdl.handle.net/2122/9311
KeywordsWenchuan
drilling project
Earthquakes
Rock mechanics
Subject Classification04. Solid Earth::04.01. Earth Interior::04.01.04. Mineral physics and properties of rocks 
04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones 
04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution 
04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics 
AbstractThe Longmenshan fault that ruptured during the 2008 Mw 7.9 Wenchuan (China) earthquake was drilled to a depth of 1200 m, and fault rocks including those in the 2008 earthquake slip zone were recovered at a depth of 575–595 m. We report laboratory strength measurements and microstructural observations from samples of slip zone fault rocks at deformation conditions expected for coseismic slip at borehole depths. Results indicate that the Longmenshan fault at this locality is extremely weak at seismic slip rates. In situ synchrotron X-ray diffraction analysis indicates that graphite was formed along localized slip zones in the experimental products, similar to the occurrence of graphite in the natural principal slip zone of the 2008 Wenchuan rupture. We surmise that graphitization occurred due to frictional heating of carbonaceous minerals. Because graphitization was associated with strong dynamic weakening in the experiments, we further infer that the Longmenshan fault was extremely weak at borehole depths during the 2008 Wenchuan earthquake, and that enrichment of graphite along localized slip zones could be used as an indicator of transient frictional heating during seismic slip in the upper crust.
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