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Gouge graphitization and dynamic fault weakening during the 2008 Mw 7.9 Wenchuan earthquake

Li-Wei Kuo, Li Haibing, Steven A. F. Smith, Giulio Di Toro, John Suppe, Sheng-Rong Song, Stefan Nielsen, Hwo-Shuenn Sheu and Si Jialiang
Gouge graphitization and dynamic fault weakening during the 2008 Mw 7.9 Wenchuan earthquake
Geology (Boulder) (January 2014) 42 (1): 47-50

Abstract

The 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.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 42
Serial Issue: 1
Title: Gouge graphitization and dynamic fault weakening during the 2008 Mw 7.9 Wenchuan earthquake
Affiliation: National Taiwan University, Taipei, Taiwan
Pages: 47-50
Published: 201401
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 19
Accession Number: 2014-004537
Categories: Structural geologySeismology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2014012
Illustration Description: illus. incl. geol. sketch map
Secondary Affiliation: Chinese Academy of Geological Sciences, Institute of Geologu, CHN, ChinaInstituto Nazionale di Geofisica e Vulcanologia, ITA, ItalyNational Synchrotron Radiation Research Center, TWN, Taiwan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201404
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