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Pseudotachylyte increases the post-slip strength of faults

B. Proctor and D. A. Lockner
Pseudotachylyte increases the post-slip strength of faults
Geology (Boulder) (December 2016) 44 (12): 1003-1006


Solidified frictional melts, or pseudotachylytes, are observed in exhumed faults from across the seismogenic zone. These unique fault rocks, and many experimental studies, suggest that frictional melting can be an important process during earthquakes. However, it remains unknown how melting affects the post-slip strength of the fault and why many exhumed faults do not contain pseudotachylyte. Analyses of triaxial stick-slip events on Westerly Granite (Rhode Island, USA) sawcuts at confining pressures from 50 to 400 MPa show evidence for frictional heating, including some events energetic enough to generate surface melt. Total and partial stress drops were observed with slip as high as 6.5 mm. We find that in dry samples following melt-producing stick slip, the shear failure strength increased as much as 50 MPa, while wet samples had <10 MPa strengthening. Microstructural analysis indicates that the strengthening is caused by welding of the slip surface during melt quenching, suggesting that natural pseudotachylytes may also strengthen faults after earthquakes. These results predict that natural pseudotachylyte will inhibit slip reactivation and possibly generate stress heterogeneities along faults. Wet samples do not exhibit melt welding, possibly because of thermal pressurization of water reducing frictional heating during slip.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 44
Serial Issue: 12
Title: Pseudotachylyte increases the post-slip strength of faults
Affiliation: U. S. Geological Survey, Earthquake Science Center, Menlo Park, CA, United States
Pages: 1003-1006
Published: 201612
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 26
Accession Number: 2017-005851
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2016337
Illustration Description: illus.
N41°10'00" - N42°01'60", W71°55'00" - W71°07'00"
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: 201705
Program Name: USGSOPNon-USGS publications with USGS authors
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