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Fault welding by pseudotachylyte formation

Mitchell, TM; Toy, V; Di Toro, G; Renner, J; Sibson, RH; (2016) Fault welding by pseudotachylyte formation. Geology , 44 (12) pp. 1059-1062. 10.1130/G38373.1. Green open access

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Abstract

During earthquakes, melt produced by frictional heating can accumulate on slip surfaces and dramatically weaken faults by melt lubrication. Once seismic slip slows and arrests, the melt cools and solidifies to form pseudotachylytes, the presence of which is commonly used by geologists to infer earthquake slip on exhumed ancient faults. Field evidence suggests that solidified melts may weld seismic faults, resulting in subsequent seismic ruptures propagating on neighboring pseudotachylyte-free faults or joints and thus leading to long-term fault slip delocalization for successive ruptures. We performed triaxial deformation experiments on natural pseudotachylyte-bearing rocks, and show that cooled frictional melt effectively welds fault surfaces together and gives faults cohesive strength comparable to that of an intact rock. Consistent with the field-based speculations, further shear is not favored on the same slip surface, but subsequent failure is accommodated on a new subparallel fault forming on an off-fault preexisting heterogeneity. A simple model of the temperature distribution in and around a pseudotachylyte following slip cessation indicates that frictional melts cool to below their solidus in tens of seconds, implying strength recovery over a similar time scale.

Type: Article
Title: Fault welding by pseudotachylyte formation
Open access status: An open access version is available from UCL Discovery
DOI: 10.1130/G38373.1
Publisher version: http://dx.doi.org/10.1130/G38373.1
Language: English
Additional information: ©The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1538627
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