Scaling Seismic Fault Thickness From the Laboratory to the Field

Ferrand, Thomas P.; Nielsen, Stefan; Labrousse, Loïc; Schubnel, Alexandre

Abstract

Pseudotachylytes originate from the solidification of frictional melt, which transiently forms and lubricates the fault plane during an earthquake. Here, we observe how the pseudotachylyte thickness a scales with the relative displacement D both at the laboratory and field scales, for measured slip varying from microns to meters, over 6 orders of magnitude. Considering all the data jointly, a bend appears in the scaling relationship when slip and thickness reach ∼1 mm and 100 µm, respectively, i.e., MW > 1. This bend can be attributed to the melt thickness reaching a steady-state value due to melting dynamics under shear heating, as is suggested by the solution of a Stefan problem with a migrating boundary. Each increment of fault is heating up due to fast shearing near the rupture tip and starting cooling by thermal diffusion upon rupture. The building and sustainability of a connected melt layer depend on this energy balance. For plurimillimetric thicknesses (a > 1 mm), melt thickness growth reflects in first approximation the rate of shear heating which appears to decay in D−1/2 to D−1, likely due to melt lubrication controlled by melt + solid suspension viscosity and mobility. The pseudotachylyte thickness scales with moment M0 and magnitude MW; therefore, thickness alone may be used to estimate magnitude on fossil faults in the field in the absence of displacement markers within a reasonable error margin.

Citation

Ferrand, T. P., Nielsen, S., Labrousse, L., & Schubnel, A. (2021). Scaling Seismic Fault Thickness From the Laboratory to the Field. Journal of Geophysical Research. Solid Earth, 126(3), Article e2020JB020694. https://doi.org/10.1029/2020jb020694

• Journal Article Type: Article
• Acceptance Date: Dec 22, 2020
• Online Publication Date: Mar 26, 2021
• Publication Date: 2021-03
• Deposit Date: Apr 7, 2021
• Publicly Available Date: Nov 25, 2021
• Journal: Journal of Geophysical Research: Solid Earth
• Print ISSN: 2169-9313
• Electronic ISSN: 2169-9356
• Publisher: American Geophysical Union
• Peer Reviewed: Peer Reviewed
• Volume: 126
• Issue: 3
• Article Number: e2020JB020694
• DOI: https://doi.org/10.1029/2020jb020694
• Public URL: https://durham-repository.worktribe.com/output/1244760
• Related Public URLs: https://onlinelibrary.wiley.com/share/author/MQTAAAG3VYD9SR9BYRMN?target=10.1029/2020JB020694