Scaling seismic fault thickness from the laboratory to the field
- 1Institut des Sciences de la Terre d'Orléans, Université d'Orléans / CNRS UMR-7327, Orléans, France.
- 2Department of Earth Sciences, Durham University, Durham DH1 5ED, United Kingdom.
- 3Institut des Sciences de la Terre de Paris, Sorbonne Université, Campus Pierre et Marie Curie / CNRS UMR-7193, Paris, France.
- 4Laboratoire de Géologie de l'Ecole Normale Supérieure, PSL Research University / CNRS UMR-8538, Paris France.
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 six 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 depends 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.
How to cite: Ferrand, T. P., Nielsen, S., Labrousse, L., and Schubnel, A.: Scaling seismic fault thickness from the laboratory to the field, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12188, https://doi.org/10.5194/egusphere-egu21-12188, 2021.
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