Fluid-Induced Magnetic Enhancement in Sandstone Friction Experiments: Implications for Coseismic Fault Temperature Estimates

Abstract

Constraining peak temperature during seismic slip is essential for quantifying earthquake energy budgets and fault weakening. Rock magnetic methods provide a sensitive means of estimating shear-induced coseismic temperature rise; however, the role of fluids in friction-induced magnetic alterations remains poorly constrained. Here we present the first experimental investigation into fluid effects, performing rotary-shear experiments (peak slip rate of 5 cm/s) under dry and fluid-saturated conditions on simulated fault gouges prepared from Slochteren Sandstone (Groningen gas field, The Netherlands), followed by comprehensive rock magnetic analysis. Dry shearing produced negligible magnetic changes, whereas fluid-saturated shearing generated pronounced magnetic enhancement, grain growth of magnetic minerals, and the formation of metallic iron in the simulated fault gouge. Our results demonstrate that fluid-mediated magnetic alterations occur in the absence of strong frictional heating. These findings highlight the need to assess the role of fluids in modifying the magnetic signatures of fault rocks.