Fig. 4
(A) Schematic model showing the evolution of the Hebgen Lake Fault through pre-seismic (1), interseismic (2) and co-seismic deformation steps. (B) AMS fabric model for the Hebgen Lake Fault showing a symmetrical structural zonation for the hematite-rich fault mirror (A3). The oblate symmetry of the AMS in this material (Supplementary Figure S6) also supports precipitation in a planar conduit. Since goethite developed slickenlines in mirror A2 and these mirrors grade into hematite-rich mirrors (A3), and most likely shear deformation of goethite affected slab 2 as well. The AMS K1 direction (magnetic lineation) in slab 3 is interpreted to represent quasi-exclusively the direction of fluid flow, per descensum, along the dip direction of the HLF plane. In contrast, in slab 2, the pre-existing downdip fluid flow direction recorded by AMS is modified by shear deformation, resulting in a shallower plunging K1 direction and shallower dipping magnetic foliation (plane to K3 axis). (C) Summary of thermo-chemical constraints of frictional heating (0–700 °C). The left side of the middle arrow (pure Gth to Hem) represents temperatures from experiments on pure goethite (see text for details) whereas the right side of this arrow represents the HLF rock thermomagnetic experiments (Fig. 3G,H).
