Quartz fluid inclusion abundance and off-fault damage in a deeply exhumed, strike-slip, seismogenic fault
Publication Name: Journal of Structural Geology
Publication URL: https://doi.org/10.1016/j.jsg.2020.104118
Off-fault damage zones comprise highly fractured rocks surrounding the dynamic slip surface of faults. These damage zones modify fault-zone rheology and rupture dynamics by changing the bulk elastic properties and modulating fluid flow. Damage zones in the brittle upper crust, reaching widths >100 m, are commonly characterized by measuring fracture density, but identifying the extent of off-fault damage in deeply exhumed faults is challenging due to post- and inter-seismic viscous/plastic deformation. We measured fluid inclusion abundance in quartz deformed at ~400–500 °C from an ancient seismogenic strike-slip fault/shear zone to evaluate whether it can be a proxy for damage-zone width. In contrast to upper crustal fault zones displaying a high-low trend of healed microfracture density, the shear zone has a low-high-low trend of fluid inclusion abundance from the core toward the host rock. We find that pattern explicable through removal of fluid inclusions by recrystallization after co-seismic deformation, allowing us to use fluid inclusion abundance to measure damage zone extent, which is >~80 m (the low-high abundance region) from the shear zone core. Our findings indicate that extensive co-seismic damage zones may extend from Earth’s surface to the base of the seismogenic zone, well within the frictional-to-viscous transition.
This research was supported by National Science Foundation grants EAR-1727090 and EAR-0820946.
Song, W. J., Johnson, S. E., & Gerbi, C. C. (2020). Quartz fluid inclusion abundance and off-fault damage in a deeply exhumed, strike-slip, seismogenic fault. Journal of Structural Geology, 139, 104118. https://doi.org/10.1016/j.jsg.2020.104118