What is a Fault Zone - inferences from stress state

Greg Hirth

Submitted August 15, 2019, SCEC Contribution #9747, 2019 SCEC Annual Meeting Talk on Mon 1330 (PDF)

Poster Image: 
When I was invited to help convene a panel discussion on the question “What is a fault zone?” my immediate reaction was to think of a Scholz/Sibson style synoptic model of a strike slip fault that extends from to surface to beneath the brittle-ductile transition. Through my own work on topics related to the brittle-ductile transition, I am convinced that rocks from many deforming regions support stresses in the range of 100 MPa (based on observations of microstructures in rocks exhumed from the brittle-ductile transition, extrapolation of lab data, measurements of stresses in boreholes, and larger scale geodynamic constraints). At this same time, I acknowledge the wide range of observations that don’t mesh well with a the decades-old view of a fault zone rheology based on “Byerlee friction” in the seismogenic zone and a transition to dislocation creep at higher temperature (e.g., heat flow anomalies, triggered LFEs at the base of the crust, subduction zone seismicity, the lack of a clear depth dependence to estimated earthquake stress drops). As part of the discussion, we will urge us all to consider how understanding fault zone structures at different scales and tectonic environments (from the surface through the lithosphere), and the mechanical processes that form them, can be used to constrain these problems and potentially resolve apparent discrepancies.

Hirth, G. (2019, 08). What is a Fault Zone - inferences from stress state. Oral Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)