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What is a fault zone? A perspective from beneath the brittle-ductile transition

Elena A. Miranda

Published August 21, 2019, SCEC Contribution #9919, 2019 SCEC Annual Meeting Talk on Mon 1330 (PDF)

Poster Image: 
The term “fault zone” evokes an image of a localized, brittle feature that we associate with seismicity or creep in tectonically active regions. However, when we broaden our perspective to characterize the fault zones that comprise plate boundaries, we must also consider the shear zones that extend down-dip from brittle faults, beneath the brittle-ductile transition. The vicinity of the brittle-ductile transition is an important region where down-dip propagation of rupture can induce brittle deformation in rocks otherwise deforming by crystal plastic deformation. Conversely, the high stresses (~100-150 MPa) inferred from ductile rocks at the base of the brittle-ductile transition may also promote the critical loading of weak faults above the brittle-ductile transition. The degree to which temporal and spatial variations in brittle and ductile deformation can promote vertical linkage between fault zones and shear zones is therefore important for characterizing lithospheric-scale discontinuities like plate boundaries. In this panel discussion, I offer a summary of key features of shear zones both in the vicinity of the brittle-ductile transition and in the lower crust, and I emphasize the use of field observations and microstructural analysis of naturally deformed rocks in investigating shear zones. I also highlight a number of research questions that motivate future interdisciplinary work: 1) what are the unique structures in the rock record that are produced by the full range of fault slip behavior, 2) how do we quantify the rheology of rocks that undergo non-steady-state co-seismic deformation at the BDT, and 3) are the structures resulting from steady-state and transient deformation distinct from each other, and how can we discern them in naturally deformed rocks?

Miranda, E. A. (2019, 08). What is a fault zone? A perspective from beneath the brittle-ductile transition. Oral Presentation at 2019 SCEC Annual Meeting.

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