SCEC Award Number 22084 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Experimental Investigation of Multi-scale Flash Weakening - Continuation Project
Investigator(s)
Name Organization
Frederick Chester Texas A&M University Judith Chester Texas A&M University
Other Participants Ph.D. student: Ms. Santa Guerrero Bonnett
SCEC Priorities 1d, 3c, 2d SCEC Groups FARM, SDOT, Geology
Report Due Date 03/15/2023 Date Report Submitted 03/15/2024
Project Abstract
We investigated frictional heating during high-speed sliding in rock to better constrain theoretical-based models of flash weakening. The conventional model of flash heating at micrometer-scale contacts can explain dramatic reduction of friction during earthquake slip. The model also treats the progressive rise in macroscopic surface temperature with displacement that further reduces friction. We have conducted high-acceleration, high-speed friction experiments that mimic earthquake rupture and slip using a biaxial apparatus equipped with an IR camera to record flash temperature distributions on the sliding surfaces. Sliding surfaces are machined to create two dominant length scales (µm and mm) of roughness that are consistent with natural faults. Our unique data set allows us to document the inhomogeneous surface temperature distribution that is characterized by mm-size hot-spots comprising approximately 10-15% of the macroscopic surface area. Based on thermal modeling of the observed flash temperature distributions, we determine the local normal stress magnitude at the mm-scale hot spots, which allows us to test the conventional flash weakening model assuming micrometer contacts. We find that the conventional model does not capture well the observed transient weakening and strengthening behavior in experiments. Hypothesizing that flash-weakening friction may involve independent mechanisms at the mm and micrometer length scales, we developed a multi-scale flash-weakening model. While the multi-scale flash-weakening model better resolves the transient and hysteretic friction observed in experiments, there remain some systematic discrepancies. We suggest flash weakening models may be advanced by considering additional processes of fracture, wear, plowing and localization/delocalization processes at multiple length scales.
Intellectual Merit The suite of rock deformation experiments conducted with our unique machine that can achieve high acceleration and deceleration, sliding between blocks of rock up to 1 m/s slip, and high speed IR imaging to document temperature distribution on sliding surfaces, allow us to test conventional theoretical models of dynamic weakening by flash heating. Employing carefully machined sliding surfaces, and using microscopy and profilometry before and after sliding, are designed to identify the underlying, multiphysics processes responsible for the observed macroscopic response. Such information is key to developing accurate mathematical descriptions of evolving fault strength and the effects of frictional heating and shear localization. The outcomes of this research are useful to inform physics-based earthquake models including numerical models of nucleation, propagation and arrest of earthquakes. This project has developed novel experimental techniques and unique data sets that can be used to test, constrain and refine theoretical models of friction, instability, and rupture propagation in fault zones.
Broader Impacts This project has supported training and learning of graduate student researchers, particularly within the SCEC group of researchers in our College. The project has broadened the participation of underrepresented groups, specifically by supporting research of two Ph.D. graduate students, both women, one of which is Hispanic-Latina. Both students have been and will continue to be involved in SCEC.
Exemplary Figure Figure 4
Comparisons between modeled friction (dashed lines) and measured friction (solid lines) with sliding velocity (b) and displacement (c) for Experiment 436. Multi-scale model results for the non-global, best fitting parameter set (brown dashed line) are plotted alongside single- scale model results (pink dotted-dashed line).
Figure from Barbery et al., 2023