Clay mineral reactions at earthquake timescales

Julia Krogh, Heather M. Savage, Randolph Williams, & Christie D. Rowe

Published September 11, 2022, SCEC Contribution #12547, 2022 SCEC Annual Meeting Poster #113

Both long-term and transient fault strength are affected by the production and localization of frictionally weak phases, such as clays. Clay mineral alteration occurs in faults from fluid-rock interactions at geothermal temperatures over time. However, the effects of earthquake-like conditions on clay mineral phases have not been thoroughly explored. A greater understanding of how clays change during earthquakes from friction-induced heating, as well as how they recover in the time afterwards, would provide new insight into the co- and post- seismic strength of faults. Previous work investigating the temperatures at which clay mineral reactions produce fossil earthquake signatures has examined rapid in situ structural and chemical changes below 250 °C. Reactions above this temperature have only been studied under long heating times that are unrealistic for earthquake conditions.

Here we present the results of smectite heating experiments. Our samples are a homogenized montmorillonite standard from the Clay Mineral Society, processed to a sub-2-micron grain size and spiked with nano-corundum prior to analysis. A heating stage mounted in a Rigaku Smartlab Powder Diffractometer has enabled us to collect in situ X-ray diffraction (XRD) data at temperatures up to 900 °C. Scans in the immediate aftermath of 100 °C/min temperature ramps and at discrete post-ramp time intervals of 20 and 30 minutes qualitatively show dehydration, dehydroxilation, and decomposition reactions. We show preliminary estimates of clay kinetics and extrapolate our results to earthquake timescales.

Citation
Krogh, J., Savage, H. M., Williams, R., & Rowe, C. D. (2022, 09). Clay mineral reactions at earthquake timescales. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology