Collaborative Research: The rheological behavior of gouge at high temperature

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Major earthquakes are generated along faults in Earth’s tectonic plates as rocks are sheared past each other. Assessing the hazard associated with a fault zone requires understanding the conditions that promote earthquake nucleation. Shearing on faults can occur in an unstable manner, where rapid slip allows an earthquake to nucleate, or in a stable manner, where slip is steady and suppresses earthquake nucleation. Although much work has been devoted to understanding the conditions that lead to earthquake nucleation in the relatively cold portions of Earth’s crust, there is still a considerable gap in knowledge regarding the stability of faults in hotter regions. These hotter regions include the conduits of explosive volcanoes and transform faults in the oceans. Our work will determine the influence of temperature on fault stability to enable accurate assessments of hazard and risk in these regions. This work will also provide training to early-career researchers at the postdoctoral, graduate, and undergraduate levels. The team involved in this research will also work to introduce high-temperature experimental rock physics to groups typically underrepresented in the sciences via international conferences, and they will run a short-course on earthquakes and faulting to be offered to early-career researchers around the world in an in-person and virtual format.We will specifically answer three questions related to fault stability at high temperatures. First, how do extreme temperatures affect the strength and stability of fault materials? To answer this question, we will conduct deformation experiments on fault materials over a wide range of conditions. Second, what microscopic mechanisms control the strength of fault materials, and how do they compete with one another? To answer this question, we will use high-resolution microscopy to compare mechanical measurements with theoretical models based on the microphysics of rock deformation. Third, how do these mechanisms interact to determine fault stability, and what does this mean for the depth range of earthquakes in natural settings? To answer this question, we will assess the relationships among microscopic features, the macroscopic strength, the observed stability, and the rate of deformation. The net result of these observations will be a refined model for the stability of fault zones at high temperatures, which we will then compare to available catalogs of earthquake locations in relatively “hot” regions to test our predictions of the depth range of earthquake nucleation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.