RII Track-4: NSF: Gouge Mineral Strain Mapping under Shearing and Implications for EGS-Induced Seismicity

University Of Alaska Fairbanks Campus, Fairbanks AK

Investigators

Abstract

The frequency of induced earthquakes has increased dramatically over the past few years globally due to massive fluid injection in enhanced geothermal systems (EGS), where small perturbations may prematurely trigger earthquakes. Recent observations associated with EGS and a purposely reactivated fault in a field pilot experiment exhibit significantly larger magnitudes than predicted. The increased likelihood of inducing large seismic events has jeopardized several geothermal projects. However, there is not a clear understanding of these events and the prevention and mitigation of EGS-induced seismic events are still a concern. With the transmission of Alaska EGS from shallow hot springs to deep borehole drilling, there is a pressing need to develop a better understanding of the mechanism of triggering the seismicity with the influence of heat exchange and fluids intrusion. This fellowship project will experimentally investigate the property evolution of the fault gouge with thermal treatment to reveal the triggering mechanism of ESG-related seismicity from a microscale perspective. The project will build on the capacity of geohazards evaluation and EGS-related geo-risk evaluation in Alaska through extended collaborations with institutions in the lower forty-eight (48) states. These research resources acquired through the fellowship project will be leveraged to develop new course and workshop materials to provide women, minorities, and Alaska remote community students with research experience and training. This Research Infrastructure Improvement Track-4 EPSCoR Research Fellows (RII Track-4:NSF) project would provide a fellowship to an Assistant Professor and training for a graduate student at the University of Alaska Fairbanks (UAF). The PI proposes to develop a novel fault sliding test system in collaboration with experts from the Center for Geomechanics, Geofluids, and Geohazards at the Pennsylvania State University. It has been proved that the mineral lattice strain in the gouge layer is critical for predicting the residual stress on the surface and its failure status. Mineral strain variation with thermal treatment and fluid intrusion within the fault gouge layer is critical for predicting localized stability that initializes seismic events. However, direct evidence has not been reported in the lab to identify and quantify the mineral strains due to the hurdle and difficulties of direct measurement of mineral strains under in situ conditions with a dynamic sliding process. The proposed test system enables the unique capacity of using neutron diffraction to conduct mineral strain mapping of the gouge layer with shear sliding. The stick-slip faulting test will be conducted using the proposed test system with thermal treatment and fluid intrusion. Combining neutron diffraction and nanoindentation techniques, the properties of minerals in the gouge layer will be investigated from a microscale perspective to reveal the triggering mechanism of ESG-related seismicity. The proposed test system enables the investigation of the evolution of mineral properties under shearing and its implications on seismic events with thermal treatment and fluids intrusion. The outcome will provide a unique perspective for evaluating the EGS-related geohazards and their prediction and prevention. 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.