SCEC Award Number 21135 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Evaluating magnitudes of potential off-fault viscous deformation through laboratory creep experiments on fractured granite rocks
Investigator(s)
Name Organization
Hiroki Sone University of Wisconsin, Madison
Other Participants
SCEC Priorities 3e, 2a, 3d SCEC Groups Geodesy, Geology, FARM
Report Due Date 03/15/2022 Date Report Submitted 03/14/2024
Project Abstract
 Through laboratory rock mechanics experiments, we investigate the magnitude of any potential time-dependent (or viscous) mechanical behavior of damaged crustal rocks at relatively shallow depth conditions. By deforming damaged granite samples at hydrothermal conditions, we evaluate to what extent off-fault crustal rocks could deform via inelastic mechanisms. We prepared a set of Westerly granite samples heated at high temperatures (600 degC) to produce synthetic damage zone rocks. Heat treatment led to reduction in ultrasonic velocities confirming presence of microfractures. Samples tested in a triaxial apparatus exhibit substantial creep behavior. However, whether temperature and presence of water enhances the occurrence of creep deformation remained unclear despite our expectation that hydrothermal conditions would accelerate creep. Results however show that substantial amount of creep deformation can take place in fault damage zone which may need to be acknowledged in fault zone models.
Intellectual Merit While the laboratory program supported in this project will not fully constrain the constitutive formulation required to capture the full extent of inelastic rheological behavior of rocks at crustal conditions, we provide quantitative data that demonstrate the occurrence of plastic creep deformation in micro-fractured rocks analogous to fault damage zone rocks. Our results contribute in SCEC research objectives such as P3e, P2a, and P3d.
Broader Impacts Constraining the extent of off-fault permanent deformation is crucial for properly assessing seismic hazards in Southern California as it has direct implication on how quickly earthquake driving forces build up in the earth. The project will also provide opportunities for a graduate research assistant.
Exemplary Figure Figure 3, Axial strain measured by the LVDTs during the experiment. Strains in unit of microstrain.