SCEC Award Number 22151 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Correlation between creep and acoustic emission during earthquake preparation
Name Organization
Roman Makhnenko University of Illinois at Urbana-Champaign
Other Participants Nikita Bondarenko
SCEC Priorities 2d, 3a, 3f SCEC Groups FARM, SDOT
Report Due Date 03/15/2023 Date Report Submitted 03/16/2023
Project Abstract
Experiments on brittle creep behavior are conducted in order to investigate the laboratory-scale analog for earthquake nucleation process. Creep tests are performed with Berea sandstone at various initial stress states, fluid saturation, and drainage conditions. High correlation between low-temperature high-stress creep deformation rate and acoustic emission activity is observed in all conducted tests. Significant variations of b-value in magnitude-frequency relation during macroscopic failure preparation are observed independently of experimental conditions, making this parameter potentially suitable as a prognostic feature of earthquake preparation process. Presence of non-aqueous fluid is found to have little effect on the creep deformation and acoustic emission. On the other hand, presence of aqueous fluid exhibits the first-order effect both in case of water and CO2-water mixture. Additionally, dilatant hardening is observed during undrained creep test, while a significant increase of effective mean stress acting on the material can provide the stabilizing factor during the earthquake nucleation. This phenomenon is expected to be relevant for tight rock with low permeability that might behave in quasi-undrained manner
Intellectual Merit This laboratory study is aimed at characterizing the earthquake nucleation processes in fluid-saturated rock and directly contributes to Fault and Rupture Mechanics (FARM) working group research objectives. In addition, it is concerned with the issues pertaining to the role of pore fluids in time-dependent deformation, as well as the sensitivity of rock rheology and failure to applied stresses and pore pressures thus directly addressing the research priorities of Stress and Deformation Over Time (SDOT) working group.
Broader Impacts This project provided a partial support to one graduate student who has conducted the experiments on earthquake nucleation in fluid-saturated rock. Necessity for recording accurate microseismic data motivated modification of the laboratory acoustic emission equipment and algorithms. The obtained results will be disseminated at the upcoming SCEC annual meeting and AGU Fall meeting. Some of the datasets will be used by the students in rock mechanics and geoenergy courses taught by the PI. On the large scale, development of the constitutive laws for the inelastic time-dependent response of fluid-saturated rock should improve the predictability of hydromechanical models dealing with earthquake nucleation and precursory processes. The future work will involve establishing the relationships for fractured tight rock.
Exemplary Figure Figure 6. Summary of brittle creep experiments in terms of (a) sensitivity of the creep rate to the applied stress and (b) stress paths for creep stages. Failure envelope is measured during the conventional triaxial compression tests with constant deformation rate until the failure.