Group B, Poster #148, Stress and Deformation Over Time (SDOT)

Correlation between creep and acoustic emission during earthquake preparation

Nikita Bondarenko, Roman Y. Makhnenko, & Yury Y. Podladchikov
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Poster Presentation

2023 SCEC Annual Meeting, Poster #148, SCEC Contribution #13229 VIEW PDF
The processes occurring during the earthquake preparation and nucleation cannot be captured by elastic- perfectly plastic constitutive models that neglect features of material behavior at subcritical stress. Additional work is required to take into account the role of transient and time-dependent processes, inelastic deformation, as well as the mechanical and chemical effects of pore fluids and fluid transport. Within the scope of this work, laboratory experiments on brittle creep behavior are conducted 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 c...onditions. High correlation between low-temperature high-stress creep deformation and acoustic emission is observed, highlighting the potential for prognostic features of deformation localization in microcracking activity. Significant variations of b-value in magnitude-frequency relation during macroscopic failure preparation is observed independently of experimental conditions, making this parameter potentially suitable as a prognostic feature of earthquake preparation process. The presence of non-aqueous fluid (oil or CO2) appears to have significantly weaker impact on the promotion of creep deformation compared to aqueous fluids. Additionally, dilatant hardening is observed during the preparation of macroscopic failure in the experiments where fluid drainage is prohibited, which might be relevant to processes occurring in the off-fault plasticity zone. Finally, the collected data on time-dependent deformation is interpreted by introducing viscosity as a coefficient of proportionality between deviatoric strain rate and applied deviatoric stress. It appears that viscosity is exponentially decreasing when the state of stress is approaching critical conditions associated with macroscopic failure. The conducted experiments allow to establish relationship that describes the impact of mean and deviatoric stress on viscosity in wide range of applied stress that is relevant to material behavior during earthquake nucleation.