Experimental Study on the Seismic Behavior of Fault Gouge under Changing Pore Pressures

Abstract:

Understanding the effect of changing pore pressure on fault gouge seismic behavior is crucial in the assessment of tectonic and induced seismicity, especially in the context of subsurface technologies like wastewater disposal, hydraulic fracturing, oil and gas production, geothermal energy extraction, and geologic storage of carbon dioxide (National Research Council, 2013).

While the effect pressurization rate on induced seismicity of rough surfaces (e.g., Wang 2020) and fault gouge (e.g., Scuderi and Collettini, 2018) has been studied before, here we aim to overcome limitations in the amount of shear strain that can be achieved in triaxial tests, and the difficulties in controlling pore pressure in direct shear tests. To do so, we designed a novel experimental setup configured as a ring shear apparatus to enable large shear strain, normal stress and pore pressure control, and visual observations. This setup is used to study the seismic vs. aseismic behavior of fault gouge under changing pore pressures.

Here, we use glass beads as analogue material for weakly-consolidated fault gouge, and study the induced seismic activity under different pressurization rates. The results share many similarities with induced earthquakes, and shed light into how the pressurization rates affect the slip dynamics, providing the basis for novel constitutive modeling of fault friction.