To investigate mechanisms causing microseismicity (M_w < 2) at a CO₂ injection site, a large-scale triaxial block experiment was carried out on a faulted (saw-cut) cubic-meter of Castlegate Sandstone. The experiment consisted of injection tests at varying differential stresses, while monitoring and recording pore pressure and acoustic emissions (AEs). During the experiment, ∼33,000 AEs and ∼14 mm of horizontal displacement/slip, like a strike-slip fault movement, occurred. To understand the AE responses and ascertain fault characteristics near the located AEs, we modeled the topography of the fault surface, fault aperture, and fault-gouge thickness using pre- and post-experiment laser scans of the fault surface on each half of the block. Additionally, we characterized surface roughness parallel and perpendicular to slip. Models show crushing and flattening of the fault surfaces can be linked to the spatiotemporal distribution of AEs within 50 mm of the fault surface. Approximately 65% of AEs were in areas with small aperture (≤300 μm); thicker fault gouge was observed in adjacent areas with wider aperture and shows a two-fold reduction in grain size relative to unaltered Castlegate Sandstone. This work provides a conceptual understanding on fault surface evolution, which can be applied towards modeling of seismic slip.

 研究在 CO ₂下引起微震 (M _{w < 2) 的机制}在注入现场，对一个断层（锯切）立方米的 Castlegate 砂岩进行了大规模的三轴块试验。该实验包括在不同不同应力下的注入测试，同时监测和记录孔隙压力和声发射 (AE)。在实验过程中，发生了~33,000 次AEs 和~14 mm 的水平位移/滑动，就像走滑断层运动一样。为了了解 AE 响应并确定定位的 AE 附近的断层特征，我们对断层的地形、断层孔径和断层泥厚度使用实验前和实验后对块体每一半断面的激光扫描进行了建模. 此外，我们表征了平行和垂直于滑动的表面粗糙度。模型显示断层表面的破碎和变平可能与断层表面 50 毫米内 AE 的时空分布有关。大约 65% 的 AE 位于小孔径（≤300 μm）区域；在具有更宽孔径的相邻区域观察到更厚的断层泥，并且相对于未改变的 Castlegate 砂岩，粒度减小了两倍。这项工作提供了对断层表面演化的概念理解，可应用于地震滑动的建模。