## 3 Results  
### Cases of Different Pressurization Rates  
The evolution of the shear stress \(\tau\), effective normal stress \(\sigma_{n}t\), injection pressure \(p\), slip distance \(d_{s}\), slip rate \(v_{s}\), and water injection volume under the different pressurization rates is shown in Figure 4. To study the effect of pressurization rate, four tests were conducted at the same initial stress state (\(\sigma_{n}t\approx 13.5\) MPa, \(\tau\approx 8.5\) MPa). According to the four slip distance curves in the figure, the fault remained locked (slip distance \(\approx 0\)) in the initial of water injection. According to the yellow circle in Figure 4a, at a pressurization rate = 0.5 MPa/min, fault slip onset (slip distance curve appears and shear stress began to go down) was detected at \(p\) = 3.08 MPa. As the pressurization rate increased, so did the injection pressure required for fault slip initiation, which was 4.57 MPa, 4.95 MPa, and 6.01 MPa, respectively (Figure 4a-c). At 0.5 MPa/min, as the injection pressure increased, the fault continued to slip at a rate of no more than 1 \(\upmu\)m/s, and the effective normal stress and shear stress decreased linearly with the slip. The whole process resembled quasi-static slip (Figure 4a), as no locked phase appeared after slip initiation. In contrast, the slip process under higher pressurization rates (2 MPa/min, 8 MPa/min, and 32 MPa/min) showed a high peak slip rate (>15 \(\upmu\)m/s), indicating that a dynamic slip appeared and was accompanied by a sharp drop in shear stress and effective normal stress (Figure 4b-d). At the higher pressurization rate of 8 MPa/min, the slip process underwent two dynamic slip phases, and the peak slip rates of the two dynamic slips reached 15.57 \(\upmu\)m/s and 59.89 \(\upmu\)m/s, respectively, which were \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Test No.**} & **Pressurization Rate (MPa/min)** & **Confining Pressure (MPa)** & **Inclination Angle (\({}^{\circ}\))** & **Shear Strength (MPa)** & **Critical** & **Slip** & **Peak Slip Distance \(d_{s}\)** & **Rate \(v_{s}\)** \\  & **Rate (MPa/min)** & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **(\(\upmu\)m)** & **(\(\upmu\)m/s)** \\ \hline Z1 & 0.5 & 10 & 60 & 9.26 & 0.9 \(\tau_{s}\) & 226.89 & 0.84 \\ Z2 & 2 & 10 & 60 & 9.57 & 0.9 \(\tau_{s}\) & 198.14 & 30.95 \\ Z3 & 8 & 10 & 60 & 9.59 & 0.9 \(\tau_{s}\) & 227.9 & 59.89 \\ Z4 & 32 & 10 & 60 & 9.35 & 0.9 \(\tau_{s}\) & 213.8 & 64.6 \\ W2 & 2 & 20 & 60 & 17.59 & 0.9 \(\tau_{s}\) & 142 & 1.91 \\ W3 & 2 & 30 & 60 & 28.99 & 0.9 \(\tau_{s}\) & 52.88 & 1.03 \\ J1 & 2 & 10 & 45 & 19.87 & 0.9 \(\tau_{s}\) & 253 & 10.08 \\ J2 & 2 & 10 & 45 & 19.01 & 0.85 \(\tau_{s}\) & 109 & 12.68 \\ J3 & 2 & 10 & 45 & 18.23 & 0.80 \(\tau_{s}\) & 21.53 & 14.70 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of experimental conditions and partial results. Figure 3: Diagram of the whole load path including the following: displacement-driven shear test (Stage 1), unloading (Stage 2), and injection-driven shear test (Stage 3), performed at pressurization rates of 0.5 MPa/min, \(\sigma_{3}\) = 10 MPa, and an inclination angle \(\psi\) = 30\({}^{\circ}\). accompanied by two shear stress drops of 0.4 MPa and 0.64 MPa each (Figure 4c). Between the two dynamic slips, a fault locked phase was detected, which indicated that the fault stopped slipping. This embodied an obvious stick-slip characteristic. At 32 MPa/min, the highest slip rate of 64.6 \(\upmu\)m/s was detected among the four tested pressurization rates (Figure 4d). Cumulative slip distances under four conditions were similar, at approximately 0.2 mm, but the methods of cumulation are different. Under low pressurization rates (0.5 MPa/min and 2 MPa/min), cumulation occurred through slow slip over a long period of time. In contrast, rapid slip over a short period of time caused the cumulation of the slip distance when the pressurization rate was high.