## 2 Specimens and Experimental Setup  
This paper focus on the results of three experiments conducted on intact (SA) or pre-cut (S1 and S2) cylindrical specimens 50 mm in diameter and 125 mm in length. These specimens were cored from a single granite block. The rock block is a homogeneous and fine-grained granite, which shows very weak anisotropy and low density of pre-existing microcracks [12]. The pre-cut surface had an angle of 45\({}^{\circ}\) with respect to the axis, which is the direction of the greatest principal stress under the experimental conditions. All specimens were naturally dried under ambient conditions. The fine-grained granite had a relatively low density of pre-existing microcracks, as indicated by the high P-wave velocity of approximately 6.0 km/s. The results for an intact specimen were used for reference and for estimating fault slip in the pre-cut specimens. The typical range for the frictional coefficient for faults in the upper crust is 0.6 to 0.75. The early results of the present study, including data for specimens pre-cut at 50\({}^{\circ}\), showed that the friction coefficient for the pre-cut faults in the granite specimens does not depend on the fault angle, but drops from approximately 0.75 to 0.6 after a few stick-slip iterations [12], and falls within the typical range in the upper crust. Based on the Mohr-Coulomb failure criteria, the optimal angle between the fault plane and the maximum principal stress axis is approximately 25\({}^{\circ}\)-30\({}^{\circ}\). The primary results show that the pre-cut faults in our test specimens were deemed to be unfavorably oriented, and their friction strength is expected to be 50% greater than that for an optimally oriented fault [12].  
The roughness of the pre-cut surfaces was measured using a laser scanner. As shown in Figure 1, the power spectral density function follows a power law: \(S_{v}(f)\propto\lambda^{\beta}=\frac{1}{f^{\beta}}\). Thus, the generalized Hurst exponent (\(H\), [0, 1]) and the fractal dimension (\(D\)) can be determined, because these parameters are correlated with each other: \(\beta=2H+1\) and \(D=\mathrm{d}+1-H\). The estimated fractal dimension along the dip direction (slip direction during the experiment) was 1.30, and that for strike direction was 1.55. Since the fractal features of the fault surface are key to the similarity (scale independence) between faults of different size, the pre-cut specimens used in the present study can be considered to be an analogue of natural faults.  
The loading and AE monitoring systems used in the present study were similar to those used in previous studies [13]. First, specimens were hydrostatically compressed by gradually increasing the confining pressure to 40 MPa. The axial load was then increased at a rate of 10 MPa/min, while the confining pressure was kept constant. In our loading system, the axial force is balanced by a spring, which is simply compressed by a stepping motor. After a stress drop, the force of the spring does not change, so the reloading speed is very fast (5.5 MPa/s), and the time interval between two consecutive stick-slip events is a few tens of seconds. Thus, time-dependent healing can be ignored.