## 4 Discussion  
Stress accumulation in underground mines generally occurs in the abutment and seismogenic zones [10]. High stress concentrations in the abutment and seismogenic zones are caused by the extraction of rock mass using the caving method [11]. In the case of an inclined intrusion, the stress in the rock mass in the hanging wall is also induced by the adjacent cave. Should the induced stress be extremely high, the rock mass can collapse, which can affect the direction of cave propagation. Uncontrolled cave propagation can result in an overbreak in the lithological boundary. This is not desirable, as it will cause mixing of high-grade ore with low-grade ore (dilution). To determine the risk of this possibility, it is necessary to monitor the seismogenic zone. Monitoring of stress distribution and cave propagation in this zone is necessary to map the zones that are vulnerable to seismic activity. Therefore, it can reduce the potential risk of seismic hazard in underground mines. In general, the results for the checkerboard inversion show that there are differences in the recovered zones and the zones not covered in each scenario where the ray coverage is relatively consistent in the center area of the model. The results of the Vp and Vs CRT inversions show the dominant resolution coverage to be in the northeast-southwest direction, following the event and station distribution (Figures 7 and 8). According to the results of the Vp and Vs inversion tomograms with the scenario following the facility, the abutment zone is depicted in the area to the southeast of the caving, while the northwest side is not covered (Figures 6(a) and 6(a)). The abutment zone on the northwest side is not covered due to the absence of a raypath as a consequence of the absence of a seismometer station. The raypath direction of the earthquake cluster in the northeast abutment zone becomes indistinct towards the station (northeast-southwest), which implies that the area cannot be interpreted (Figure 6(a)). To gain an overview of the abutment zone in the northwest area, a simulation of the deployment of a seismometer borehole in the off-facilities area was conducted in this study. The positioning and procedure for placing seismometers in off-facilities areas have been described in the introduction. Tomograms of Vp and Vs in the scenario of adding a borehole seismometer in the off-facilities area are shown in Figures 6(b) and 6(b). Additional borehole seismometers in the northwest area were deployed at elevations of 1560 and 1740 msl to cover the abutment and seismogenic zone. The addition of this borehole seismometer resulted in a better raypath distribution (Figure 6(b)). Figure 6(b) shows that the raypath not only leads to one side (northeast-southwest), but also covers the northwest area. Figure 9 shows the difference in the area recovered for the Vp tomogram. The area outside the cave, which is the abutment zone, can be interpreted properly by adding a seismometer to the northwest area. The area that can be interpreted through the addition of the borehole seismometer network is 30% wider than the initial area. The Vs tomogram (Figure 10)shows the same thing as the Vp tomogram, but the recovered area is not as wide as the Vp tomogram; this is caused by a difference in the number of data. The abutment zones in the northeast and northwest are areas of stress concentration due to caving and incline intrusion geological settings, according to the conceptual model of [PERSON], (2001); [PERSON], (2004). According to the caving model described above, in the stress concentration zone there is a seismogenic zone where seismic events occur (Figure 3). The shift of events in the seismogenic zone is an indicator of the cave propagation process. Therefore, the seismometer network coverage has an important role in the monitoring of events, especially in zones with seismic potential.