Testing the Utilization of a Seismic Network Outside the Main Mining Facility Area for Expanding the Microseismic Monitoring Coverage in a Deep Block Caving

Round 1

Reviewer 1 Report

The purpose is well understood for scientific research.　Ｈowever, there are no descriptopn of exavit locations and depth of the target site without any distance and depth clarification for all the figures. Therefore it is pretty hard to judge the scientific fact in the current form of the paper.

Author Response

Reviewer

The purpose is well understood for scientific research. However, there are no description of exavit locations and depth of the target site without any distance and depth clarification for all the figures. Therefore, it is pretty hard to judge the scientific fact in the current form of the paper.

Response to reviewer

We thank the reviewer for the constructive comment and questions. In this research, we applied a synthetic model. The synthetic model was built based on an extensive literature review of existing block caving available in the journal publication. We also gave special attention to the block caving model of PT Freeport Indonesia.  

Based on the literature review, we built a general model of block caving with the following notes:

1. The depth of the block caving is assumed to be around 2 km, which represents the average depth of existing deep mining. This information can be found in line 54-58 (introduction).
2. The cave in our synthetic model has an area of 50,000 m² in the abutment and a maximum height of 120 m. This represents a block caving at a depth of around 2 km which is growing vertically and abundant microseismic events would be observed in the abutment and the top cave. Therefore, imaging the velocity perturbation in the abutment and top cave becomes crucial.
3. The velocity perturbation in our synthetic model was set at 10% relative to the initial velocity model. This value represents the typical velocity perturbation observed in a typical deep mining with a depth of more than 1500 m [25,26].        

We update the description of the synthetic model after we received the comments from the reviewer in line 196-207 as follows:

We built a synthetic model with an incline intrusion geological setting with a slope of 490 consisting of three (3) different mining levels, the first mining level at an elevation of 1820 - 1880 mean sea level (msl), the second 1600 - 1680 msl, and the third at 1500 - 1560 msl (Figure 1). The depth of the block caving is 2000 m. Our abutment zone is set at an elevation of 1620 meters and the top cave is at an elevation of 1740 meters (Figure 3). Caving mine in this study was designed with a triangular pyramidal shape with cave heights varying from 10 meters on the one side and increasing gradually to a height of 120 meters on the other side (Figure 3). The abutment of the cave has an area of 50000 m². Our synthetic model represents a block caving that rises vertically. and abundant microseismic events would be observed in the abutment and the top cave. Therefore, imaging the velocity perturbation in the abutment and top cave is becoming crucial in monitoring the cave stability.

We also updated figures to represent the lateral distance and depth of the model better. The updated figures include: Figure 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12.

Reviewer 2 Report

Mining-induced stress is the origin of stress-induced failures, such as spalling, rockburst. Velocity tomography shows the potential to image the high mining-induced stress zones, and the basis for a successful velocity tomography is a good monitoring system and data analysis system, and the microseismic systems also an effective method for hazard early warning. In the paper “Testing the Utilization of a Seismic Network Outside the Main Mining Facility Area for Expanding the Microseismic Monitoring Coverage in a Deep Block Caving”, the authors conduct the seismometer deployment outside the mining facilities area with borehole seismometers to maximize the resolution and minimize the monitoring uncertainty of underground mines, they also create two scenarios for seismometer deployment. The Checkboard Resolution Test method was used to test their raypath responses and sensitivity. The authors proposed a good solution for the deployment of seismometers. But there are still many questions to be answered:

1 As we all know, a better microseismic system should cover the aimed zones and there are also many method for minimize the errors, so what is the advantage of your method?

2 The microseismic system errors affected by many factors, such as arrival picking method, location algorithms, background velocity, ray tracing method,etc. Raypath coverage is also an important factor because it was affect by seismeters number and location, events number and location, raytracing methods,but the raypath usually can be used to evaluate the resolution of velocity tomography, if fewer rays run through a voxel, we can consider the inversion result is not so reliable, I don’t know how can you use your method to minimize the monitoring uncertainty (such as location errors)? Is you method can improve the event location precision?

3 How do you generate the synthetic model?

4 The background velocity you used in your study is P-wave velocity of 5.6km/s, S-wave of 3.175m/s, do you think they are reliable? And do you consider surrounding rock are not always the same? I think it is better to consider actual background velocity

5 If the orebody was excavated, so many raypath can not run through these zones, so do you consider this question in your analysis?

6 The technical terms in the paper should be consistent, such as microseismic, microearthquake (line 401)

Author Response

Reviewer

Mining-induced stress is the origin of stress-induced failures, such as spalling, rockburst. Velocity tomography shows the potential to image the high mining-induced stress zones, and the basis for a successful velocity tomography is a good monitoring system and data analysis system, and the microseismic systems also an effective method for hazard early warning. In the paper “Testing the Utilization of a Seismic Network Outside the Main Mining Facility Area for Expanding the Microseismic Monitoring Coverage in a Deep Block Caving”, the authors conduct the seismometer deployment outside the mining facilities area with borehole seismometers to maximize the resolution and minimize the monitoring uncertainty of underground mines, they also create two scenarios for seismometer deployment. The Checkboard Resolution Test method was used to test their raypath responses and sensitivity. The authors proposed a good solution for the deployment of seismometers.

But there are still many questions to be answered:

1. As we all know, a better microseismic system should cover the aimed zones and there are also many method for minimize the errors, so what is the advantage of yourmethod?
2. The microseismic system errors affected by many factors, such as arrival picking method, location algorithms, background velocity, ray tracing method,etc. Raypath coverage is also an important factor because it was affect by seismeters number and location, events number and location, raytracing methods,but the raypath usually can be used to evaluate the resolution of velocity tomography, if fewer rays run through a voxel, we can consider the inversion result is not so reliable, I don’t know how can you use your method to minimize the monitoring uncertainty (such as location errors)? Is you method can improve the event location precision?
3. How do you generate the synthetic model?
4. The background velocity you used in your study is P-wave velocity of 5.6km/s, S-wave of 3.175m/s, do you think they are reliable? And do you consider surrounding rock are not always the same? I think it is better to consider actual background velocity
5. If the orebody was excavated, so many raypath can not run through these zones, so do you consider this question in your analysis?
6. The technical terms in the paper should be consistent, such as microseismic, microearthquake (line 401)

Response to reviewer

We appreciate the comments from the reviewer regarding the importance of an additional seismometer outside the main mining facilities for giving a better resolution of the microseismic monitoring. We performed two scenarios in this study to highlight the improvement brought by the additional seismometers. The stress perturbation in underground mining is very dynamic. Therefore, microseismic monitoring is becoming crucial for monitoring the stability of the cave. 

Following are our responses to the comments and questions from the reviewer:

1. In minimizing the error of the microseismic source parameters, including hypocenter locations, source magnitude, and mechanism, the station network must cover the seismic source. This is in the sense that the seismic network is deployed in almost all directions of the source location. However, in the case of inclined intrusion, the mining facility is only located in the footwall area. Therefore, there is a large azimuthal gap in uncovered microseisimic monitoring because the seismic network is only deployed from one side. In this study, we propose to install a borehole seismometer outside the facility area to increase the seismic network coverage. The good coverage will minimize the error of the source parameters as well as improve the resolution of the microseismic imaging.

The following description could be found in the introduction (lines 111-114):

To improve the coverage of the microseismic monitoring in the abutment and the seismogenic zone that is not covered by the typical seismometer network deployed in the facility area, we simulated the deployment of additional seismometers in the off-facilities area to maximize the resolution of the monitoring.

 

2. Yes, we agree with the reviewer that the raypath coverage is an important factor in determining the resolution of the microseismic monitoring. Our previous response to the reviewer has described the importance of adding the seismometer outside the main facility to increase the raypath coverage.

 

3. In general, the fewer ray crossing the voxel, the lower quality of the inversion results. The results suggest that the additional seismometer in the off-facilities area can increase the ray crossing the voxel and the resolution of the tomographic image by 30% in the seismogenic and abutment zone. We have mentioned this finding at the end of our abstract.

Yes, having a better station coverage could also improve the level of event precision. However, this is beyond the scope of this study. Therefore, we did not quantify the improvement of the hypocenter precision.

4. The synthetic model was built based on an extensive study literature of existing block caving available in the journal publication. Special attention was also given to the block caving model of PT Freeport Indonesia. Based on the study literature, we have built a general model of block caving with the following notes
   1. The depth of the block caving is assumed to be around 2 km depth, which represents the average depth of existing deep mining. This information can be found in lines 54-58 (introduction).
   2. The cave in our synthetic model has an area of 50.000 m2 in the abutment and a maximum height of 120 m. This represents a block caving at around 2 km depth which is growing vertically and abundant microseismic events would be observed in the abutment and the top cave. Therefore, imaging the velocity perturbation in the abutment and top cave is becoming crucial.
   3. The velocity perturbation in our synthetic model was set at 10% relative to the initial velocity model. This value represents the typical velocity perturbation observed in typical deep mining with the depth of more than 1500 m [25,26].

The description of the synthetic model is presented in lines 196-207.

We built a synthetic model with an incline intrusion geological setting with a slope of 490 consisting of three (3) different mining levels, the first mining level at an elevation of 1820 - 1880 mean sea level (msl), the second 1600 - 1680 msl, and the third at 1500 - 1560 msl (Figure 1). The depth of the block caving is 2000 m. Our abutment zone is set at an elevation of 1620 meters and the top cave is at an elevation of 1740 meters (Figure 3). Caving mine in this study was designed with a triangular pyramidal shape with cave heights varying from 10 meters on the one side and increasing gradually to a height of 120 meters on the other side (Figure 3). The abutment of the cave has an area of 50000 m². Our synthetic model represents a block caving that rises vertically. and abundant microseismic events would be observed in the abutment and the top cave. Therefore, imaging the velocity perturbation in the abutment and top cave is becoming crucial in monitoring the cave stability.

5. Yes, we consider that if the rock was excavated, the raypath could not cross through these zones. The visualization of the raypath avoiding the excavated zone is presented in Figure 6.

 

6. We thank the reviewer for the constructive suggestion. For consistency purposes, the technical term “microseismic” is used throughout the manuscript.

Reviewer 3 Report

The paper deals with the seismometer deployment outside the mining facilities area with borehole seismometers with the goal of maximizing the resolution. Two scenarios were employed by seismometers deployed following the intrusion mining level in the mining facility area in addition to additional seismometers deployed in off-facilities areas.

 The paper is well-written and English is good enough. It is easy to follow and the results are presented in terms of clear figures. The paper contains enough novelty to be published in the Journal, and it offers interesting results to the research community. Thereby, it is recommended to be published after a thorough check of English grammar of the whole manuscript.

 The authors are also advised to provide some information/discussion on the type and precision of the seismometers employed in their study. How the outcomes of this research may be affected by the accuracy of the measurement in terms of the seismometer type?

Author Response

Reviewer

The paper deals with the seismometer deployment outside the mining facilities area with borehole seismometers with the goal of maximizing the resolution. Two scenarios were employed by seismometers deployed following the intrusion mining level in the mining facility area in addition to additional seismometers deployed in off-facilities areas.

The paper is well-written and English is good enough. It is easy to follow and the results are presented in terms of clear figures. The paper contains enough novelty to be published in the Journal, and it offers interesting results to the research community. Thereby, it is recommended to be published after a thorough check of English grammar of the whole manuscript.

 The authors are also advised to provide some information/discussion on the type and precision of the seismometers employed in their study.

Response to reviewer

We thank the reviewer for the very positive comments. We highlight the importance of adding seismometers outside the mining facilities through the two scenarios we performed in this research.

As suggested by the reviewer, we thoroughly checked the English grammar of the whole manuscript.

We thank the reviewer for the comments on the type of the suggested seismometers to be deployed outside the main facility.  We suggest using a combination of broadband and short period 4.5 Hz borehole seismometer for having a high resolution required in a very local scale of underground mining case. This suggestion is added at the end of the conclusion in lines 408-410

We suggest that the borehole seismometers deployed outside the main facility consist of broadband and short period 4.5 Hz seismometers with sampling rates higher than 4 KHz.