Research Article: Targeted location of microseismic events based on a 3D heterogeneous velocity model in underground mining

Date Published: February 25, 2019

Publisher: Public Library of Science

Author(s): Pingan Peng, Liguan Wang, Peitao Wang.

http://doi.org/10.1371/journal.pone.0212881

Abstract

The accurate location of induced seismicity is a problem of major interest in the safety monitoring of underground mines. Complexities in the seismic velocity structure, particularly changes in velocity caused by the progression of mining excavations, can cause systematic event mislocations. To address this problem, we present a novel construction method for an arbitrary 3D velocity model and a targeted hypocenter determination method based on this velocity model in underground mining. The method constructs a velocity model from 3D geological objects that can accurately express the interfaces of geologic units. Based on this model, the block corresponding to the minimum difference between the observed arrival times and the theoretical arrival times computed by the Fast Marching Method is located. Finally, a relocation procedure is carried out within the targeted block by heuristic algorithms to improve the performance. The accuracy and efficiency of the proposed method are demonstrated by the source localization results of both synthetic data and on-site data from Dongguashan Copper Mine. The results show that our proposed method significantly improves the location accuracy compared with the widely used Simplex and Particle Swarm Optimization methods.

Partial Text

Microseismic monitoring is becoming a common tool with wide and successful applications in mining engineering [1]. It can provide important insight into a rock mass and quantify where a certain magnitude of induced rock fracturing is occurring within the volume [2]. Of the many processing procedures, event localization is crucial for the successful application of microseismic monitoring.

In this section, we conduct a series of synthetic tests to demonstrate the accuracy and efficiency of the proposed method.

The Dongguashan Copper Mine is located in Tongling, Anhui Province, China. Because it is a deep underground mine, Dongguashan suffers from rockburst hazards that can result in casualties and damage to equipment. Therefore, a microseismic monitoring system was installed in Dongguashan with 7 accelerators embedded at the -730 m level and the -790 m level. The coordinates of these receivers are listed in Table 4, and the layout is shown in Fig 9. Microseismic events were processed using commercial software by analysts in daily monitoring. The constant velocity used in processing is 5730 m/s, which is calibrated by blasts with known coordinates. The distance from the blast to each of the sensors is calculated and plotted against the absolute or relative arrival time recorded on the seismic system. Then the velocity is simply the slope of the best-fit line. According to the report by Dongguashan Copper Mine, location accuracy by traditional methods turned out to be poor. As we known, locating induced seismicity in active underground mines is a challenging problem because of the presence of complex structures, such as mined-out goafs, filled stopes and rock strata. As demonstrated above, we can construct an arbitrary 3D velocity model and accurately locate events using this model with our method. By considering the velocity inhomogeneity, the proposed method provides better location quality than traditional methods. To validate this, controlled blast experiments with small amounts of explosives were carried out in five different locations in the monitoring area.

We present a novel construction method for an arbitrary 3D velocity model and a targeted hypocenter determination method based on this velocity model in underground mining. The method constructs the velocity model by converting 3D geological objects that accurately express the interfaces of realistic geology. Based on this model, the block corresponding to the minimum difference between the observed arrival times and the theoretical arrival times computed by the FMM method is located. Finally, a relocation procedure is carried out within the targeted block to improve the location accuracy. We successfully tested this approach with both synthetic and field-data applications in underground mining. The results show that the methodology can greatly improve the location accuracy compared to the Simplex and PSO methods in heterogeneous media. It should be noted that accurate velocity structures are a prerequisite for reducing the location errors and need to be obtained through other geophysical methods, which is not a focus of this paper.

 

Source:

http://doi.org/10.1371/journal.pone.0212881

 

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