scholarly journals Tomographic Experiments for Defining the 3D Velocity Model of an Unstable Rock Slope to Support Microseismic Event Interpretation

Geosciences ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 327
Author(s):  
Zhiyong Zhang ◽  
Diego Arosio ◽  
Azadeh Hojat ◽  
Luigi Zanzi
Keyword(s):  
Rock Mass ◽  
Velocity Distribution ◽  
Velocity Model ◽  
Microseismic Monitoring ◽  
Time Inversion ◽  
Basic Step ◽  
Rock Face ◽  
3D Velocity Model ◽  
Microseismic Events ◽  
The Stability

To monitor the stability of a mountain slope in northern Italy, microseismic monitoring technique has been used since 2013. Locating microseismic events is a basic step of this technique. We performed a seismic tomographic survey on the mountain surface above the rock face to obtain a reliable velocity distribution in the rock mass for the localization procedure. Seismic travel-time inversion showed high heterogeneity of the rock mass with strong contrast in velocity distribution. Low velocities were found at shallow depth on the top of the rock cliff and intermediate velocities were observed in the most critical area of the rock face corresponding to a partially detached pillar. Using the 3D velocity model obtained from inversion, localization tests were performed based on the Equal Differential Time (EDT) localization method. The results showed hypocenter misfits to be around 15 m for the five geophones of the microseismic network and the error was significantly decreased compared to the results produced by a constant velocity model. Although the localization errors are relatively large, the accuracy is sufficient to distinguish microseismic events occurring in the most critical zone of the monitored rock mass from microseismic events generated far away. Thus, the 3D velocity model will be used in future studies to improve the classification of the recorded events.

scholarly journals Reclassification of Microseismic Events through Hypocenter Location: Case Study on an Unstable Rock Face in Northern Italy

Geosciences ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 37
Author(s):  
Zhiyong Zhang ◽  
Diego Arosio ◽  
Azadeh Hojat ◽  
Luigi Zanzi
Keyword(s):  
Rock Mass ◽  
Northern Italy ◽  
Quality Data ◽  
Basic Step ◽  
Rock Face ◽  
Hypocenter Location ◽  
3D Velocity Model ◽  
Microseismic Events ◽  
Unstable Rock

Passive seismic methods are increasingly used in monitoring unstable rock slopes that are likely to cause rockfalls. Event classification is a basic step in microseismic monitoring. However, the classification of events generated by the propagation of fractures and rockfalls is still uncertain due to their similar features in the time and frequency domains. Hypocenter localization might be a powerful tool to distinguish events generated by fracture propagation from those caused by rockfalls. In this study, a classification procedure based on hypocenter location was validated using a selected subset of high-quality data recorded by a five-geophone network installed on a steep rock slope in Northern Italy. Considering the complexity and heterogeneity of the rock mass, a 3D velocity model that was derived from a tomographic experiment was used. We performed the localization using the equal differential time method. The location results fairly fit our expectations on suspected rockfall events because most signals were located near the rock face. However, only 4 out of 20 suspected fracture events were unquestionably confirmed as fractures being located inside the rock mass and far enough from the rock face. Further improvements in location accuracy are still necessary to distinguish suspected fracture events located close to the rock face from rockfalls. This study demonstrates that hypocenter location is a promising method to improve the final classification of microseismic events.

scholarly journals Automatic Classification of Microseismic Signals Based on MFCC and GMM-HMM in Underground Mines

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Pingan Peng ◽  
Zhengxiang He ◽  
Liguan Wang
Keyword(s):  
Rock Mass ◽  
Gaussian Mixture ◽  
Automatic Classification ◽  
Microseismic Monitoring ◽  
Underground Mines ◽  
Basic Step ◽  
Microseismic Data ◽  
Safety Risks ◽  
Microseismic Events

In order to mitigate economic and safety risks during mine life, a microseismic monitoring system is installed in a number of underground mines. The basic step for successfully analyzing those microseismic data is the correct detection of various event types, especially the rock mass rupture events. The visual scanning process is a time-consuming task and requires experience. Therefore, here we present a new method for automatic classification of microseismic signals based on the Gaussian Mixture Model-Hidden Markov Model (GMM-HMM) by using only Mel-frequency cepstral coefficient (MFCC) features extracted from the waveform. The detailed implementation of our proposed method is described. The performance of this method is tested by its application to microseismic events selected from the Dongguashan Copper Mine (China). A dataset that contains a representative set of different microseismic events including rock mass rupture, blasting vibration, mechanical drilling, and electromagnetic noise is collected for training and testing. The results show that our proposed method obtains an accuracy of 92.46%, which demonstrates the effectiveness of the method for automatic classification of microseismic data in underground mines.

Evolution of a block cave from time-lapse passive source body-wave traveltime tomography

Geophysics ◽  
2015 ◽  
Vol 80 (2) ◽  
pp. WA85-WA97 ◽  
Author(s):  
Jean-Philippe Mercier ◽  
Willem de Beer ◽  
Jean-Pascal Mercier ◽  
Simon Morris
Keyword(s):  
Rock Mass ◽  
Velocity Distribution ◽  
Body Wave ◽  
Time Lapse ◽  
Microseismic Monitoring ◽  
Monitoring Systems ◽  
Simultaneous Estimation ◽  
Velocity Models ◽  
Microseismic Events ◽  
Microseismic Event

Most underground mines are equipped with microseismic monitoring systems that allow the detection, location, and characterization of microseismic events. Microseismic events can be exploited to understand the rock mass response to mining. However, seismicity provides information only for regions that are seismically active. Although some information on nonseismically active regions can be obtained from point measurements and numerical modeling, these methods suffer from limitations of their own. Passive source traveltime body-wave tomography (passive source tomography [PST]) uses information readily collected by microseismic monitoring systems, namely, the P- and/or S-wave traveltimes and microseismic event hypocenter locations. This technique allowes the simultaneous estimation of the velocity distribution between sensors and microseismic events and the correction of microseismic event hypocenter locations. In this paper, we present an application of time-lapse PST to the Northparkes Mines E26 Lift 2 block cave showing that PST can be used to obtain information on evolution and distribution of seismic velocities, leading to a better understanding of stress distribution and redistribution and of rock mass behavior during the development and production phases. In particular, we found that (1) the magnitude of the velocity perturbation varied through time and appeared to be strongly correlated with the intensity of microseismic activity, the mining rate, and the nature of the mining activity, (2) the velocity models provided information that allowed for the inference of the cave geometry and its evolution through time, (3) the stress distributions inferred from the velocity model were not fully consistent with a widely accepted conceptual stress redistribution model, which may reflect the significant influence of rock mass inhomogeneities and the mining sequence, (4) seismicity was found in regions in which velocity was higher and lower than the background velocity, and (5) there was no obvious correlation between geology and velocity distribution and evolution.

scholarly journals Stability Evaluation on Surrounding Rocks of Underground Powerhouse Based on Microseismic Monitoring

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Feng Dai ◽  
Biao Li ◽  
Nuwen Xu ◽  
Yongguo Zhu ◽  
Peiwei Xiao
Keyword(s):  
Rock Mass ◽  
Microseismic Monitoring ◽  
Surrounding Rock ◽  
Underground Powerhouse ◽  
Multiple Faults ◽  
Routine Monitoring ◽  
Underground Caverns ◽  
Macroscopic Deformation ◽  
Microseismic Events ◽  
The Stability

To study the stability of underground powerhouse at Houziyan hydropower station during excavation, a microseismic monitoring system is adopted. Based on the space-time distribution characteristics of microseismic events during excavation of the main powerhouse, the correlation between microseismic events and blasting construction is established; and the microseismic clustering areas of the underground powerhouse are identified and delineated. The FLAC3D code is used to simulate the deformation of main powerhouse. The simulated deformation characteristics are consistent with that recorded by microseismic monitoring. Finally, the correlation between the macroscopic deformation of surrounding rock mass and microseismic activities is also revealed. The results show that multiple faults between 1# and 3# bus tunnels are activated during excavation of floors V and VI of the main powerhouse. The comprehensive method combining microseismic monitoring with numerical simulation as well as routine monitoring can provide an effective way to evaluate the surrounding rock mass stability of underground caverns.

Results of the downhole microseismic monitoring at a pilot hydraulic fracturing site in Poland — Part 1: Event location and stimulation performance

2018 ◽  
Vol 6 (3) ◽  
pp. SH39-SH48 ◽  
Author(s):  
Wojciech Gajek ◽  
Jacek Trojanowski ◽  
Michał Malinowski ◽  
Marek Jarosiński ◽  
Marko Riedel
Keyword(s):  
Hydraulic Fracturing ◽  
Seismic Anisotropy ◽  
Transverse Isotropy ◽  
Velocity Model ◽  
Microseismic Monitoring ◽  
Baltic Basin ◽  
Hydraulic Stimulation ◽  
Lower Paleozoic ◽  
Event Location ◽  
Microseismic Events

A precise velocity model is necessary to obtain reliable locations of microseismic events, which provide information about the effectiveness of the hydraulic stimulation. Seismic anisotropy plays an important role in microseismic event location by imposing the dependency between wave velocities and its propagation direction. Building an anisotropic velocity model that accounts for that effect allows for more accurate location of microseismic events. We have used downhole microseismic records from a pilot hydraulic fracturing experiment in Lower-Paleozoic shale gas play in the Baltic Basin, Northern Poland, to obtain accurate microseismic events locations. We have developed a workflow for a vertical transverse isotropy velocity model construction when facing a challenging absence of horizontally polarized S-waves in perforation shot data, which carry information about Thomsen’s [Formula: see text] parameter and provide valuable constraints for locating microseismic events. We extract effective [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text] for each layer from the P- and SV-wave arrivals of perforation shots, whereas the unresolved [Formula: see text] is retrieved afterward from the SH-SV-wave delay time of selected microseismic events. An inverted velocity model provides more reliable location of microseismic events, which then becomes an essential input for evaluating the hydraulic stimulation job effectiveness in the geomechanical context. We evaluate the influence of the preexisting fracture sets and obliquity between the borehole trajectory and principal horizontal stress direction on the hydraulic treatment performance. The fracturing fluid migrates to previously fractured zones, while the growth of the microseismic volume in consecutive stages is caused by increased penetration of the above-lying lithologic formations.

Establishment and Application of Microseismic Monitoring System to Deep-Buried Underground Powerhouse

2013 ◽  
Vol 838-841 ◽  
pp. 889-893
Author(s):  
Biao Li ◽  
Feng Dai ◽  
Nu Wen Xu ◽  
Chun Sha
Keyword(s):  
Rock Mass ◽  
Monitoring System ◽  
Wave Velocity ◽  
Microseismic Monitoring ◽  
Surrounding Rock ◽  
P Wave ◽  
Monitoring Method ◽  
Underground Powerhouse ◽  
Geological Conditions ◽  
The Stability

The right bank underground powerhouse of Houziyan hydropower station is a typical deep-buried type with high geostress and complicated geological conditions. To monitor and analyze the stability of surrounding rock mass during continuous excavation of the powerhouse excavation and locate the potential failure zones, an ESG (Engineering Seismology Group) microseismic monitoring system manufactured in Canada was installed in April, 2013. The wave velocity of the monitoring system was determined through fixed blasting tests. And the average location error is the minimum while P-wave velocity is 5700m/s, less than 10m and meeting the system request. By combining the temporal and spatial distribution regularity of microseimic events with field excavation, micro-crack clusters and potential instability zones were identified and delineated. The results will provide a reference for later excavations and supports of the underground powerhouse. Furthermore, a new monitoring method can also be supplied for the stability analysis of surrounding rock mass in deep-buried underground powerhouses.

scholarly journals Rock Fracture Monitoring Based on High-Precision Microseismic Event Location Using 3D Multiscale Waveform Inversion

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Yi Wang ◽  
Xueyi Shang ◽  
Kang Peng ◽  
Rui Gao
Keyword(s):  
Rock Mass ◽  
Fractional Order ◽  
Waveform Inversion ◽  
Velocity Model ◽  
Time Function ◽  
Source Time Function ◽  
Fracture Characteristics ◽  
3D Velocity Model ◽  
Study Results ◽  
Event Location

Microseismic (MS) source location can help us obtain the fracture characteristics of a rock mass under a thermal-hydraulic-mechanical (THM) coupling environment. However, the commonly used ray-tracing-based location methods are easily affected by the large picking errors, multipath effects of travel time, and focusing and defocusing effects of rays in wavefield propagation, which are caused by the strong three-dimensional (3D) heterogeneity in mining areas. In this paper, we will introduce the rapidly developed waveform inversion-based location method into a mine MS field study. On this basis, the wavefields were modeled by utilizing a high-resolution 3D velocity model, a fractional-order Gaussian wavelet source-time function, and spectral element method (SEM) wavefield modeling. In order to reduce the computation cost of wavefield modeling, the 3D ray-shooting method based on a coarse grid was adopted to obtain an approximate MS event location. Based on this initial location, the multiscale waveform inversion strategy (from coarse to fine grids) and the L-BFGS iteration optimization algorithm were separately jointly selected to improve wavefield modeling speed efficiency and iterative convergence rate. Then, the IMS MS monitoring system set in the Yongshaba mine (China) and its tomographic 3D velocity model were used to conduct the synthetic test and application study. Results show that the source-time function based on the fractional-order Gaussian function wavelet can better fit complex recording waveforms compared with the conventional Ricker wavelet-based source-time function, and the waveform misfit during the L-BFGS iteration decreased rapidly. Furthermore, the multiscale waveform inversion method can obtain a similar location accuracy compared with the waveform inversion based on a single fine grid, and it can significantly decrease the iteration times and wavefield modeling computational cost. The average location error of the eight premeasured blasting events by the proposed approach is only 17.6 m, which can provide a good data research basis for analyzing MS event location and rock mass fracture characteristics in a mine.

Comparing traditional geomechanical and remote sensing techniques for rock mass characterization 

2021 ◽  
Author(s):  
Angela Caccia ◽  
Biagio Palma ◽  
Mario Parise
Keyword(s):  
Rock Mass ◽  
Point Cloud ◽  
Laser Scanning ◽  
Quantitative Description ◽  
Present Contribution ◽  
Rock Mass Characterization ◽  
Rock Face ◽  
Remote Sensing Techniques ◽  
The Stability ◽  
Processing Techniques

<p>Analysis of the stability conditions of rock masses starts from detailed geo-structural surveys based on a systematic and quantitative description of the systems of discontinuities. Traditionally, these surveys are performed by implementing the classical geomechanical systems, available in the scientific literature since several decades, through the use of simple tools such as the geological compass to measure dip and dip direction directly on the discontinuity systems, and to fully describe their more significant physical characteristics (length, spacing, roughness, persistence, aperture, filling, termination, etc.). In several cases, this can be difficult because the discontinuities, or even the rock face, cannot be easily accessible. To have a complete survey, very often the involvement of geologists climbers is required, but in many situations this work is not easy to carry out, and in any case it does not cover the whole rock front.</p><p>Today, to solve these problems, traditional geomechanical surveying is implemented by innovative remote techniques using, individually or in combination, instruments such as terrestrial laser scanners and unmanned aerial vehicles to build a point cloud.</p><p>This latter permits to extract very accurate data on discontinuities for stability analyses, based on areal and non-point observations. In addition, the point cloud allows to map sub-vertical walls in their entirety in much shorter times than traditional surveying.</p><p>At this regard, two rock slopes were detected in the Sorrento Peninsula (Campania, southern Italy) with techniques that include traditional mapping, dictated by the guidelines of the International Society for Rock Mechanics, and the remote survey, through laser scanning and drone photogrammetry. The data obtained were processed automatically and manually through the Dips, CloudCompare and Discontinuity Set Extractor softwares.</p><p>In the present contribution we highlight the limits and advantages of the main data collection and the processing techniques, and provide an evaluation of the software packages currently available for the analysis and evaluation of discontinuities, in order to obtain a better characterization of the rock mass.</p>

Solution of Microseismic Monitoring Non-Linear Location Equations Based Matlab

2011 ◽  
Vol 94-96 ◽  
pp. 1628-1632
Author(s):  
Hong Shi ◽  
Lai Xue Pang ◽  
Rui Ying Shi
Keyword(s):  
Rock Mass ◽  
Iterative Method ◽  
Energy Release ◽  
Microseismic Monitoring ◽  
Newton Iterative Method ◽  
Monitoring Applications ◽  
Non Linear ◽  
The Future ◽  
Close Relationship ◽  
The Stability

Microseismic will produce when rock mass break. The occurrence of microseismic monitoring has close relationship to the energy release and crack's evolution in the rock mass. Therefore the microseismic monitoring can be used to predict the future rupture of the rock mass. MS location is the base of this prediction. The method of solving locating equation and the stability of answer are the key matter of microseismic monitoring applications in engineering fields. This paper uses Gauss-Newton iterative method to solve locating equation in order to advancing the precision and stability of answer and reducing the calculation workload. Based on the optimization toolbox of Matlab, the non-linear locating equations are solved and the visible locating results of microseismic are achieved.

Microseismic Monitoring of Hydraulic Fracturing – Data Interpretation Methodology with an Example from Pomerania

2017 ◽  
Author(s):  
Michał Antoszkiewicz ◽  
Mateusz Kmieć ◽  
Paweł Szewczuk ◽  
Marek Szkodo ◽  
Robert Jankowski
Keyword(s):  
Hydraulic Fracturing ◽  
Signal To Noise Ratio ◽  
Velocity Model ◽  
Data Interpretation ◽  
Microseismic Monitoring ◽  
Grid Search ◽  
Moment Tensors ◽  
Spatial Image ◽  
Microseismic Events ◽  
Breakage Mechanism

Microseismic monitoring is a method for localizing fractures induced by hydraulic fracturing in search for shale gas. The aim of this paper is to conduct the data interpretation of the microseismic monitoring based on the results from Pom-erania region of Poland. The data has been collected from an array of geophones deployed on the surface. Ground vibrations have been recorded and analyzed for fracture location, magnitude and breakage mechanism. A velocity model of underlying formations has been used for successful microseismic monitoring. The model has been further tuned with signal from perfora-tion shots of known location. Imaging of events has been done using software MicSeis, which utilizes diffraction stacking of waveforms from multiple stations to image microseismic events with low signal-to-noise ratio. The imaging of microseismic events in MicSeis uses a grid search over all possible origin times and locations in the selected rock volume. The seismic moment tensors are automatically determined from the amplitudes from the grid search procedure and are used to model po-larities of events which then enhance constructive interference. Function characterizing a maximum stack per time sample have been calculated over whole volume and analyzed using the STA/LTA algorithm. Once the event has been detected in time, location has been determined through analysis of the 3D spatial image function. The procedure has been used to detect five events during hydraulic fracturing in Pomerania.

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