Use of Correlation Fractal Dimension signatures for understanding the Overlying Strata Dynamics in Longwall Coal Mines (original) (raw)
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Application of Correlation Integral and Fractal Dimension in Longwall Mine Safety
Longwall mining is considered as the most sophisticated form of coal mining and has very recovery. It is seen that in this form of mining the stress level in the roof strata plays a very important role in smooth running of the mines. The presence of stable roof strata over the coal seams sometimes creates problem in caving and the hanging load behind the face induces enormous amount on the powered supports. After reaching a critical limit the stress in the hanging strata is released in form of rock burst resulting in the total failure of the powered supports. Also the giant wind blowouts created results in fatalities in the mine. This paper attempts to describe the theory of using Fractal Dimension from Correlation Integral for locating the clustering of microseismic events in the roof strata that can be used for stress monitoring. It is seen that Fractal Dimension has been very helpful in locating stresses zones.
Engineering Geology, 2019
Mining of coal has always been a very risky task from older times and, is often associated with various fatal accidents in form of rock bursts, gas outbursts, slope/bench failure. Studies carried out by various safety agencies around the world such as MSHA (USA), DGMS (India), State Administration (China), have reported higher fatality rates in underground mines, and are mostly resulting from the sudden roof falls. Most of the roof falls occur suddenly in the running mine due to support failure or adverse strata conditions. The present study focuses on the monitoring of the roof falls in the longwall mine of Central India, as the presence of stable roof has resulted in several roof fall related accidents in various Indian longwall panels including Churcha mine, Kothadi mine and GDK-11A incline. The aforesaid accidents was also responsible for the poor performance of longwall mines in India, which is considered to be one of the best mining practices in majority of the coal producing countries of the world. The paper incorporates the spatial distribution and magnitude of microseismic events released before/during the roof falls and surface blasting in terms of Fractal Dimension as well as b-value. These two parameters helped in getting precursory signatures for spatio-temporal forecasting of minor and major roof falls, as well as helped in monitoring strata behavior during surface blasting. A total of sixty-four minor falls (LF1-LF64), seventy-six major falls (RF1-RF76) and fifteen surface blasting (SB1-SB15). The results showed decreasing trend in the both Fractal Dimension (D) and b-value before roof fall, as microseismic events emitted were highly clustered and had higher magnitude. Whereas, higher Fractal Dimension (D) and lower b-value was seen during surface blasting, when the emitted microseismic events had higher magnitude but were found to be dispersive in nature.
2019
Seismic hazards have become one of the common risks in underground coal mining and their assessment is an important component of the safety management. In this study, a methodology, involving nine fractal dimension-based indices and a fuzzy comprehensive evaluation model, has been developed based on the processed real time microseismic data from an underground coal mine, which allows for a better and quantitative evaluation of the likelihood for the seismic hazards. In the fuzzy model, the membership function was built using a Gaussian shape and the weight of each index was determined using the performance metric F score derived from the confusion matrix. The assessment results were initially characterised as a probability belonging to each of four risk levels (none, weak, moderate and strong). The comprehensive result was then evaluated by integrating the maximum membership degree principle (MMDP) and the variable fuzzy pattern recognition (VFPR). The model parameters of this methodology were first calibrated using historical microseismic data over a period of seven months at Coal Mine Velenje in Slovenia, and then applied to analyse more recent microseismic monitoring data. The results indicate that the calibrated model was able to assess seismic hazards in the mine.
Pure and Applied Geophysics, 2005
Several destructive earthquakes have occurred in the Kachchh region of Gujarat during the past two centuries, among them Allah Bund earthquake (M7.8) in 1819, Anjar earthquake (M6) in 1956 and the recent Bhuj earthquake (M7.6) in 2001. The Anjar earthquake was on KMF (Kachchh Mainland Fault) and the recent Bhuj events were caused by a hidden fault north of KMF. The present study discusses the fractal analysis of tectonics governing seismic activity in the region. The region has been divided into five blocks and the fractal dimension of each block has been calculated using the box-counting technique. The results show significantly low value of fractal dimension of the Kachchh rift block consisting of the KMF compared to the other surrounding blocks, which also contain faults and rifts of higher fractal dimension. This indicates that the cause of earthquakes in this block may be asperities and barriers. However, the predominance of aftershocks over foreshocks signifies that barriers may be the main cause. The other results, such as the lower value of dimension of fault clustering show that the Kachchh rift block has faults which are distributed in a clustered manner. In this context, the seismicity of this block seems to be high.
Fractal Dimension of the 1999 Chamoli Earthquake from Aftershock Studies in Garhwal Himalaya
Pure and Applied Geophysics, 2003
The Aftershock sequence of Chamoli earthquake (M w 6.4) of 29 March 1999 is analyzed to study the fractal structure in space, time and magnitude distribution. The b value is found to be 0.63 less than which is usually observed worldwide and in the Himalayas. This indicates that the numbers of smaller earthquakes are relatively less than the larger ones. The spatial correlation is 1.64, indicating that events are approaching a two-dimensional region meaning that the aftershocks are uniformly distributed along the trend of the aftershock zone. Temporal correlation is 0.86 for aftershocks of M ‡ 1, indicating a nearly continuous aftershock activity. However, it is 0.5 for aftershocks of M ‡ 1.75, indicating a non continuous aftershock activity. From the assessment of slip on different faults it is inferred that 70% displacement is accommodated on the primary fault and the remainder on secondary faults.
Fractal analysis of shallow and intermediate-depth seismicity of Hindu Kush
Chaos, Solitons & Fractals, 2019
Statistical seismology helps in understanding the underlying seismicity properties using some wellknown scaling relations that characterize different aspects of earthquake distribution. Among these scaling relations the Hurst (H) exponent has been extensively used to demonstrate the fractal properties of earthquake activity. In this study, we investigate the long-range correlations of seismicity parameters of shallow and intermediate-depth earthquakes of the Hindu Kush region using H statistics. The H index is computed for time window of 200 events with a slide of 15 data points on a complete and de-clustered catalog (1960-2007) prepared by Rehman et al. (2017). The long-range characteristics of seismicity are explored using size, time, space, depth and energy release. For shallow seismicity, the persistency (0.5 ≤ H ≤ 1) is found to be dominant except in a few periods of random walk. Contrary to this, intermediate-depth events show an evident change in H index around the time of major seismic events. Furthermore, the comparison of fractal behaviour of shallow and intermediate-depth seismicity confirms a notable difference in statistical properties. Our results also serve as a baseline study for seismicity analysis using multi-fractal approach for this region.
Annals of Geophysics, 2019
New Zealand earthquake that occurred on 15 th July 2009 (Mw 7.8) was analysed using fractal correlation dimension (Dc) and seismic b-value. We have analysed the earthquakes catalog of thirty-five years with a magnitude (mb ≥3.7), in order to observe a crucial information in terms of Dc value fluctuation for the event. The event is preceded by fall and anomalous change in Dc value in the year 2007 about two years prior to the mainshock. A sudden decrease in Dc value with highly clustered events is observed before the mainshock. The low value of Dc is an indicator of clustering and it shows how intermediate size events correlate with one another in the preparation process of this event. Here the low Dc value may be the indicator for high stress developer along the fault to produce large size earthquake. Moreover, we also observed abnormal fluctuation in b-value from 2003. The fractal clustering and scaling of earthquakes are indicated by b-value change prior to strong earthquake as a harbinger of stress correlation in various scales. The event is also marked for that occurred in the periphery of the positive Coulomb stress development, as obtained from three low Dc time windows' events. The drop in Dc value is not a single observation prior to this large event, but such pattern is also seen for other strong events in the study zone. One such well identified strong event is Mw 7.2 (2003) along with low Dc value prior to the event. Thus, stress correlation measured along with these indirect statistical tools gives the clue of selforganization of long wavelength of stress, which was not measured earlier with classical approaches. This type of study may provide a very useful information for hazard mitigation.
Fractal analysis of aftershock sequence of the Bhuj earthquake: A wavelet-based approach
2005
Wavelet-based fractal analysis of the aftershock data of the disastrous Bhuj earthquake (26 January 2001) has been carried out to understand the behaviour of the aftershocks. The Omori's curve suggests that the decay of aftershocks follows a power law relation with time. The p-value, known as 'decay constant' is found to be 0.88. The b-value of the region as obtained by wavelet variance analysis is close to 1, which is in agreement with the normal value for tectonically active regions. The results obtained from the multi-scale analysis of the aftershock sequence using the wavelets indicate that the fractal behaviour of aftershock data sustains up to certain scales only. Using the wavelet variance, the fractal dimension of the source is obtained as 2.06, which indicates that it is a 2D plane that is being filled up by the source fractures. The slip ratio that determines the fraction of total slip occurring on the primary fault is computed to be 0.48, which reveals that 48% of the total slip has occurred on the primary fault.