1、英文原文Triggering of Seismicity Remote from Active Mining ExcavationsBy S.D.McKinnonDepartment of Mining Engineering, Queens University, Kingston,Ontario, CanadaSummaryObservations of seismicity and ground control problems in the Sudbury mining camp have shown that late-stage (young) sub-vertical strik
2、e-slip faults are sensitive to small mining-induced stress changes. The strength-limited nature of stress measurements made in the region indicates that these structures are in a state of marginal stability. Numerical continuum models are developed to analyze the behavior of such structures. In the
3、models, shear strain localizations (faults) evolve such that there is close interaction between the fault system, stresses, and boundary deformation. Fault slip activity in these systems is naturally sporadic and reproduces the commonly observed Gutenberg-Richter magnitude frequency relation. It is
4、shown that a relatively minor disturbance to such a system can trigger significant seismicity remote from the source of the disturbance, a behavior which cannot be explained by conventional numerical stress analysis methodologies. The initially uniform orientation of the stress field in these system
5、s evolves with increasing disorder, which explains much of the scatter commonly observed in data sets of stress measurements. Based on these results, implications for stress measurement programs and numerical stability analysis of faults in mines are discussed.Keywords: Triggering, microseismicity,
6、stress analysis, rockbursts, fault stability.1 IntroductionThe majority of seismic events around deep hard rock mines occur close to excavation boundaries. These events are related to mining-induced stress changes leading to damage involving fracturing of intact rock or slip along pre-existing disco
7、ntinuities. Extraction layouts leading to highly stressed structures such as pillars and abutments are particularly prone to induced seismicity. With appropriate calibration of rock mass strength, numerical stress analysis can be used to estimate the extent of fracturing and therefore the extent of
8、near-excavation seismicity (Beck et al., 1997; Potvin and Hudyma, 2001; Beck and Brady, 2002). Characteristics of near-excavation seismicity include swarms of events triggered by production blasts (which cause a rapid change in the stress field), followed by a gradual decay in event frequency to bac
9、kground levels over a period of hours or days. The regularity in the frequency and location of near-excavation events makes this type of seismicity a manageable mining problem.A certain amount of seismicity also occurs further away from mining excavations and appears to be uncorrelated in time and s
10、pace with mining activities. Events have been recorded hundreds of meters away from active mining. On the basis of source locations, it has long been recognized that these events are the result of slip on preexisting structures such as faults, dykes or contacts (Smith et al., 1974; Gay et al., 1984)
11、. Although the number of events close to mining excavation boundaries vastly exceeds those further away, the latter are of great concern to mining since they tend to be of larger magnitude, increasing the risk of rockburst damage. Since neither their location nor magnitude can be predicted in advanc
12、e, mines must consequently make more extensive use of heavier ground support to control potential rockburst damage than would be required if events were only located close to active mining excavations.Due to the complex geometry and geological environment of most mines and the availability of numero
13、us commercially supported codes, numerical stress analysis is the tool of choice for the majority of mining stability analysis. However, only a limited amount of success has been obtained in using numerical modelling to understand seismic events on faults and other geological structures. In particul
14、ar, numerical stress analysis has not been able to explain the occurrence of seismic events remote from mining. Due to the widespread use of numerical stress analysis in the mining industry, it would be desirable to develop a methodology that would enable modelling to be used to explain both types o
15、f seismic events. The objective of this paper is to present an investigation into the cause of seismic events remote from mining and the implications for applying numerical stress analysis to the problem. As would be expected, this type of seismicity is strongly influenced by the geological environm
16、ent in which the mine is located. Motivation for the approach to modelling mining-remote seismicity is taken from stress measurements and known geological controls of seismicity in the Sudbury mining camp, which is a region of intensive mining activity in Ontario, Canada.2 Structural Geology and State of Stress in the Sudbury Structure2.1 Structural GeologyThe mines of the Sudbury camp are located in a unique and complex geological formation called the Sudbury Str
