Seismicity In Mines

Recent seismological research has focused on processes other than pure shear failure (double-couple) as an alternative mechanism for some types of seismic events. This has been stimulated by what appears to be anomalous focal mecha nisms observed for several earthquakes of possible volcanic nature in the 1980 Mammoth Lakes, California sequence (JULIAN and SIPKIN, 1985; SIPKIN, 1986). Although studies have concentrated on earthquakes associated with magmatic processes, possible non-double-couple seismic failure has been observed, but not widely known, in cases of mine seismicity in the past three decades. Such cases have occurred on a world-wide basis; however, no cases until now have been observed in the United States. The existence of non-double-couple failure in mine seismicity has been controversial as it has been for tectonic/volcanic earthquakes. Several of the benchmark studies of mine seismicity in the deep South African gold mines have resulted in the belief that no fundamental distinction in the source mechanism exists between tectonic earthquakes and rock bursts (MCGARR, 1984); both types of events are the result of pure shear failure. However, the reported cases of implo sional focal mechanisms for mine seismicity continue to increase in number and prolong the controversy. During the summer of 1984, a three-dimensional, high resolution micro earthquake network was operated by Woodward-Clyde Consultants (WCC) in the vicinity of two coal mines beneath Gentry Mountain in the eastern Wasatch Plateau of central Utah.

These proceedings include the latest developments in research and practice in the area of mining-induced seismicity. Three themes are explored: strong ground motion and rockburst hazard; mechanics of seismic events and stochastic methods; and monitoring of seismicity and geomechanical modelling.

Routine seismic monitoring in mines was introduced over 30 years ago with two main objectives in mind: • immediate location of larger seIsmIC events to guide rescue operations; • prediction of large rockmass instabilities. The first objective was achieved fairly quickly, but with the subsequent development of mine communication systems, its strategic importance has diminished. The very limited success with prediction can, at least partially, be attributed to three factors: • seismic monitoring systems based on analogue technology that provided noisy and, frequently, poorly calibrated data of limited dynamic range; • the non-quantitative description of a seismic event by at best its local magnitude; and • the resultant non-quantitative analysis of seismicity, frequently through parameters of some statistical distributions, with a somewhat loose but imaginative physical interpretation. The introduction of modern digital seismic systems to mines and progress in the theory and methods of quantitative seismology have enabled the implementation of realtime seismic monitoring as a management tool, quantifying rockmass response to mining and achieving the first tangible results with prediction. A seismic event, being a sudden inelastic deformation within the rockmass, can now routinely be quantified in terms of seismic moment, its tensor, and radiated seismic energy, so that the overall size of, and stress released at, the seismic source can be estimated.

The perturbation of the earth by mankind causes earthquakes in a variety of situations. This phenomenon continues to be a major concern to engineers and scientists concerned with the mitigation of the consequences of this seismicity, as well as better understanding the processes at its origin. The present volume contains twelve papers from six countries, dealing with observations of triggered and induced seismicity in four continents. The reported cases include seismicity due to hard-rock mines, coal mines, underground research facilities for nuclear waste disposal, water injections, reservoirs, acquifers and oil fields. This volume provides case studies of previously unavailable observations of this phenomenon, investigations of the cause and source mechanism of seismic events, studies of source location distributions, determinations of seismic source parameters, cases of the use of such parameters in assessing rockburst hazard in mines, and measurements of velocity an attenuation properties of rock masses. The present collection of papers provides an excellent indication of the current state of the art and new developments in this area of research.

An Introduction to Mining Seismology describes comprehensively the modern methods and techniques used to monitor and study seismicity and rockbursts in mines. Key case histories from various worldwide mining districts clearly illustrate and skillfully emphasize the practical aspects of mining seismology. This text is intended as a handbook for geophysicists and mining and rock mechanics engineers working at mines. It will also serve as an essential reference tool for seismologists working at research institutions on local seismicity not necessarily induced by mining. Presents a comprehensive description of seismicity induced by mining worldwide Provides information on optimum network planning and seismic event location procedures in deep mines Covers a broad array of topics including focal mechanism, moment tensor, and double-couple versus non-double-couple seismic events in mines Includes data on source parameters and scaling relations for seismic events in mines

This volume contains 18 papers from 8 countries dealing with different aspects of triggered and induced seismicity. In situ observations of the phenomenon include examples of seismicity due to reservoirs, hard-rock mines, coal mines, mine collapses, brine production caverns, fluid injections, and geothermal hot-dry-rock projects. High-frequency acoustic emission studies from laboratory experiments and hard-rock mines have also been reported. Besides providing case studies of previously unavailable observations of seismicity, the present volume contains investigations of the causes and source mechanism of seismic events, determination of source parameters, seismic hazard as related to the design of support systems for underground openings and procedures for closure of brine production caverns, and the use of seismic and non-destructive techniques in assessing rock damage, measuring dynamic elastic moduli and detecting discontinuities. This collection of papers provides an excellent indication of the state of the art, recent developments and outstanding challenges facing scientists and engineers in understanding the causes and alleviating the effects of induced seismicity.