Browsing by Author "Brown, Laura Grace"

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Quantification of seismic responses to mining using novel seismic response parameters
(2018-10-05) Brown, Laura Grace
Mining-induced seismic events can be loosely classified as induced events or triggered events. Induced seismic events in mines are typically proportional to mining-induced stress change. This type of rock mass failure is often successfully managed by seismically active underground mining operations, and is generally considered part of a normal seismic response to mining. Triggered seismicity represents a disproportional seismic response to mining, and often results in visible rock mass damage. The variations in space and time characteristics of induced and triggered seismicity, particularly in relation to mine blasting, are indicative of distinct seismic source mechanisms and may be useful in seismic hazard evaluation for mines. In this work, Seismic Response Parameters (SRP's) are conceptualized using fundamental rock mechanics and mine seismicity principles, and subsequently supported with a comprehensive case study from Agnico Eagle's LaRonde mine. The primary factors considered in this thesis are space and time; how they relate a seismic response to the stimulus and how they relate individual events within a seismic response to the response itself. The four SRP's are: Distance to Blast, Time After Blast, Distance to Centroid and Time Between Events. A normalized set of SRP's, calculated with site specific considerations, are proposed as a meaningful measure of how likely a seismic response is to be induced or triggered by discrete mine blasting. Within this thesis, Seismic Response Rating (SRR), the summation of normalized SRP's, is presented as a means of quantifying seismic responses to mining with a single numerical value. Seismic responses at LaRonde mine are used to demonstrate the application of SRP's and SRR to real mine seismic data. A mine shutdown period, in which no mine blasting occurs, is used to provide meaningful insight into the spatial and temporal relations of mine seismicity. In the absence of mine blasting, seismic events associated with induced seismic source mechanisms cease to obscure triggered seismicity (resulting from triggered source mechanisms). Where and when both induced and triggered seismic source mechanisms interact in space and time, complex seismicity may be observed. An interpretation of complex seismic responses to mining, occurring in the transitional zone between induced and triggered seismicity, is also presented in this thesis.
Seismic hazard evaluation using apparent stress ratio for mining-induced seismic events
(2015-08-20) Brown, Laura Grace
This thesis investigates precursory trends in seismic data prior to the occurrence of large and potentially damaging seismic events at Agnico Eagle’s LaRonde mine. A variety of sample populations are selected to represent varying degrees of seismic hazard within a large area of interest at LaRonde. The main factor considered for hazard assessment is the local stress conditions within the rock mass, inferred from the apparent stress of seismic events. An alternative means of analyzing apparent stress measurements using a relative ratio, referred to as Apparent Stress Ratio (ASR), is presented. The use of a ratio eliminates the need for thresholds values to define high and abnormal apparent stress. ASR values are analyzed in reference to varying time frames, allowing for changes in stress conditions over time to be considered. Hazard maps created using ASR and peak ASR values correspond well to areas of elevated seismic hazard previously identified at LaRonde. For an area of interest at LaRonde, ASR as an alarm tool possesses a success rate of 68% with a false alarm ratio of 2:1.