Lithological Controls on Seismicity in Granitic Rocks

Collins, D. M.; Young, R. P.

doi:10.1785/0119990142

Cited by 42 publications

(24 citation statements)

References 27 publications

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“…Finally, we would like to point out that both in limestones and sandstones, depressurization induces large decreases of elastic wave velocities (dashed lines on Figure 13), which proves the important role played by stress relief cracking in crack propagation. Such an observation was also performed on very low porosity calcic rocks such as Carrara marble and Solnhoffen limestone [ Schubnel et al , 2005] and even granites from the URL underground laboratory [ Collins and Young , 2000]. This points out as well the limitations of postmortem microstructural investigations.…”

Section: Interpretationsmentioning

confidence: 99%

Effects of pore collapse and grain crushing on ultrasonic velocities and V_p/V_s

2007

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[1] Compressional, shear wave velocities and their ratio, V p /V s , were measured along with porosity variations during wet and dry hydrostatic compaction of Bleurswiller sandstone, a 25% porosity Vosgian sandstone. At first, increase in hydrostatic pressure was accompanied by a simultaneous increase of both V p and V s as expected. At a critical effective confining pressure P*, a large mechanical decrease of porosity was observed that was due to pore collapse and grain crushing. Theoretically, two different processes are affecting the elastic wave velocities in counteracting ways during cataclastic compaction: cracking and porosity decrease. Our experimental results show that cracking is the dominant effect, so that grain crushing and porosity reduction were accompanied by a large decrease in velocities. The ratio V p /V s was also observed to change during our experiments: In the wet specimen, V p /V s value increased from 1.72 to 1.84, while in the dry specimen, it increased from 1.59 below P* to 1.67 beyond P*, respectively. To quantitatively interpret these results, an isotropic effective medium model (EM) was used that considered the sandstone as a mixture of spheroidal pores and penny-shaped cracks. In particular, the increase in V p /V s , in the wet case, is well reproduced and shows the important role played by the mechanical coupling of fluid with low aspect ratio cracks (<10 À2 ). In the dry case, however, our experimental results highlight an increase of V p /V s ratio during cataclastic compaction, in apparent contradiction with the predictions of the EM model. Indeed, increases in V p /V s ratio, and hence in Poisson's ratio, are, in general, attributed to fluid saturation. A closer look to the microstructure may provide a possible interpretation: Beyond P*, grains are no longer cemented. Using Digby's granular model as an alternative model, we were able to reach a quantitative agreement with the experimental results. The possible implication is that in both dry and wet conditions, cataclastic compaction due to grain crushing induces an increase in V p /V s ratio.Citation: Fortin, J., Y. Guéguen, and A. Schubnel (2007), Effects of pore collapse and grain crushing on ultrasonic velocities and V p /V s ,

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Section: Interpretationsmentioning

confidence: 99%

Effects of pore collapse and grain crushing on ultrasonic velocities and V_p/V_s

2007

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“…In the field, the implementation of high‐frequency accelerometers monitoring smaller volumes of rock has led to an increased magnitude resolution when monitoring mining and fluid‐induced seismicity. At the Underground Research Laboratory (URL) in Manitoba, Canada, Gibowicz et al [] and Collins and Young [] were able to record and analyze seismic data in the magnitude range −4.2 < M w <−2. Source parameters showed a relatively constant stress drop‐scaling relationship with static stress drops (Δ σ ) ranging from 0.1 to 3 MPa.…”

Section: Introductionmentioning

confidence: 99%

A laboratory acoustic emission experiment under in situ conditions

Goodfellow

Young

2014

Geophysical Research Letters

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In this paper, we revisit acoustic emission (AE) data from an in situ rock fracture experiment conducted at the Underground Research Laboratory (URL) in Manitoba, Canada. The Mine‐By experiment, a large‐scale excavation response test, was undertaken at a depth of 420 m and involved the mechanical excavation of a cylindrical tunnel. During the experiment a small array of 16 Panametrics V103 AE sensors enclosed a 0.7 m × 0.7 m × 1.1 m rectangular prism of Lac du Bonnet granite located in the tunnel wall. The V103 sensors were later calibrated in the laboratory, and a source parameter analysis was undertaken using a spectral fitting method. Corner frequency and moment magnitude were found to be inside the ranges 250 kHz

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“…Example waveforms recorded from the MS system are displayed by COLLINS and YOUNG (2000). AE and MS source locations were calculated by a Simplex/Geiger method (ESG, 2000) using P-wave arrival times, a homogeneous velocity model, and assuming straight ray paths.…”

Section: Seismic Processing Methodologymentioning

confidence: 99%

High-resolution Mechanics of a Microearthquake Sequence

Collins¹,

Pettitt²,

Young³

2002

Pure appl. geophys.

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Ð Unique data from microseismic (MS) and acoustic emission (AE) systems monitoring a common rock volume have been analyzed from the Underground Research Laboratory in Canada. The two 16 sensor systems were installed to investigate stress-induced microcracking around clay and concrete bulkheads as part of the Tunnel Sealing Experiment. Single and double MS events are found to be spatially associated with clusters of between 19±86 higher frequency AE events. Each AE cluster is elongated with the longest axis between 15 and 50 cm. The AE events occurring before the associated MS event are termed foreshocks, and for two of the three analyzed AE clusters an acceleration in the AE frequency and cumulative magnitude occurs upto the time of the MS event, however with one AE cluster very few foreshocks are recorded, possibly indicating a more homogeneous failure plane. Time independent moment tensors were determined with the MS events showing signi®cant deviatoric sources. The majority of the AE events have deviatoric mechanisms with a few crack opening and crack closure type events also determined. This study highlights the bene®ts of using small-scale seismic systems to investigate the temporal fracture mechanics of microcrack formation, and allows comparisons with larger more damaging seismicity.

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Lithological Controls on Seismicity in Granitic Rocks

Cited by 42 publications

References 27 publications

Effects of pore collapse and grain crushing on ultrasonic velocities and V_p/V_s

Effects of pore collapse and grain crushing on ultrasonic velocities and V_p/V_s

A laboratory acoustic emission experiment under in situ conditions

High-resolution Mechanics of a Microearthquake Sequence

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Lithological Controls on Seismicity in Granitic Rocks

Cited by 42 publications

References 27 publications

Effects of pore collapse and grain crushing on ultrasonic velocities and Vp/Vs

Effects of pore collapse and grain crushing on ultrasonic velocities and Vp/Vs

A laboratory acoustic emission experiment under in situ conditions

High-resolution Mechanics of a Microearthquake Sequence

Contact Info

Product

Resources

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Effects of pore collapse and grain crushing on ultrasonic velocities and V_p/V_s

Effects of pore collapse and grain crushing on ultrasonic velocities and V_p/V_s