Fracture process zone in granite: a microstructural analysis

Janssen, Ch.; Wagner, F.; Zang, Arno; Dresen, Georg

doi:10.1007/s005310000157

Cited by 70 publications

(32 citation statements)

References 17 publications

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“…1c) with crack damage increasing strongly towards the fault (Zang et al, 2000). However, the width of the process zone in cross section as defined by the distribution of AEs or microcracks depends on the resolution of the method and may vary considerably (Janssen et al, 2001).…”

Section: Monitoring the Failure Process: Acoustic Emission Activity Amentioning

confidence: 99%

Passive Seismic Monitoring of Natural and Induced Earthquakes: Case Studies, Future Directions and Socio-Economic Relevance

Bohnhoff

Dresen

Ellsworth

et al. 2009

New Frontiers in Integrated Solid Earth Sciences

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An important discovery in crustal mechanics has been that the Earth's crust is commonly stressed close to failure, even in tectonically quiet areas. As a result, small natural or man-made perturbations to the local stress field may trigger earthquakes. To understand these processes, Passive Seismic Monitoring (PSM) with seismometer arrays is a widely used technique that has been successfully applied to study seismicity at different magnitude levels ranging from acoustic emissions generated in the laboratory under controlled conditions, to seismicity induced by hydraulic stimulations in geological reservoirs, and up to great earthquakes occurring along plate boundaries. In all these environments the appropriate deployment of seismic sensors, i.e., directly on the rock sample, at the earth's surface or in boreholes close to the seismic sources allows for the detection and location of brittle failure processes at sufficiently low magnitudedetection threshold and with adequate spatial resolution for further analysis. One principal aim is to develop an improved understanding of the physical processes occurring at the seismic source and their relationship to the host geologic environment. In this paper we review selected case studies and future directions of PSM efforts across a wide range of scales and environments. These include induced failure within small rock samples, hydrocarbon reservoirs, and natural seismicity at convergent and transform plate boundaries. Each example represents a milestone with regard to bridging the gap between laboratory-scale experi-M. Bohnhoff ( ) Department of Geophysics, Stanford University, Stanford, CA 94305-2215, USA e-mail: marcob@stanford.edu ments under controlled boundary conditions and largescale field studies. The common motivation for all studies is to refine the understanding of how earthquakes nucleate, how they proceed and how they interact in space and time. This is of special relevance at the larger end of the magnitude scale, i.e., for large devastating earthquakes due to their severe socio-economic impact.

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Section: Monitoring the Failure Process: Acoustic Emission Activity Amentioning

confidence: 99%

Passive Seismic Monitoring of Natural and Induced Earthquakes: Case Studies, Future Directions and Socio-Economic Relevance

Bohnhoff

Dresen

Ellsworth

et al. 2009

New Frontiers in Integrated Solid Earth Sciences

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“…1). Microstructure analysis of undeformed Aue granite yielded crack densities in the range of 0.3-0.6 mm )1 (JANSSEN et al, 2001). No data exist for the Etna basalt, however, the block from which samples were cored contains abundant mm-to cmscale cracks that possibly result from rapid cooling (VINCIGUERRA et al, 2005).…”

Section: Sample Materials and Testing Proceduresmentioning

confidence: 99%

Ultrasonic Velocities, Acoustic Emission Characteristics and Crack Damage of Basalt and Granite

Stanchits

Vinciguerra

Dresen

2006

Pure appl. geophys.

248

184

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Acoustic emissions (AE), compressional (P), shear (S) wave velocities, and volumetric strain of Etna basalt and Aue granite were measured simultaneously during triaxial compression tests. Deformation-induced AE activity and velocity changes were monitored using twelve P-wave sensors and eight orthogonally polarized S-wave piezoelectric sensors; volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the rock surface. P-wave velocity in basalt is about 3 km/s at atmospheric pressure, but increases by > 50% when the hydrostatic pressure is increased to 120 MPa. In granite samples initial P-wave velocity is 5 km/s and increases with pressure by < 20%. The pressure-induced changes of elastic wave speed indicate dominantly compliant low-aspect ratio pores in both materials, in addition Etna basalt also contains high-aspect ratio voids. In triaxial loading, stress-induced anisotropy of Pwave velocities was significantly higher for basalt than for granite, with vertical velocity components being faster than horizontal velocities. However, with increasing axial load, horizontal velocities show a small increase for basalt but a significant decrease for granite. Using first motion polarity we determined AE source types generated during triaxial loading of the samples. With increasing differential stress AE activity in granite and basalt increased with a significant contribution of tensile events. Close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly. A concomitant increase of doublecouple events indicating shear, suggests shear cracks linking previously formed tensile cracks.

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“…Lockner, 1995;Zang et al, 2000) and afterwards compared with the microstructure of the deformed sample (e.g. Swanson, 1987;Janssen et al, 2001).…”

Section: Process Zone and Damage Zone In Rock Deformationmentioning

confidence: 99%

Magma-driven hydraulic fracturing and infiltration of fluids into the damaged host rock, an example from Dronning Maud Land, Antarctica

Engvik

Bertram

Kalthoff

et al. 2005

Journal of Structural Geology

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Excellent outcrops in Dronning Maud Land, Antarctica, provide unique insight into the mode and extent of fluid infiltration into metamorphic and plutonic rocks in the middle crust. The fluids are liberated from pegmatitic veins and give rise to alteration halos. In the alteration halos, the conspicuous change in colour is correlated with (1) hydration mineral reactions, and (2) high density of microcracks in quartz and feldspar exceeding that observed in the unaltered host rock by an order of magnitude. The field relations indicate that the veins originated as melt-driven hydraulic fractures, sealed by pegmatite and aplite crystallising from volatile-rich melts, with the alteration halo being the wake of the process zone formed at the tip of the propagating fractures. It is proposed that (1) the size of the alteration zone and the width of the vein are correlated, resulting in higher values of both these quantities for cracks propagating at higher velocities and consequently higher crack propagation toughnesses; (2) the damage zone is characterised by a transient state of high permeability which was short-lived due to rapid healing and sealing of microcracks; (3) the infiltration and retrogression of the high-grade rocks can be considered as a quasi-instantaneous process on geologic time scales with a duration of hours to weeks. q

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Fracture process zone in granite: a microstructural analysis

Cited by 70 publications

References 17 publications

Passive Seismic Monitoring of Natural and Induced Earthquakes: Case Studies, Future Directions and Socio-Economic Relevance

Passive Seismic Monitoring of Natural and Induced Earthquakes: Case Studies, Future Directions and Socio-Economic Relevance

Ultrasonic Velocities, Acoustic Emission Characteristics and Crack Damage of Basalt and Granite

Magma-driven hydraulic fracturing and infiltration of fluids into the damaged host rock, an example from Dronning Maud Land, Antarctica

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