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Authors: Stanchits, S.* 
Vinciguerra, S.* 
Dresen, G.* 
Title: Ultrasonic velocities, acoustic emission characteristics and crack damage of basalt and granite
Journal: Pure and Applied Geophysics 
Series/Report no.: /163 (2006)
Publisher: Birkhauser
Issue Date: 2006
DOI: 10.1007/s00024-006-0059-5
Keywords: Acoustic emission
ultrasonic velocity
Subject Classification04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism 
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks 
Abstract: 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 initialP-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 determinedAE source types generated during triaxial loading of the samples. With increasing differential stressAEactivity 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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