Publication Date:
2017-04-04
Description:
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.
Description:
Published
Description:
974-993
Description:
reserved
Keywords:
Acoustic emission
;
ultrasonic velocity
;
fracture
;
rock
;
04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism
;
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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