Relating seismic velocities, thermal cracking and permeability in Mt. Etna and Iceland basalts

Relating seismic velocities, thermal cracking and permeability in Mt. Etna and Iceland basalts We report simultaneous laboratory measurements of seismic velocities and fluid permeability on lava flow basalt from Etna (Italy) and columnar basalt from Seljadur (Iceland). Measurements were made in a servo-controlled steady-state-flow permeameter at effective pressures from 5–80 MPa, during both increasing and decreasing pressure cycles. Selected samples were thermally stressed at temperatures up to 900 °C to induce thermal crack damage. Acoustic emission output was recorded throughout each thermal stressing experiment. At low pressure (0–10 MPa), the P-wave velocity of the columnar Seljadur basalt was 5.4 km/s, while for the Etnean lava flow basalt it was only 3.0–3.5 km/s. On increasing the pressure to 80 MPa, the velocity of Etnean basalt increased by 45%–60%, whereas that of Seljadur basalt increased by less than 2%. Furthermore, the velocity of Seljadur basalt thermally stressed to 900 °C fell by about 2.0 km/s, whereas the decrease for Etnean basalt was negligible. A similar pattern was observed in the permeability data. Permeability of Etnean basalt fell from about 7.5×10 −16 m 2 to about 1.5×10 −16 m 2 over the pressure range 5–80 MPa, while that for Seljadur basalt varied little from its initial low value of 9×10 −21 m 2 . Again, thermal stressing significantly increased the permeability of Seljadur basalt, whilst having a negligible effect on the Etnean basalt. These results clearly indicate that the Etnean basalt contains a much higher level of crack damage than the Seljadur basalt, and hence can explain the low velocities (3–4 km/s) generally inferred from seismic tomography for the Mt. Etna volcanic edifice. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Rock Mechanics and Mining Sciences Elsevier

Relating seismic velocities, thermal cracking and permeability in Mt. Etna and Iceland basalts

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Publisher
Elsevier
Copyright
Copyright © 2005 Elsevier Ltd
ISSN
1365-1609
eISSN
1873-4545
D.O.I.
10.1016/j.ijrmms.2005.05.022
Publisher site
See Article on Publisher Site

Abstract

We report simultaneous laboratory measurements of seismic velocities and fluid permeability on lava flow basalt from Etna (Italy) and columnar basalt from Seljadur (Iceland). Measurements were made in a servo-controlled steady-state-flow permeameter at effective pressures from 5–80 MPa, during both increasing and decreasing pressure cycles. Selected samples were thermally stressed at temperatures up to 900 °C to induce thermal crack damage. Acoustic emission output was recorded throughout each thermal stressing experiment. At low pressure (0–10 MPa), the P-wave velocity of the columnar Seljadur basalt was 5.4 km/s, while for the Etnean lava flow basalt it was only 3.0–3.5 km/s. On increasing the pressure to 80 MPa, the velocity of Etnean basalt increased by 45%–60%, whereas that of Seljadur basalt increased by less than 2%. Furthermore, the velocity of Seljadur basalt thermally stressed to 900 °C fell by about 2.0 km/s, whereas the decrease for Etnean basalt was negligible. A similar pattern was observed in the permeability data. Permeability of Etnean basalt fell from about 7.5×10 −16 m 2 to about 1.5×10 −16 m 2 over the pressure range 5–80 MPa, while that for Seljadur basalt varied little from its initial low value of 9×10 −21 m 2 . Again, thermal stressing significantly increased the permeability of Seljadur basalt, whilst having a negligible effect on the Etnean basalt. These results clearly indicate that the Etnean basalt contains a much higher level of crack damage than the Seljadur basalt, and hence can explain the low velocities (3–4 km/s) generally inferred from seismic tomography for the Mt. Etna volcanic edifice.

Journal

International Journal of Rock Mechanics and Mining SciencesElsevier

Published: Oct 1, 2005

References

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