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

S. Vinciguerra, C. Trovato, P. G. Meredith, Philip Benson

    Research output: Contribution to journalArticlepeer-review

    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 m2 to about 1.5×10−16 m2 over the pressure range 5–80 MPa, while that for Seljadur basalt varied little from its initial low value of 9×10−21 m2. 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.
    Original languageEnglish
    Pages (from-to)900-910
    Number of pages11
    JournalInternational Journal of Rock Mechanics and Mining Sciences
    Volume42
    Issue number7-8
    DOIs
    Publication statusPublished - 2005

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