期刊
INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES
卷 42, 期 7-8, 页码 900-910出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijrmms.2005.05.022
关键词
physical properties; lava flows; columnar basalts; thermal cracking
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 degrees 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 degrees 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 x 10(-16) m(2) to about 1.5 x 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 X 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. (c) 2005 Elsevier Ltd. All rights reserved.
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