日本地球惑星科学連合2019年大会

講演情報

[E] 口頭発表

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT24] Attenuation from crust to core: in situ experiments, observaions and implications

2019年5月26日(日) 09:00 〜 10:30 A09 (東京ベイ幕張ホール)

コンビーナ:小西 健介(台湾中央研究院地球科学研究所)、片山 郁夫(広島大学大学院理学研究科地球惑星システム学専攻)、芳野 極(岡山大学惑星物質研究所)、Alexandre Schubnel(CNRS)、座長:Kensuke Konishi(Institute of Earth Sciences)

09:45 〜 10:00

[SIT24-04] Frequency effects on elastic properties of saturated porous rocks: Experimental investigations

★Invited Papers

*Jerome Fortin1 (1.Laboratoire de Géologie, Ecole Normale Superieure - Paris)

キーワード:porous rock, velocity dispersion, squirt-flow

Comparing ultrasonic measurements (1 MHz) in the laboratory and seismic (100 Hz) or logging (10 kHz) measurements at the field scale is not straightforward due to the dispersion of body-wave velocities. In rocks fully saturated by a Newtonian fluid, dispersion is related to fluid flow at different scales, separating three regimes: the drained, undrained, and unrelaxed regimes.

In this work, the elastic dispersion and attenuation of different sedimentary rocks have been measured over a large frequency range. To cover the frequency range, forced oscillations (0.004 to 100 Hz) and ultrasonic (1 MHz) measurement techniques were done in a triaxial cell, at various differential pressures, on samples saturated by fluids of very different viscosity. The forced oscillations include both hydrostatic and axial oscillations to deduce the bulk and Young moduli, respectively.

For all the samples, we observe the drained–undrained transition and its consequence on the attenuation and the elastic moduli dispersion. Biot-Gassmann’s theory is found to be valid to explained the increased of the elastic moduli from the drained to the undrained regime. Some samples exhibit a second transition from the undrained to the unrelaxed regime, and is explained a squirt-flow mechanism. For this second transition, the rock microstructure, especially the crack density and the crack aspect ratio seems to be the major contributor of the magnitude of the dispersion and attenuation.