6:15 PM - 7:30 PM
[SSS29-P16] Dependences of pore pressure on elastic wave velosities and Vp/Vs ratio for thermally cracked gabbro
Keywords:Gabbro, Vp/Vs ratio, Elastic wave velosity, High pore pressure
To prepare specimens with various fracture distribution, the rock specimens were heated at 500 ℃ and 700 ℃ for 24 hours. We also did measurement with an intact rock specimen. We measured Vp and Vs by using transmission method, with putting piezoelectric elements on the specimen. Before measuring Vp and Vs at confining and pore pressure, we did measurements under atmospheric pressure, and revealed the anisotropy of the velocities of up to 10 %. We measured Vp and Vs for four directions at confining and pore pressure. Confining pressure was constant, 50 MPa, and pore pressure was decreased from 49 to 0.1 MPa and then increased to 49 MPa. For the specimen thermally cracked under 500 ℃, when pore pressure was 49 MPa, Vp/Vs ratio was 2.0〜2.1. This is close to the value of Vp/Vs which was obtained by marine seismic refraction. On the other hand, the Vp/Vs ratio of intact rock did not change as pore pressure changed and were almost constant, approximately 1.5.
At the presentation, we will also show the results of measurements of fracture distribution such as fracture densities or apertures, and reveal the relationship between them and the results of the experiment.
This work was supported by JSPS KAKENHI Grant Number 26400492.