High Vp/Vs ratio: Saturated cracks or anisotropy effects?

摘要: [1] We measured Vp/Vs ratios of thermally cracked Westerly granite, Carrara marble and 4% porosity Fontainebleau sandstone, for an effective mean pressure ranging from 2 to 95 MPa. Samples were fluidsaturated alternatively with argon gas water (5 MPa constant pore pressure). The experimental results show that at ultrasonic frequencies, ratio saturated specimen never exceeded 2.15, even as low MPa, or a lithology which the Poisson’s minerals is high 0.3 (calcite). In order check these against theoretical models: we examine first randomly oriented medium (with dispersion but without anisotropy); second horizontally aligned cracks anisotropy dispersion). numerical data agree well model: frequency, range 1.6 1.8 in dry case 2.2 case. model predicts both Vp/Sv Vp/Sh vary 1.2 3.5, depending on raypath angle relative crack fabric. addition, perpendicular fabric, predicted absence shear wave splitting. From results, argue possibility (>2.2) recently imaged by seismic tomography subduction zones, may come zones presenting important anisotropy. cumulative effects fluid are required get above 2.2. Citation: Wang, X.-Q., A. Schubnel, J. Fortin, E. C. David, Y. Gueguen, H.-K. Ge (2012), High ratio: Saturated effects?, Geophys. Res. Lett., 39, L11307, doi:10.1029/2012GL051742.