To understand the structure, composition and geological evolution of the Earth’s crust, one needs to know the seismic velocities of crustal rocks as a function of depth. An instrument capable of measuring simultaneously longitudinal (Vp) and shear (Vs) wave velocities in rock samples (25-45 mm diameter, 20-70 mm length) under uniaxial pressure (0-300 MPa) was designed and built. The measured velocities Vp (5520±130) m/s and Vs (3270±60) m/s under 300 MPa pressure for six dry mica schist samples from the Outokumpu Deep Drill Core were comparable to the literature values for samples from the same core hole, depth and mineralogy, measured under triaxial pressure. Hundred-and-five water saturated samples from depths of (125-1705) m measured under 30 MPa uniaxial pressure were compared with literature values of dry samples from the same bore hole, from depths (578-1845) m under (25-35) MPa triaxial pressure showing comparable results for Vs and 10% higher values for Vp, as expected because of water saturation effect. This can be also explained by different sample lithologies. The main contribution of this thesis is to provide a means to measure Vp and Vs of samples from the Outokumpu Deep Drill Core under crustal conditions using uniaxial pressure without the need to shape the sample geometry. The device provides also a way to calculate Vp/Vs-ratios and simultaneously Poisson ratios, seismic impedances and reflection coefficients for various lithological pairs thus enhancing seismic interpretations.
|Tila||Julkaistu - 2009|