Correlating Seismic Wave Velocities with the Physicomechanical Properties of Carbonate Rocks

Seismic wave velocities (both P and S waves) measurements have been carried out for carbonate rock samples collected from Lesser Himalayan deposits exposed along Alaknanda valley between Rudraprayag to Helang village in Uttarakhand, India. This study has been carried out to evaluate the effect of the petrophysical and the mechanical properties of rocks on seismic wave velocities. On the core samples, petrophysical and mechanical measurements were performed where porosity, density, water absorption, and seismic wave velocities were first determined, followed by measuring the uniaxial compressive strength (UCS), and Brazilian tensile strength (BTS). Thin sections were prepared to measure the petrographic parameters (textural properties and mineralogical composition). This study focuses mainly on grain size and mineral composition. Petrographic investigation and X-ray diffraction (XRD) analysis were done to identify their mineralogy. Both petrographic and XRD analysis revealed that the main constituting minerals are dolomite, and in minor amounts, calcite, quartz, and opaque minerals are present. Interrelationships between seismic wave velocities and porosity, density, mineral constituents, grain size, uniaxial compressive strength, and Brazilian tensile strength were obtained using regression analysis. It has been concluded that there are significant positive correlations between compressional wave velocity and uniaxial compressive strength (r² = 0.82), Brazilian tensile strength (r² = 0.67). Similarly, strong to moderate correlations were found between shear wave velocity and uniaxial compressive strength (r² = 0.73), Brazilian tensile strength (r² = 0.68). Weak to moderate negative correlations were found between seismic wave velocities and porosity. Moderate positive correlations have been found between seismic wave velocities and dry density. There is moderate negative correlation has been found between uniaxial compressive strength and grain size. Furthermore, it has also been concluded that the influence of grain size on rock strength was more important than mineral content.