EVALUATION AND PREDICTION OF SHEAR-WAVE VELOCITIES IN CALCAREOUS MARINE SEDIMENT AND ROCKS

Shear wave velocities from full waveform acoustic logs recorded in calcareous oozes and chalks were determined using the spectral ratio inversion method. Data were recorded during DSDP Leg 95 drilling off the east coast of the United States. DSDP Site 613 sampled a progression of carbonaceous-siliceous oozes through partially lithified chalk. Discrete shear wave velocities within a 350 meter interval were calculated. The results of a method for predicting shear wave velocities using Wood's equation correlate well with inversion results at shear wave velocities greater than 800 m/sec. Predictions using Wood's equation provide a theoretical maximum value for shear wave velocity to compare with inversion results. Inverted data fall just below the predicted theoretical maximum value from Wood's equation and agree quite well with trends in Wood's results and other related logging measurements. At slower shear wave velocities the physical contrast between borehole fluid (drilling mud) and the formation (ooze) is not enough to excite normal borehole modes used in inversion processing, resulting in inversion velocities greater than Wood's maximum.