Acoustic and elastic characterization of marine sediments by analysis, modeling, and inversion of ultrasonic P wave transmission seismograms

Ultrasonic P wave transmission seismograms recorded on sediment cores have been analyzed to study the acoustic and estimate the elastic properties of marine sediments from different provinces dominated by terrigenous, calcare ous, and diatomaceous sedimentation. Instantaneous frequencies computed fro m the transmission seismograms are displayed as gray-shaded images to give an acoustic overview of the lithology of each core. Centimeter-scale variat ions in the ultrasonic waveforms associated with lithological changes are i llustrated by wiggle traces in detail. Cross-correlation, multiple-filter, and spectral ratio techniques are applied to derive P wave velocities and a ttenuation coefficients. S wave velocities and attenuation coefficients, el astic moduli, and permeabilities are calculated by an inversion scheme base d on the Biot-Stoll viscoelastic model. Together with porosity measurements , P and S wave scatter diagrams are constructed to characterize different s ediment types by their velocity- and attenuation-porosity relationships. Th ey demonstrate that terrigenous, calcareous, and diatomaceous sediments cov er different velocity- and attenuation-porosity ranges. In terrigenous sedi ments, P wave velocities and attenuation coefficients decrease rapidly with increasing porosity, whereas S wave velocities and shear moduli are very l ow. Calcareous sediments behave similarly at relatively higher porosities. Foraminifera skeletons in compositions of terrigenous mud and calcareous oo ze cause a stiffening of the frame accompanied by higher shear moduli, P wa ve velocities, and attenuation coefficients. In diatomaceous ooze the contr ibution of the shear modulus becomes increasingly important and is controll ed by the opal content, whereas attenuation is very low. This leads to the opportunity to predict the opal content from nondestructive P wave velocity measurements at centimeter-scale resolution.