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

Abstract

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, calcareous, and diatomaceous sedimentation. Instantaneous frequencies computed from the transmission seismograms are displayed as gray‐shaded images to give an acoustic overview of the lithology of each core. Centimeter‐scale variations in the ultrasonic waveforms associated with lithological changes are illustrated by wiggle traces in detail. Cross‐correlation, multiple‐filter, and spectral ratio techniques are applied to derive P wave velocities and attenuation coefficients. S wave velocities and attenuation coefficients, elastic moduli, and permeabilities are calculated by an inversion scheme based on the Biot‐Stoll viscoelastic model. Together with porosity measurements, P and S wave scatter diagrams are constructed to characterize different sediment types by their velocity‐ and attenuation‐porosity relationships. They demonstrate that terrigenous, calcareous, and diatomaceous sediments cover different velocity‐ and attenuation‐porosity ranges. In terrigenous sediments, P wave velocities and attenuation coefficients decrease rapidly with increasing porosity, whereas S wave velocities and shear moduli are very low. Calcareous sediments behave similarly at relatively higher porosities. Foraminifera skeletons in compositions of terrigenous mud and calcareous ooze cause a stiffening of the frame accompanied by higher shear moduli, P wave velocities, and attenuation coefficients. In diatomaceous ooze the contribution of the shear modulus becomes increasingly important and is controlled 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.