Spatial and Temporal Variations in Sediment Compressional Wave Speed and Attenuation Measured at 400 KHZ for SAX04
Abstract
Diver cores were collected from various locations within the SAX04 site from 21 September to 3 November 2004 and compressional wave speed and attenuation were measured every centimeter at 400 kHz. Although measured values of sound speed and attenuation fall within established ranges for archived data from similar medium quartz sands, fluctuations in measured values were observed in the data that can be explained by the pattern of storm events during the experiment. Three significant storm events occurred during the period in which cores were collected: a category-4 hurricane, a tropical storm, and an early-winter cold front. Following these events values of sound speed initially increased, but then later decreased; values of sound attenuation did not show this pattern, but were generally lower (mean = 92.1 dB/m) than values measured. five years ago at the SAX99 site nearby (mean 177.5 dB/m). Values of sediment sound speed measured at the SAXO4 (mean velocity ratio = 1.162) were generally greater than those measured at the SAX99 site (mean velocity ratio = 1.155). Values of coefficient of variation for sediment sound speed were lower for SAXO4 measurements (0.55%) than SAX99 measurements (0.70%). Lower values of sound attenuation measured at the SAXO4 site was probably due to a lack or absence of shell fragments that may have been segregated by the sediment resuspension and settling during and after storms. The roles of sediment transport, grain size, grain sorting, porosity, and density in controlling sediment compressional wave speed and attenuation at the SAXO4 site are discussed.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2005
- Accession Number
- ADA450983
Entities
People
- Kevin B. Briggs
- Michael D. Richardson
- Michael Zimmer
Organizations
- United States Naval Research Laboratory