• Shear wave velocity 



1. The introduction of shear wave velocity and velocity gradients into 

 some, but not all, bottom-loss modeling requires accurate prediction of shear wave 

 velocity versus depth in the sea floor. The shear modulus (which can be derived if shear 

 velocity and density are known) is also an important engineering property of sediments. 

 Accurate prediction of shear velocity versus depth in the full range of marine sediments 

 and rocks requires much more data than now available. 



2. It is recommended that laboratory and in situ measurements of shear 

 wave velocity in marine sediments and rocks be supported. It is further recommended 

 that at-sea measurements be emphasized with instruments, or probes, placed on or in the 

 sea floor. A desirable final result is the profile of shear velocity with depth in the sea 

 floor in the principal types of sediments and rocks. 



• Shear wave attenuation 



1 . Very few studies have been made of the attenuation of shear waves in 

 marine sediments and rocks. In this field, in situ studies should be emphasized with some 

 supporting laboratory work. The profiles and gradient of shear wave attenuation in various 

 common sediment and rock types also require study. 



• Densities of sediments and rocks 



1. Support laboratory and, especially, in situ measurements and studies of 

 density and density profiles and gradients in sea floor sediments and rocks. In situ methods 

 in the past have included measurements with nuclear probes and in boreholes by logging. 

 Density logging in the boreholes of the Deep Sea Drilhng Project should be supported and 

 encouraged. 



2. Results of the laboratory density measurements by the Deep Sea Drilling 

 Project should be studied and supplemented with additional laboratory measurements. 



Atlases, Charts and Other Syntheses 



• The compilation of the following types of regional atlases, charts and other 

 syntheses should be supported and/or encouraged. 



1. Sediment types and properties (including mean grain size, density, 

 porosity, and sound velocity) at the present-day water-sediment interface. Given only 

 sediment type, or mean grain size, we can predict sound velocity and attenuation, and 

 density. 



2. Compilations of acoustic reflection data to show the form, true thick- 

 nesses, interval velocities, and velocity gradients of sediment and rock layers in a given 

 region. This facihtates construction of geoacoustic models and extrapolation of models 

 and experimental data within a region or geomorphic province. 



3. A continued, intensive effort should be encouraged to produce the best 

 possible topographic (bathymetric) charts of the sea floor. This is the overall province of 

 NAVOCEANO and should be strongly supported by other agencies. 



