Instrumentation for crosshole geoacoustic measurements in unconsolidated sediments

Abstract

Research tools are described that enable direct measurements of sediment properties as a function of depth in unconsolidat,ed sediments. The first tool is a hole making device that sits on the sea floor and utilizes pneumatic and hydraulic forces to remove the sediment from the interior of a cylindrical tube. 25 cin in diameter and 6 111 deep. This hole can be used to permanently

deploy instru~nentss uch as seismometers. or it can be lined with a plastic tube as a casing, for subsequent access and the temporary deployment of geoacoustic logging instruments. Two such instruments are described. One is used to measure sound velocity and attenuation for compressional waves while the other nleasures these parameters for shear waves. The design, development and initial tests of these devices is presented.