John E. Nafe

Variation with depth in shallow and deep water marine sediments of porosity, density and the velocities of compressional and shear waves

In a study of the dependence of the velocity of compressional waves in marine sediments upon the thickness of overburden, the velocity‐depth relationship in shelf sediments is shown to be distinctly different from that in deep basin sediments. The difference between the two cases may be illustrated by comparing the straight lines that best represent the data. These are V=1.70Z+1.70, shallow water, V=0.43Z+1.83, deep water where V is in km/sec and Z is in kilometers. Shallow and deep water are defined arbitrarily to be under 100 fathoms and over 1,500 fathoms respectively. The observed variation of average compressional velocity in the shallow and deep water sediments, taken together with the known limited range of variation of velocity for a given porosity, yields limits in turn upon the porosity‐depth dependence in the two environments. It is shown that at the same depth of overburden porosity is much greater in deep water sediments than in shallow. A physical argument is presented to show that there is ...

Physical analysis of deep sea sediments

A sonic pulse system, similar to that used at Lamont Geological Observatory for seismic model experiments, was used aboard the Research Vessel VEMA during the summer of 1954 to determine high frequency seismic velocities in fresh deep sea sediment cores. Velocity profiles were obtained from 26 cores covering a wide range of lithologies and ages (Recent to Miocene). Density, porosity, median grain size, sorting, carbonate content, and salt content were also measured. The compressional wave velocity in the ocean‐bottom unconsolidated sediments studied is well represented by the equation: v′=2.093-(.0414±.0060)ϕ+(.00135±.00038)γ-(.44±.15)η where v′=compressional wave velocity in km/sec ϕ=median grain size in phi units γ=percentage of HCl soluble material η=porosity. Many measurements gave velocities less than the velocity of sound in sea water. Most of the low carbonate samples followed a velocity‐porosity relation given by the Wood (1941) equation. The regression coefficient, −.44η, agrees well with the ave...

Geophysical investigations in the area of the Perth Basin, Western Australia

Marine geophysical investigations in the area of the Perth Basin lead to proposed changes in the structural control of the basin and of the structure within the basin. The main north‐south graben structure appears to be crossed by a series of major faults which trend roughly north‐northwest. A broadening of the basin to a width of just over 100 km (65 miles) to the west in the area between Perth and Harvey, which was earlier indicated by aeromagnetic results, appears to be produced by two such faults: The southern fault does not cross the graben but merges with it in the form of the Dunsborough Fault; the proposed northern fault crosses the graben to produce a break in continuity of the Darling Fault which marks the eastern margin of the basin. The northern fault appears to have caused a division of the main sedimentation axis of the Perth Basin into two near parallel axes within the widened section of the basin. The Dandaragan Trough which forms the eastern axis now appears to terminate at the Darling Fa...