Seismic refraction shooting in an area of the Eastern Atlantic

For the experiments described in this paper a new method of seismic refraction shooting was developed. With this method hydrophones suspended at a depth of about 100 ft. below the surface of the sea acted as receivers for the compressional waves developed by depth charges exploding at a depth of approximately 900 ft. The hydrophones were connected with sono-radio buoys which radio-transmitted the electrical signals to a recording system in the ship from which the charges were dropped. Four buoys were in use simultaneously, distributed at differing ranges from the ship. The experiments were carried out at three positions in an area of the eastern Atlantic around the point 53° 50' N, 18° 40' W, where the water depth is approximately 1300 fm. (2400 m). The results showed that the uncrystalline sedimentary layer in this area varied in thickness from 6200 ft. to 9700 ft. (1900 to 3000 m), and that the velocity of compressional waves in it increased from the value for sea water, 4900 ft./s (1.5 km/s), at the surface with an approximately constant gradient of 2.5/s to a limiting value of 8200 ft./s (2.5 km/s). Below the sedimentary layer there was a crystalline rock with compressional wave velocity of approximately 16500 ft./s (5.0 km/s) and of thickness varying between 8800 ft. (2700 m) and 11100 ft. (3400 m). The base of this layer was in both determinations at approximately 25500 ft. (7800 m) below sea-level. The lowest layer concerning which information was obtained gave a value for the compressional wave velocity of about 20500 ft./s (6.3 km/s), but was of undetermined thickness. The characteristics of the sedimentary layer were such as might be expected for a continuous succession of deep-sea sediments, the thickness on this basis being such as to indicate the long existence of the ocean in this area. On the other hand, it is possible that it represents a downwarped continental shelf. The layer below the sedimentary layer has a compressional wave velocity which is low for an igneous rock at this depth, and it is probable that it represents a crystalline sedimentary rock. From the evidence it is not possible to determine whether this rock is of continental or deep-sea origin. The lowest layer of these experiments is unlikely to have a constitution similar to that of the European granitic layer, since the compressional wave velocity in it would, on this hypothesis, be exceptionally high. The value is, however, close to that calculated by Jeffreys for the intermediate layer.

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VELOCITY OF COMPRESSIONAL WAVES IN POROUS MEDIA AT PERMAFROST TEMPERATURES

Geophysics ◽

10.1190/1.1439954 ◽

1968 ◽

Vol 33 (4) ◽

pp. 584-595 ◽

Cited By ~ 81

Author(s):

A. Timur

Keyword(s):

Porous Media ◽

Wave Velocity ◽

Compressional Wave ◽

Freezing Process ◽

Rock Matrix ◽

Compressional Wave Velocity ◽

Compressional Waves ◽

Average Equation ◽

Wave Velocities ◽

Time Average

Measurements of velocity of compressional waves in consolidated porous media, conducted within a temperature range of 26 °C to −36 °C, indicate that: (1) compressional wave velocity in water‐saturated rocks increases with decreasing temperature whereas it is nearly independent of temperature in dry rocks; (2) the shapes of the velocity versus temperature curves are functions of lithology, pore structure, and the nature of the interstitial fluids. As a saturated rock sample is cooled below 0 °C, the liquid in pore spaces with smaller surface‐to‐volume ratios (larger pores) begins to freeze and the liquid salinity controls the freezing process. As the temperature is decreased further, a point is reached where the surface‐to‐volume ratio in the remaining pore spaces is large enough to affect the freezing process, which is completed at the cryohydric temperature of the salts‐water system. In the ice‐liquid‐rock matrix system, present during freezing, a three‐phase, time‐average equation may be used to estimate the compressional wave velocities. Below the cryohydric temperature, elastic wave propagation takes place in a solid‐solid system consisting of ice and rock matrix. In this frozen state, the compressional wave velocity remains constant, has its maximum value, and may be estimated through use of the two‐phase time average equation. Limited field data for compressional wave velocities in permafrost indicate that pore spaces in permafrost contain not only liquid and ice, but also gas. Therefore, before attempting to make velocity estimates through the time‐average equations, the natures and percentages of pore saturants should be investigated.

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DEPENDENCE OF IN‐SITU COMPRESSIONAL‐WAVE VELOCITY ON POROSITY IN UNSATURATED ROCKS

Geophysics ◽

10.1190/1.1440249 ◽

1972 ◽

Vol 37 (1) ◽

pp. 29-35 ◽

Cited By ~ 29

Author(s):

Joel S. Watkins ◽

Lawrence A. Walters ◽

Richard H. Godson

Keyword(s):

Wave Velocity ◽

Seismic Refraction ◽

Compressional Wave ◽

Unconsolidated Sediments ◽

Compressional Wave Velocity ◽

Near Surface ◽

Least Squares Fit ◽

Water Saturated ◽

Porosity Range

The relation of in‐situ compressional‐wave velocities to porosities, determined by seismic refraction for unsaturated near‐surface rocks from different areas in Arizona, New Mexico, and California, is grossly similar to relations determined by other investigators for water‐saturated rock and unconsolidated sediments. The principal difference is that in the porosity range 0.0–0.2, compressional waves travel somewhat more slowly in unsaturated rocks than in water‐saturated rocks, and much more slowly, in the porosity range 0.2–0.8. The function, ϕ=−0.175 ln (α)+1.56, where ϕ is the fractional porosity and α is the compressional‐wave velocity, was obtained as a least squares fit to the experimental data. Bulk densities are reported for all samples; moisture contents are reported in some instances.

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PHYSICAL ANALYSIS OF DEEP SEA SEDIMENTS

Geophysics ◽

10.1190/1.1438417 ◽

1957 ◽

Vol 22 (4) ◽

pp. 779-812 ◽

Cited By ~ 51

Author(s):

George H. Sutton ◽

Hans Berckhemer ◽

John E. Nafe

Keyword(s):

Grain Size ◽

Wave Velocity ◽

Deep Sea ◽

Compressional Wave ◽

Coarse Grained ◽

Unconsolidated Sediments ◽

Physical Analysis ◽

Seismic Velocities ◽

Compressional Wave Velocity ◽

Wide Range

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: [Formula: see text] 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 average slope of the Wood equation over the observed porosity range. High carbonate and large median grain size samples gave velocities above that predicted by the Wood equation. These higher velocities are explained as the combined result of shear strength and low effective porosity in the samples. The highest velocities were found in slowly deposited sediments. The degrees of sorting of the sediments had no observable effect on the seismic velocities except that unexplained variations were greater for more poorly sorted materials. No correlation between velocity and age was evident in the sediments studied. The effect of temperature, between 40 and 80°F. on compressional velocity in sediments may be explained by changes in elastic properties of the water fraction alone. The effect of compaction in the upper 15 or 20 feet of homogeneous sediments produced a change in seismic velocity not greater than 1 or 2 percent. Attenuation was greater in the coarse‐grained high‐velocity sediments than in sediments of smaller grain size.

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THE LITHOSTRATIGRAPHY OF THE NEAR-SURFACE IN PART OF SEDIMENTARY KOLMANI FIELD IN NORTHERN BENUE TROUGH, NIGERIA, USING SOIL CORE AND SEISMIC REFRACTION DATA

Earth Sciences Pakistan ◽

10.26480/esp.02.2020.53.59 ◽

2020 ◽

Vol 4 (2) ◽

pp. 53-59

Author(s):

Glory G. Akpan ◽

Etim D. Uko ◽

Owajiokiche D. Ngerebara

Keyword(s):

Wave Velocity ◽

Seismic Refraction ◽

Compressional Wave ◽

Soil Samples ◽

Soil Core ◽

Compressional Wave Velocity ◽

Near Surface ◽

Weathered Layer ◽

Seismic Refraction Data ◽

Refraction Data

Soil samples from 31 shallow boreholes were acquired at depths 0m, 1m, 2m, 3m, 4m, 5m, 7m, 10m, 15m, 20m, 25m, 30m, 35m, 40m, 45m, 50m, 55m, and 60m in Pingida (Kolmani Field) in Ako LGA, Gombe State, Nigeria. Using the same boreholes, seismic refraction data was also acquired. The aim of the survey was to delineate the near-surface lithology and velocity layering. The boreholes were drilled using rotary drilling rig and the core samples acquired and described using Wentworth Scale. Seismic refraction data acquired using a single trace Stratavisor NZXP portable digital recorder. The recording spread consisted of a single SM4- 10Hz geophone positioned at depths where the soil samples were taken. A hammer was used as the energy source and placed 3m away from the hole to obtain the first breaks. The refraction data was interpreted using UDISYS Version 1.0.0.0 software. The soil layers in the Kolmani Field have three distinct layers specified as follows, namely, top weathered and sub-consolidated layers made up of intercalation of sandstone, gravel ash clay and muddy coal shale. The lithologic strata do not correlate throughout the field resulting from the highly variable elevation which ranged from 317m and 524m with average of 389.16m. The top weathered layer of laterite intercalated with cobblestones with compressional wave velocity ranging from 342 ms-1 to 517 ms-1 with an average of 405.03 ms-1. Beneath the weathered layer is the sub-consolidated Clay layer intercalated with silt and laterite of compressional wave velocity ranging from 440 ms-1 to 1854 ms-1 of average of 826 ms-1. The underlying consolidated layer is the shale and coal layer having compressional wave velocity ranging from 1518 ms-1 to 4201 ms-1 with an average of 2162.65 ms-1. The dominant lithologic sequences encountered are laterite, clay, silt, sand, gravel, coal and shale. The results of this work can be used for static corrections in seismic reflection processing, planning and assessing risk for engineering structures, and for groundwater exploration. The laterite, clay, silt, sand, gravel, coal and shale can be utilized in agriculture, construction, process industries, and environmental remediation.

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THE PROPAGATION OF THE COMPRESSIONAL WAVE IN THE CRUST: II. SYNTHETIC SEISMOGRAMS

Canadian Journal of Earth Sciences ◽

10.1139/e65-042 ◽

1965 ◽

Vol 2 (6) ◽

pp. 560-576 ◽

Cited By ~ 2

Author(s):

M. J. Keen ◽

C. F. Tsong

Keyword(s):

Nova Scotia ◽

Wave Velocity ◽

Atlantic Coast ◽

Compressional Wave ◽

Synthetic Seismograms ◽

The Other ◽

Compressional Wave Velocity ◽

Compressional Waves ◽

The One

Synthetic seismograms have been generated in an attempt to measure the attenuation of compressional waves beneath the Atlantic coast of Nova Scotia; the results suggest that the value of Q must be of the order of 300 whatever the mechanism of propagation may be. Comparison with results of experiments in the Gulf of St. Lawrence shows that attenuation of first events in the range of distance up to 60 km is more rapid in the rocks beneath the Gulf than in those beneath the Atlantic coast of Nova Scotia, This may be due either to attenuation in the upper sedimentary layers, present in the one place but not in the other, or to greater attenuation within rocks in which the compressional wave velocity is the same as in those beneath the Atlantic coast.

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Investigation of Weak Sandstones

Geological Society London Engineering Geology Special Publications ◽

10.1144/gsl.eng.1986.002.01.38 ◽

1986 ◽

Vol 2 (1) ◽

pp. 199-205

Author(s):

L. Dobereiner ◽

M. H. de Freitas

Keyword(s):

Compressive Strength ◽

Moisture Content ◽

Uniaxial Compressive Strength ◽

Wave Velocity ◽

Compressional Wave ◽

Weak Rock ◽

Index Test ◽

Compressional Wave Velocity ◽

Compressional Waves ◽

Weak Sandstone

AbstractIt is proposed that coverage of the class of material described in BS 5930 as weak rock, is in need of improvement.Results from research into the behaviour of weak sandstone (0.5-20 MPa uniaxial compressive strength) are presented to illustrate this need. The strength, deformability, and propagation of compressional waves are reported for weak sandstones and recommendations presented for describing these materials and for testing their strength and deformability. Problems associated with the measurement of compressional wave velocity are also considered.An index test for assessing the strength of weak sandstone (the index of vacuum saturated moisture content) is described and presented.

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On: “EFFECT OF POROSITY, GRAIN CONTACTS, AND CEMENT ON COMPRESSIONAL WAVE VELOCITY THROUGH SYNTHETIC SANDSTONES” BY ANDRIS VIKSNE, JOSEPH W. BERG, JR., and KENNETH L. COOK (GEOPHYSICS, FEBRUARY, 1961, PP. 77–84).

Geophysics ◽

10.1190/1.1439089 ◽

1962 ◽

Vol 27 (5) ◽

pp. 720-721

Author(s):

L. P. Stephenson ◽

R. D Tooley

Keyword(s):

Experimental Data ◽

Wave Velocity ◽

Cement Content ◽

Compressional Wave ◽

Experimental Measurements ◽

Compressional Wave Velocity ◽

Rigorous Analysis ◽

Compressional Waves

The experimental data reported by Viksne, Berg, and Cook have been reinterpreted in the light of a more rigorous analysis of the variables. Since the experimentally determined velocities of compressional waves in the synthetic cores can be described analytically in terms of the porosity and cement content alone with an accuracy comparable to that expected of the experimental measurements, it is not possible to establish what influence manufacturing pressure may have on velocity (other than that resulting from its effect on porosity). In particular, it cannot be said that the reported experiments have demonstrated that grain‐to‐grain contacts affect the velocity in any way. These conclusions are substantially different from those drawn from the same data by Viksne, Berg, and Cook.

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