. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 1] THE MAGNETIC FIELD OVER THE OCEANS 211 EXPLANATION 162° 30'. Contours showing flighliine inter- sections 11° 40' 11° 30' 11° 20 162° 20 Contour interval 50 gommos Uncorrected for regionol grodient Fig. 25. Magnetic map of Eniwetok. (After Keller et ah, 1954, fig. 7.) Keller et al. (1954) conclude that the anomalies observed across the Aleutian Trench are produced by susceptibility contrasts within the rocks of the sea floor and bear no direct relation to the trench. However, they could also arise from variations i
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 1] THE MAGNETIC FIELD OVER THE OCEANS 211 EXPLANATION 162° 30'. Contours showing flighliine inter- sections 11° 40' 11° 30' 11° 20 162° 20 Contour interval 50 gommos Uncorrected for regionol grodient Fig. 25. Magnetic map of Eniwetok. (After Keller et ah, 1954, fig. 7.) Keller et al. (1954) conclude that the anomalies observed across the Aleutian Trench are produced by susceptibility contrasts within the rocks of the sea floor and bear no direct relation to the trench. However, they could also arise from variations in the depth of the basement rocks under the sea floor. In the absence of information from other sources, for example seismic measurements, it is impossible to decide between these two alternatives. In the case of the Tonga Trench the magnetic measurements were supported by echo-sounder profiles and by several seismic sections. Fig. 29 shows a possible interpretation of the magnetic profiles in terms of a magnetic basement, taking into account these other sources of information. Although this approach cannot be expected to lead to precise values for the thickness of the sediments, it does give a qualitative picture of how the thickness might vary from place to place. The discrepancy between the observed and comj)uted curves cannot be. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hill, M. N. (Maurice Neville), 1919-. New York : Interscience Pub.
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