. The Earth beneath the sea : History . COMPUTED P'I03 p'28') P'3Z7 STRUCTURE SECTION I J \ Fig. 18. Crustal section across continental margin near San Diego, California. (After Worzel and Talwani, unpublished.) at the continental edge, which here occurs about 200 km from the shorehne at about the 1000-fm curve. Thompson and Talwani (1959) have computed a section across the continental margin along the west coast of the United States, near San Francisco. The densities used are shown in the section illustrated in Fig. 19. The section is complicated by the various mountain ranges in that coastal
. The Earth beneath the sea : History . COMPUTED P'I03 p'28') P'3Z7 STRUCTURE SECTION I J \ Fig. 18. Crustal section across continental margin near San Diego, California. (After Worzel and Talwani, unpublished.) at the continental edge, which here occurs about 200 km from the shorehne at about the 1000-fm curve. Thompson and Talwani (1959) have computed a section across the continental margin along the west coast of the United States, near San Francisco. The densities used are shown in the section illustrated in Fig. 19. The section is complicated by the various mountain ranges in that coastal region. The abrupt change of crustal thickness at about the 1000-fm curve is again evident. B. Mid-Ocean Ridges The only mid-ocean ridge examined in detail is the Mid-Atlantic Ridge at about latitude SO'^N. Fig. 20 shows, at the top, a continuous gravity curve obtained with the Graf Sea Gravimeter in crossing this feature, and. at the bottom, the topography. After the effect of the topography (Talwani. Heezen and Worzel, 1961) has been removed, an anomaly (Bouguer) is obtained which must be explained by densities within the crust or the mantle. There were some seismic measurements available to provide some control for the upper part of the crust (Ewing and Ewing, 1959). Fig. 21a shows the resulting section for the conventional view that the variation of the thickness of the crust is primarily responsible for the remaining anomaly. Even with the abrupt change of depth
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