MARINE GEOPHYSICS AND ITS IMPACT ON DEVELOPMENT OF MARINE GEOLOGY

The establishment of Palate Tectonics marked the revolution of earth sciences in 1960s. Marine geophysics and marine geophysicists made great contribution to the revolution. During the Second World War, the development of marine technology was prioritized by both sides of the war. After it up to 1960s, extensive geophysical surveys had been carried out at seas, and a great amount of data acquired with many new discoveries. For examples, it was found that the earthquake zone in the mid-ocean is in fact a rifting valley; the marine magnetic anomalies are symmetry on both sides of the oceanic mid-ridges; the sediments on the ocean floor are thin, and gradually thicken on both sides of the ridge; the oceanic crust is only several kilometers thick, but the continental crusts could reach a thickness over 30km; the heat flow at the mid-ridges is higher than expected, and decreases on both sides as the distance from the ridge increases; the seismic velocities increase from surface to 80km, and reduce from 80km to 150km of depth. The upper part is thus called lithosphere, and the lower part called asthenosphere; the earthquake epicenters are distributed along a zone dipping at 45 from the trench down to over 700km below the land, it is the subduction zone of the oceanic lithosphere. The discoveries mentioned above brought about a big change of scientific philosophy and paved the way for the theory of plate tectonics.