EARTH/Crust 405 Figure Diagram showing the recycling of the crust by subduction After Edwards K and Rosen B (2000) From the Beginning London: Natural History Museum Figure Area and volume proportions of the major crustal types From Plate Tectonics and Crustal Evolution by K C Condie (1976) Reprinted by permission of Elsevier Ltd eroded underworks – chains of calc-alkaline batholiths (e.g., Peru) Trenches: the outer margin of subduction zones; the deepest parts of the oceans Ocean basins/abyssal plains: the extensive flat, deep areas of oceans, beyond continental slopes Marginal basins: small basins separating arcs, or landward from arcs (back-arc basins) Inland seas: seas within continents (e.g., Caspian) The relative area and volume of the major crustal types are shown in Figure Crustal Structure We can broadly determine the contrasting layers in the crustal structure by means of seismic wave velocities, determined from earthquake waves and artificial (e.g., nuclear) explosions This shows us