New global map of seismic crust



An up-to-date global compilation of the thickness of the earth's crust and a compilation of upper mantle seismic velocity measurements has been published recently by Soller, Ray, and Brown (Tectonics, 1, 125–149, 1982). The data base indicate 2508 crustal thicknesses and 1806 Pn (uppermost mantle) velocity values. The data are from seismic refraction and surface wave measurements. The compilation represents a significant expansion of available crustal thickness maps, with more uniform coverage. Thus, in agreement with current geophysical interpretations, numerous tectonic features are recognizable as local variations in crustal thickness. For example, mountain chains in isostatic equilibrium, such as the Alps, the Andes, and the Pamir and Tien Shan ranges, display a thickening of the crust and a deeper Mohorovicic Boundary. Beneath the Tibetan plateau, the crust is 80 km thick—the maximum observed. The area of Japan and the Kurile Islands are represented on the map as a thickened crustal ridge separating the thin oceanic crust of the Pacific plate from the thicker crust underlying the marginal basins of the Seas of Japan and Okhotsk. Contours define the Pacific-Eurasion plate boundary, located southeast of the Kurile island arc. Very thin crust, often less than 4 km, occasionally outlines oceanic spreading centers, such as the Midocean Ridge in the North Atlantic.