Seismic studies of lateral variations in the lithosphere and asthenosphere have been major contributors to current understanding of plate tectonics. Plate tectonics, in turn, has provided a reference frame for deciphering present and past geological processes that have formed natural resources. For example, the huge oil fields of the Middle East, in part, resulted from a collision of the African and Eurasian plates. The tectonic processes involved included subduction of oceanic lithosphere under Eurasia, continental collision to form the Zagros mountains, and the forces of this collision gave rise to structural traps for oil. However, currently there is recognition that intraplate orogenic activity does not fit into the plate tectonic scheme.
A number of geological processes do not fit the plate tectonic model of undeformable plates which interact only at the boundaries. Among these are intraplate extension, such as the Basin and Range of North America or the east African rift system, intraplate earthquakes such as the New Madrid event in 1812, or intraplate volcanoes such as kimberlite pipes, the source of diamonds. Further seismic studies are required to elucidate these processes.
Tomographic studies have been used to delineate high temperature zones in the lithosphere which can be important for geothermal energy and in the production of minerals. Anisotropy studies tell us how flows in the mantle redistribute the heat and concentrate it at the surface. Understanding the distribution of the Earth's internal heat is, in turn, important to the understanding of the maturation of hydrocarbons in sedimentary basins, or inferring conditions, now and in the past, favorable for generating minerals in hydrothermal zones. Implementation of this information involves developing exploration strategies for natural resources and economical methods of extraction of resources.
The study of the distribution of seismic velocities in the lithosphere and asthenosphere is also important to practical problems of understanding the forces generating earthquakes and how to predict the damaging effects of earthquakes as a function of velocity variation along the propagation path taken by the seismic waves.
Acknowledgments. This work was supported by the National Science Foundation grant EAR-8708371.