=2- The principles used in scientific studies of earthquakes are the basic principles of physics and mechanics. With reliable determinations of physical properties and the laws governing generation of seismic disturbances, their propagation, attenuation and effects, applications in seismology have been extended to many other areas of usefulness to mankind. APPLICATIONS OF SEISMOLOGY The most general application of the principles of seismology and one of the first to be accomplished has been determination of the internal constitution of the earth. With increased amounts of seismic measurements of improved accuracy, models of the earth have been successfully devised and tested. In general terms, we now think of the earth as a spheroid with three unequal axes, comprised of a central core, surrounded by a concentric thick mantle and covered on the outside with a thin crust. Details of the interior of the earth are still subjects of discussion and form the basis of continuing programs of worldwide seismic investigations. A second area in which applications of seismology have been fruitful employs chemical explosives to generate seismic disturbances. These are propagated to various depths in the crust and used as yardsticks for measurements of crustal features. The principal elements of the crust are physical properties, geologic structure, stratigraphy and the distribution of these features throughout the total crustal eniDOEARCHIVES The economic benefits of exploration seismology are unprecedented. With modern seismographic tools and procedures, the future reserves of 22