Theoretical seismology

An outstanding achievement of the last 4 years in U.S. research into theoretical seismology is the identification of how much information (about earth structure) is contained in a given set of seismic data. This work, an extension of earler successes in inverse theory, should find wide application in other branches of physical science and in the biological sciences. Advances have also been made in studies of the effect of lateral heterogeneities on short‐period waves, the theoretical effect (on seismic waves) of departures from the usual laws of isotropic linear elasticity, the spectral content of short‐period waves by using maximum entropy methods and homomorphic deconvolution, and the use of finite difference and finite element codes. A beginning has been made in the study of wave scattering in random media. These research fields are all fairly new in relation to the traditional occupation of generating theoretical seismograms in ever more complex earth models, assumed to be spherically symmetric; this classical endeavor too has seen breakthroughs in the last 4 years. Seismic source theory, now taking probably more than half the research effort of theoreticians, is reviewed in a separate report.