Seismogravimetric method: principles, algorithms, results

Abstract

SUMMARY A seismogravimetric problem has been posed and solved by a new method which permits the construction of consistent velocity and density models for the Earth's crust and upper mantle based on observations of the seismic and gravity fields. The seismogravimetric method involves a two-step solving procedure. At the first step, a velocity model, V, is constructed as a result of the formulation and solution of the inverse kinematic seismic problem for the velocity increments to a certain known normal velocity Vo. At the second step, the obtained velocity model, V, is transformed, consistent with the known velocity-density relations σ(V), to the density model σ, whose gravity field is calculated. Using the difference between the observed and calculated gravity-field magnitudes we solve the inverse gravimetric problem for the correction rσ to density σ. As a result, the relation σ(V) is refined for the main blocks of the geologic sequence studied. If the density model does not quite fit the observed gravity field, or does not agree with the geological data available, the entire process of solving the problem is repeated, taking account of the results obtained previously. The inverse seismic and gravimetric problems formulated are reduced to sets of linear equations. To solve these, a stable iteration technique has been developed which is intended for specific geophysical problems and serves as a computational basis for the seismogravimetric method. The applicability principles of the seismogravimetric method are described. The method has been tried in special tests and on practical material. The test problem ‘Moscow’ has been chosen as a model example. The efficiency of the method when applied to practical observations is illustrated by interpretation of the DSS data obtained on the Kiev-Gomel’ (Ukraine-Byelorussia) line.