Syntetyczne opracowanie wyników pomiarów prędkości fal sejsmicznych dla Polski północnej i jego zastosowanie do obliczeń głębokości granic sejsmicznych

Abstract

ANALYSIS OF RESULTS OF SEISMIC WAVES VELOCITY MEASUREMENTS FROM NORTHERN POLAND AND THEIR APPLICATION IN ESTIMATIONS OF THE DEPTH OF OCCURRENCE OF SEISMIC BOUNDARIES Summary On the basis of well-logging data from 415 deep drillings in the northern Poland, the Quaternary-Cambrian sedimentary deposits are• divided into 5 velocity complexes, essentially differing in changes of velocity along with depth. Dependence of the interval time ΔT on thickness of the complexes, ΔH, and depth of their occurrence was analysed. The results obtained show that the Triassic strata not covered by Cretaceous and Jurassic strata at present, previously occurred at depths 700 m greater than they do at present. Coefficients characterizing differences between velocity value obtained for a given borehole and mean velocities of the complexes (with thickness and velocity transformed to zero) were calculated. The coefficients were used in preparation of maps making possible to take into account vertical and horizontal velocity gradients. The regularities in velocity changes were determined. These regularities made it possible to propose a formula for calculating the depth of occurrence of seismic boundaries using computer techniques.