Geophysical research: article

Аnnotation: We consider some possibilities to extract additional information on the velocity structure of the upper crust on reference geophysical profiles. The CDP observation system is very dense and gives the information on the reflecting boundaries in the crust and upper mantle. The travel-time curve length of 10 km with a gap between receivers of 50 m and source sampling of 100 m result in tremendous amounts of data (more than 3 million of seismic traces); therefore, the manual processing of refraction waves becomes impossible. To obtain information on refracting horizons automatically, we apply the dynamic conversion of head waves that filters coherent wave fields along one of the spatial directions. We address the issues related to the influence of the profile curvature, topography, and refraction of head waves into the underlying layer on the results of the dynamic conversion. It is proved that these factors affect the conversion result as low-frequency filters. It is shown that for conditions of the 3-DV profile central part, their influence on the dynamic conversion of the CDP and DSS data is slight: the decrease in head wave amplitudes does not exceed 13 % in the frequency range from 13 to 25 Hz; whereas the effect is more pronounced for the refraction seismic data. Based on the CDP data from the 3-DV profile central part (700 km long), we constructed time sections of longitudinal waves, as well as shear head waves and multiple reflected refractions in different tectonic areas of the Siberian Platform: the Middle Lena monoclise, the Vilyuy syneclise, and the Lower Aldan depression. Time sections of the refracted waves provide information on the boundaries in the sedimentary cover and on the crystalline basement. The structure of the crust is studied to a depth of about three kilometers.