Velocity structure, composition and discrimination of crustal provinces in the former Soviet Union

Abstract

Significant progress had been made over the last two decades in seismic refraction/wide-angle reflection investigations of continental Russia. Highlights of this progress include the determination of crustal thickness, lithospheric body-wave velocities, compressional and shear wave attenuation, and existence of deeply penetrating dipping reflectors. These new multiwave Deep Seismic Sounding (DSS) data, recorded along geotraverses crossing Precambrian cratons (PC), provinces of Cenozoic basin deposition (CB), and Palaeozoic fold belts (PB), provide a basis for the study of Eurasian continental structure and tectonics. Interpretation of DSS data has shown that geological provinces of different age and tectonic history can be distinguished by the relationship between V p/ V s and the crystalline crustal thickness ( h). There are two primary relationships in the V p/ V s vs. h function. In the first (characteristics of PC), V p/ V s is directly proportional to crustal thickness. In the second relationship, observed in CB and PB, V p/ V s is inversely proportional to crustal thickness. Province boundaries are imaged as dipping reflectors through analysis of the wave field of three component records using special velocity filtering. Dynamic features of these reflections suggest that these boundaries are detachment faults separating relatively thin layers with complicated fine structure. The composition of the crystalline crust, determined from body wave velocities, varies significantly over the transition zone from one geological province to another. Mapping of regions according to the V p/ V s vs. h function, shows a correlation of the known mineral, oil, and gas deposits with province boundaries.