Deep seismic reflections near the SG4 borehole, central Urals

Abstract

Abstract A 7.5 km long seismic reflection profile across the Urals SG4 deep borehole in the Tagil Synform, processed to 17.5 seconds two way traveltime (TWT), provides evidence of a highly reflecting crust at several levels, particuarly in the upper 1–4 s and at 8–10 s. In general, the reflectors dip at low to moderate angles eastwards. Below 10s, reflections are less well defined, but nevertheless exist down to the end of the processed section. This lower part (c. 20 km thick) corresponds to the deep root of the anomalous lower crust reported by previous authors on the basis of refraction velocities (vp c. 7.2–7.8 km/s) and gravity data. The moderately east dipping reflections in the upper crust can readily be correlated with lithologies of the Tagil Synform consisting of volcanic and sedimentary rocks of high contrast in acoustic impedance. The sub-horizontal reflectors at 8–10s are superficially similar to those recorded in Variscan western Europe and interpreted there to relate to the Moho. Thus, the results of this short profile indicate that future CDP profiling across the Uralide Orogen will contribute significantly to an understanding of the structure and tectonics of the orogen.