Possibilities of river seismic survey for studying the structure of the Earth's crust and the upper mantle of the territory of Siberia

A river seismic survey technology based on using pneumatic water sources and autonomous seismic recorders, which are installed on the river bank and configured for continuous seismic recording, is developed at the Geophysical Survey of the Russian Academy of Sciences (GS RAS). In recent years, several thousand kilometers of profiles have been developed by the CDP-2D method on the rivers of East Siberia: Lena, Nizhnyaya Tunguska, and Vitim. Previously, only 6- to 10-s seismograms were used to study the structure of the upper part of the Earth's crust. At the same time, the deep structure of the crust in the vast territories of East Siberia remains poorly understood because of the high cost of research. The river seismic survey data are used on a profile section acquired in the lower reaches of the Lena River to demonstrate the possibility of studying the crustal structure to the full depth, including the Mohorovicic discontinuity. For this purpose, the archival seismic records are reprocessed with the construction of montages of seismograms of increased duration (up to 23 s). The low-amplitude oscillations of reflected waves from deep boundaries are distinguished owing to multiple summation, which is much larger than in conventional seismic surveys. The equipment used in this study has a sufficient dynamic range, and a high multiplicity is achieved by increasing the binning area. Wind noise leads to the inferior quality of time sections of the upper crust but does not worsen the section at great depths, so this material should not be excluded from processing. The river seismic surveys carried out using the technology developed at the GS RAS on the rivers of East Siberia within about 2700 km contain data that make it possible to build deep sections down to the Mohorovicic discontinuity, and this work needs to be done.