CONSTRUCTION OF EARTH CRUST SECTIONS DOWN TO THE MOHO BOUNDARY BASED ON LOW AMPLITUDE REFLECTED WAVES OF RIVER SEISMIC SURVEY USING CPD-2D METHOD (<i>Vitim River, junction zone of the Angara-Lena monocline of the Siberian platform and the Bodaibo-Pat

In 2019, employees of the Research and Production Enterprise Luch jointly with specialists of the Seismological Branch of the Geophysical Survey of the Russian Academy of Sciences (GS RAS) carried out river seismic exploration works using the common depth point method (CDP-2D) along a 170 km long profile in the lower reaches of the Vitim River. The research was carried out according to the original methodology developed in the Siberian branches of the GS RAS, using the Baikal instruments recording seismic signals continuously (in contrast to traditional cable bottom or ground-based systems with time-limited recording). In this case, patented Malysh air guns were used in the water for the excitation of elastic waves, which have been recorded by ground registration method on the riverbank. To this day, the archives store primary materials from each receiving point (about 7000, with a distance of 25 m between them) in the form of a continuous hours-long digital recording of seismic signals and noise. These materials make it possible to generate seismograms of significant duration – up to 23 s, equal to the time interval between wave generations, in contrast to 6–10 second seismograms traditionally used to construct sections of the upper part of the Earth’s crust. In addition, the 24-bit Baikal recorder makes it possible to record signals with an amplitude two orders of magnitude lower than the amplitude of seismic noise. On the seismic sections constructed by the processor at arrival times of up to 13–14 sec, due to an increase in the stack fold of signals up to 1000–2000, we can select low-amplitude waves, reflected from boundaries in the middle and lower parts of the Earth’s crust to the Moho boundary. High fold is achieved by increasing the size of the stacking site (bin) by several times. By processing seismograms, generated from archival materials, for the first time, we have a complete vertical section of the Earth’s crust along a 170 km long profile, using low-amplitude signals. The profile passes through the junction zone of the Angara-Lena monocline and the Bodaibo-Patom folded system. The proposed approach can be used to obtain preliminary (and relatively cheap) information about the deep structure of the Earth’s crust along profiles performed using the CDP-2D river seismic exploration method.