Construction of the earth's crust sections to the Moho boundary by low-amplitude reflected waves of river seismic exploration using the CDP-2D method (Vitim river, the junction zone of the Angara-Lena monocline of the Siberian platform and the Bodaibino-Patom folded system)
In 2019, employees of the Research and Production Enterprise "LUCH" jointly with specialists of Seismological Branch of the 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 by the Siberian branches of the GS RAS, using the "Baikal" equipment recording seismic signals continuously (in contrast to traditional cable bottom or ground-based systems with time-limited recording). In this case, the excitation of elastic waves is carried out in water by the patented air guns "Malysh", they have been recording 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 sec, equal to the time interval between excitations, 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" recording equipment 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 increasing of CDP fold 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 CDP fold, at the same time, is achieved by increasing the size of the summation site (bin) by several times. By the results of processing seismograms, generated from archival materials, for the first time we have got a complete vertical section of the Earth's crust along a 170 km long profile, using low-amplitude signals. The profile is passing through the folded-thrust zone of the Angara-Lena monocline and the Bodaibino-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 the profiles that will be performed using the CDP-2D river seismic exploration method.
