Refinement of the velocity section sedimentary stratum by the Nakamura method at new seismic stations of the IDG RAS

In 2017, as part of a project to study the deep structure of the central part of the East Europe-an platform, IDG RAS staff installed a sub latitudinal seismic profile of about 500 km in length, consisting of six stations. To successfully solve the problem of restoring a deep velocity section, the fullest possible information is needed on the velocity characteristics of the sedimentary sequence and, in particular, the first 0.5-1 km. Despite the considerable knowledge of the geological structure of the Moscow syneclise, information about its speed structure is based on interpolation and is fragmentary in nature. The paper presents the results of studies of the upper part of the sedimentary cover of the central part of the East Eu-ropean Platform (EEP) according to the data of the new network of broadband seismic stations IDG RAS. Using seismic noise records for each station, the dominant frequency peaks were obtained by the Nakamura method. For the Mikhnevo and Shatura stations, based on the data of deep drilling, it was established that the dominant peak corresponds to the boundary of the Upper Devonian - Lower Carbonian sediments. The obtained results make it possible to trace the occurrence of the indicated boundary along with all stations of the network along with the sublatitudinal profile through the collision zone of the EEP.

VELOCITY MODEL OF THE UPPER MANTLE OF THE FLANKING PLATEAUS OF MID-OCEANIC RIDGES

A new element is included in the study of velocity sections of the upper mantle of regions of continents, oceans, and transition zones with different endogenous regimes (according to the advection-polymorphic hypothesis — APH). This is the flanking plateaus (FP) of the mid-ocean ridges (MOR). It is assumed that these regions underwent the process of oceanization in the Mesozoic along with other parts of the oceans. In the Neogene MORs were formed. Significant parts of the basins were engulfed in modern activation, including magmatism. Between these parts of the oceans, relatively narrow strips (200—300 km wide) have survived, which some authors refer to as flanking plateaus. They are located at the edges of the MOR. FP did not experience young activization. This is indicated by the features of the bottom topography, magnetic, gravitational and thermal fields, and a velocity section of the upper horizons of the mantle. An element of checking the nature of the FP can be the construction of a velocity section of the mantle beneath these regions. According to the APH, it should differ from the neighboring ones by the increased velocity of seismic waves in the upper about 200 km. The experimental data for such work turned out to be extremely small. It was possible to build only one travel-time, using data on the southern part of the Atlantic Ocean. Insignificant information was also attracted on the southern part of the East Pacific Rise and the Mid-Indian Ridge. The travel-time corresponds to the velocity section, which completely coincides with the forecast. The latter was calculated according to the heat and mass transfer scheme in the APH version and the thermal model of the mantle. The velocity section of the FP mantle does not contain indications of a partial melting layer. Consequently, there should be no manifestations of young magmatism in FP. Verification showed that in most of the studied fragments of MOR this is true.