Азимутальная анизотропия Саяно-Байкальской складчатой области по приемным функциям далеких землетрясений

Abstract

The purpose of the work is the determination of a detailed velocity structure of the earth's interior of the seismically active Sayan-Baikal fold region, including the identification of the azimuths and depths in the vicinity of the observation points with anisotropic properties. The source data for the study is the long-term observations by five broadband seismic stations in the Sayano-Baikal fold region. The proposed methodology for identifying the depths and directions of the earth's interior with anisotropic properties is based on the longitudinal receiving function method. The receiving functions for all possible directions of each observation point have been selected from the tele-seismic records. The azimuthal boundaries are identified in relation to the observing station where the receiving functions change significantly, which means a change in the velocity structure when crossing these conditional boundaries. Within the azimuth ranges (BAZ) with homogeneous receiving functions, velocity models (V S ) have been calculated by inverting the functions. The models take into account the relationship between the depth of medium sounding (h) and the corresponding distance from the seismic station (d). Based on the one-dimensional velocity sections for different azimuths, circular models V S (h,BAZ,d) have been constructed with the account of the seismic drift. The models visualize the velocity structure in relation to all observation points at the depths up to 70 km and 270 km. As a result of the study, a set of models reflecting the detailed deep-seated velocity structure of the Sayano-Baikal folded region has been obtained. The velocities of the seismic waves V S ( h ) have been determined within the earth's crust with an average depth step of 1 km, and within the mantle, with a step of 5-10 km. The circular models V S (h,BAZ,d) clearly demonstrate the velocity heterogeneity in various directions from the observation point and allow one to identify the anisotropy of the medium. The latter is manifested as the presence of a symmetry axis in the circular models, which on average has a northwest-southeast orientation, but varies with the depth.