Deep Velocity Sections of the Avacha Bay Area of the Kamchatka Peninsula Obtained by the Receiver Function Method

Abstract

The article studies the structure of the Earth’s crust and upper mantle of the Avacha Bay region of the Kamchatka Peninsula. One-dimensional sections of the dependence of seismic velocities on depth, obtained during the study are presented. These sections are constructed according to the data of the Petropavlovsk (PET), Dalniy (DAL), Institut (IVS), and Karymshina (KRM) stations for the period from 2000 to 2019. The stations are part of the permanent observational network of seismic stations of the Kamchatka Branch, Geophysical Survey, Russian Academy of Sciences. The sections are constructed to a depth of 300 km, which makes it possible to characterize the structure of the medium in the bay area, namely, to identify structural layers in the crust, the Moho boundary, and to estimate the degree of deviation of seismic wave velocities in the upper mantle from the corresponding values of the IASP91 global Earth model. The average values of velocities calculated from the obtained sections in the crust and upper mantle were significantly lower compared to the global model. The average deviation of the observed velocities from the model ones is 0.5–1.0 km/s in the crust, then it gradually decreases to a depth of about 180 km. At greater depths, the velocities in the obtained models coincide with the standard values. It should be noted that at the locations of the seismic stations, the lower boundary of the subducting Pacific Plate runs at depths of about 180 km. Therefore, the main reason for the difference in velocities is probably related to significant heating of material and the complex fluid-dynamic situation in the region of the mantle wedge.