The materials of measurements of long-wave oscillations obtained from a Tsunami Warning Service recorder in the port of Posyet (2013‒2025) and two autonomous stations in Vityaz Bay (July–October 2009) in Posyet Bay were analyzed. It was revealed that in the spectra of the records in Posyet peaks at periods of about 91, 32, and 18.5 min and at a period of 48 min in Vityaz Bay are significantly distinguished. They were present almost continuously, except for the period from mid-October to mid-November 2024, when intense chaotic variations prevailed in the range of 30–60 min. The intensity of these peaks increased during hazardous marine phenomena, such as storm surges and tsunamis, which suggests a connection with the resonance features of Posyet Bay and their importance in the transformation of the wave field under various weather conditions. Numerical modeling revealed that the complex configuration of the bay makes it difficult to apply traditional seiche classification. Thus, even the low-frequency component with a period of about 91 min, due to the shelf resonance, meets the usual characteristics of such only in the outer part of the bay, up to the foreland that separates the shallow Novgorodskaya and Ekspeditsii bays, in the water area of which its own peaks and nodal lines are distinguished. The mode with a period of 49 min has the character of a single-nodal transverse seiche (with peaks at the Gamov and Suslov peninsulas) only in the part of the outer water area beyond the Reid Pallada Bay. The spatial structure of the eigenmode with a period of about 33 min in the seaward is similar to the two-node longitudinal seiche. Both of these components are characterized by a large number of nodes and nodal lines in the inner basin with small amplitudes of oscillations. The zeroth mode with a period of about 70 min plays an important role in the formation of the wave field, mainly in Reid Pallada Bay, but it is weakly expressed in the area where the level fluctuation recorders are located, which makes it difficult to assess its real role based on the observation data.
Shevchenko et al. (Wed,) studied this question.