Soliton-like waves in the coastal zone of the eastern coast of Sakhalin Island

An analysis of a time series of sea level oscillations with a total observation duration of about 14 years was carried out. The aim of the research was to study the possibilities of generating soliton-like waves in the form of wave packets with a soliton envelope. Bottom autonomous wave recorders models ARW-10 to ARW-14K, with one second discretization, were installed in the coastal zone of the southeastern coast of Sakhalin Island. The wave time series were subjected to bandpass filtering in the period range of 15 min to 3 h, revealing nine events in which the amplitudes of anomalous waves exceeded the background level by more than twice. For the selected events, modeling using the time-like form of the Korteweg–de Vries (KdV) equation was performed, showing that the soliton serves as the envelope for the registered wave packets. The possibility of describing such packets using breathers was considered, as each event presented a wave packet rather than a single wave, indicating modulation of the soliton envelope. A possible mechanism for the generation of soliton-like waves was considered, and a criterion for the range of propagation speeds of these waves was proposed, analogous to tsunami waves, as both are long waves. Using the speed range and distances to potential seismic sources of anomalous waves, determined from maps, intervals of seismic events from August 2008 to June 2022 with magnitudes greater than 5, corresponding to the possible arrival of anomalous waves at the coast of Sakhalin Island, were identified. From these waves, the one whose arrival time coincided with the observation time of the soliton-like wave was selected, and it was determined which earthquake could have generated the arriving wave. It was found that four events from the selected ones met the condition of soliton-like waves arriving from seismic sources at the observation point. It was shown that despite the assumptions made in choosing the criterion for the propagation speed of soliton-like waves, the interval of time during which a particular earthquake occurred was determined uniquely, and no other earthquakes fell into it. The obtained result suggests that the generation of soliton-like waves may be associated with seismic sources; however, this issue requires separate detailed studies.