Tsunami Waves off the Southeastern Coast of Sakhalin Island Caused by the Eruption of the Hunga–Tonga–Hunga–Ha’apai Volcano on January 15, 2022 According to Observations by Bottom Devices of Waves

The observation of waves (sea level oscillations) in the coastal water area of the southeastern coast of Sakhalin Island was carried out from November 2021 to May 2022 using bottom-mounted high-precision ARW 14 K devices with one second discreteness. The analysis of the obtained time series revealed the presence of anomalous waves in the range of tsunami waves in January 2022. It is shown that the waves detected on January 15, 2022 with periods of 15 min–4 h, significantly standing out above the background, are associated with volcanic tsunami waves. Spectral analysis of the time series showed that the maximum in the spectra of sea level oscillations found after the volcanic eruption is close to the period of the first mode of the shelf seiche. This indicates that incoming tsunami waves excite shelf seiches in the coastal zone and contribute to the generation of longshore and transverse seiches into Mordvinov Bay. Time series analysis made it possible to establish that the spectral density of sea level oscillations for the time interval of the beginning of the eruption of the Hunga–Tonga–Hunga–Ha’apai volcano from December 21, 2021 to January 11, 2022 significantly differs from the spectral density for the time of the Plinian volcanic eruption. An analysis of the statistical characteristics of sea level oscillations performed on two-day series in the range of periods 1 min–4 h for background waves and tsunamis showed an increase in the rms by 3.5 times for a time series containing tsunami waves. It has been established that for background time series containing tsunami waves, the coefficients of asymmetry and kurtosis differ little from ‘‘Gaussia’’ values. This indicates that the arrival of tsunami waves from distant sources does not significantly disrupt the stationarity of the wave field in the observation area.