Alisa Medvedeva

The main motivation of this research is to assess the trends of storm recurrence for the time period from 1979 up to 2020 and to analyze the connection between storminess and large-scale atmospheric circulation indices. This research contains information about the number of storms that occurred in seven Russian Seas, including the Black, Caspian, Barents, Kara, Bering Seas, the Sea of Okhotsk and the Sea of Japan/East Sea. The analysis of wave climate and storm activity is based on the results of wave modeling by WAVEWATCH III with input NCEP/CFSR wind and ice data. The long-term significant wave height (SWH) maximum is 15.5 m in the Sea of Okhotsk and 16.5 m in the Bering Sea. Significant linear basin-wide positive trends in the number of storms were found in the Kara, Caspian, Bering, Okhotsk Seas, and in the Sea of Japan. The weak positive correlation was found only between the number of storms and North Pacific index in the Bering Sea and between the number of storms and Arctic oscillation index in the Barents Sea. For other seas, it is no connections between number of storms and large-scale atmospheric indices, therefore, storm activity in the inner and semi-closed seas is regulated by the local wind and ice conditions, basin orography and bathymetry.

Two powerful earthquakes struck southeastern Turkey on 6 February 2023 with the magnitudes of M_w = 7.8 and M_w = 7.5 in nine hours. In addition, a storm surge caused by the passage of a cyclone over the area coincided with the first earthquake. Field observations showed that the fault planes did not extend to the Mediterranean Sea; however, a weak tsunami was observed on several tide gauges in the northeastern Mediterranean. Historically, there were tsunamis in the Levantine Sea region caused by earthquakes on land within the East Anatolian Fault Zone and the Dead Sea, having a complex cause, i.e., earthquakes and associated landslides. Hence, we studied the origin of the generated waves. We separated and estimated various components of sea level oscillations from 1 to 8 February 2023, using spectral and f-t analyses and sets of narrow-band and high-frequency filters. The earthquake M_w = 7.8 on 6 February 2023 caused a weak tsunami with maximum amplitudes 15‒17 cm in Erdemli and Arsuz. We identified that the increase in sea level oscillations in Arsuz after 7 February was associated with the impact of the cyclone. The maximum amplitude of sea level oscillations, 22 cm, in Arsuz was observed on 7 February and is associated with infragravity waves caused by the influence of storm surge during the passage of the cyclone. In Erdemli, on the contrary, the influence of high-frequency waves of atmospheric origin is significantly lower, i.e., the amplitude of the sea level oscillations after 7 February was less than 10 cm.

The Hunga Tonga volcanic eruption on 15 January 2022 created a tsunami affecting the entire Pacific Ocean. The observed tsunami was found to have a dual mechanism and was caused both by the wave incoming from the source area and by an atmospheric wave propagating with the speed of sound. The tsunami was clearly recorded in the marginal seas of the northwestern Pacific, including the Sea of Japan, the Sea of Okhotsk and the Bering Sea, in particular on the coasts of Kamchatka, the Kuril Islands and the Aleutian Islands. We examined high-resolution records (1-min sampling) of about 50 tide gauges and 15 air pressure stations in these seas for the period of 14-17 January 2022. On the Russian coast, the highest wave with a trough-to-crest wave height of 1.4 m was recorded at Vodopadnaya, on the southeastern Kamchatka Peninsula; on the coasts of the Aleutian Islands the tsunami waves were even higher, up to 2 m. Based on numerical modelling we estimated the arrival time of the gravitational tsunami waves from the source. We revealed that the character of sea level oscillations for most of the stations evidently changed before these waves arrived. A comparative analysis of sea level and atmospheric data indicated that these changes were probably caused by the atmospheric waves generated by the volcanic eruption.

A regional model of tsunami seismic sources in the zone of the Main Caucasian thrust has been developed. The parameters of probable models of seismic sources and their uncertainties were estimated based on the available data on historical earthquakes and active faults of the region. The scenario modeling technique was used for the tsunami zoning of the Caspian Sea coast. The time period covered by the model catalog of earthquakes used to calculate the generation and propagation of tsunamis is about 20 000 years, which is longer than the recurrence periods of the strongest possible earthquakes. The recurrence graphs of the calculated maximum tsunami heights for the entire sea coast were plotted. On their basis, the maximum heights of tsunami waves on the coast were calculated with recurrence periods of 250, 500, 1000 and 5000 years and the corresponding survey maps of the tsunami zoning of the Caspian Sea were created. The algorithm for calculating the tsunami run-up on the coast is improved, taking into account the residual (postseismic) displacements of the bottom and land relief. Estimates of tsunami hazard for the coast near the city of Kaspiysk were carried out: within the framework of the deterministic approach, the maximum wave heights and run-up distance were calculated. It is shown that the deterministic approach slightly overestimates the maximum heights of tsunami waves with certain return periods. It is shown that changes in the mean sea level can affect the features of the propagation of tsunami waves in the Caspian Sea. Thus, at an average sea level of -25-26 m, the Kara-Bogaz-Gol Bay is linked with the entire sea through a narrow strait. It leads to the propagation of tsunami waves into the water area of the bay and a decrease in wave height on the eastern coast of the sea. When the mean sea level decreases below -27 m, the positive depths in the strait disappear and water exchange through the strait stops, and the wave height in this part of the sea increases.