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The 2011 M w 9.0 Tohoku earthquake and the 2012 M w 8.6 and 2016 M w 7.8 Sumatra earthquakes caused water level oscillations in Lake Baikal which were recorded by a water pressure tensor transducer with high sampling rate. Periods of water oscillations were about 100 s, and maximum peak-to-peak amplitudes were as large as 0.15 m for the 2011 Tohoku earthquake and 0.24 m for the 2012 Sumatra earthquake, although the Tohoku earthquake was closer and stronger. The difference in the amplitude of the level oscillations for these earthquakes was probably caused by their focal mechanisms, namely thrust and strike-slip, as well as the direction of the wave propagation. CTD (conductivity-temperature-depth) measurements conducted after these earthquakes at the regularly tested stations showed a temperature increase in the near-bottom water layer after the Tohoku earthquake in March 2011, and a decrease in temperature and electrical conductivity after the Sumatra earthquake in March 2016. These observations cannot be explained by the known processes of deep water renewal, so based on the gas hydrate presence in the Baikal sediments we assume that seismic wave passing could change permeability in the sedimentary layer (at least for the 2011 Tohoku case study) and promote methane flux from the base of the hydrate stability zone and formation of gas hydrates with heat release. As to the 2016 Sumatra study case, we suppose to explain it by gas hydrate dissociation in the subsurface sediments. We present rough estimates of the volume of the formed/dissociated gas hydrates. [ABSTRACT FROM AUTHOR]

In September 2008, freshening of near-bottom water and an increase in concentration of suspended particles were observed in the western part of southern Lake Baikal. The reduction in the content of total dissolved solids was about 0.4-0.7 mg/kg (0.7 %), and average suspended particle concentration increased strongly to 6-9 mg/l, the background value being 0.2 mg/l. The spatial distribution of these waters was virtually identical to the focal area of the M6.2 Kultuk earthquake that occurred on 27 August 2008. It is suggested that there was a causal relationship between these two phenomena. Freshening of a significant amount (about 20 km) of near-bottom waters was plausibly caused by an input of poorly mineralized pore waters from bottom sediments as a result of dissociation of methane gas hydrates suspected to occur in the area. The energy radiated by the earthquake source was four orders of magnitude smaller than that needed to explain the observed freshening of near-bottom waters. This points to other mechanisms leading to seismic-induced sediment failure and possible subsequent hydrate dissociation in the case of the Kultuk earthquake. [ABSTRACT FROM AUTHOR]