Coseismic temporal variations of thermophilic element Si in groundwaters from the SW coast of Lake Baikal in 2012–2022

The results of monitoring concentrations of the thermophilic element Si in fresh subthermal and cold groundwaters from the Kultuk polygon with a temperature range at the output from ca. 0 to 20 °C are presented. A stepwise zonal increase in the Si concentration is recognized in groundwaters of the polygon centered at station 40. In this center of the Kultuk hydrothermal reservoir, the minimum temperature of 25 °С on September 17, 2014 (before the earthquakes of 2014–2015) and the maximum temperature of 60 °С on January 23, 2021 (11 days after the strongest Khubsugul earthquake Mw=6.8) is obtained using the chalcedony geothermometer. It is proposed that groundwater came from the deep Kultuk reservoir with elevated temperature during the strong Kultuk seismic reactivation (August 27, 2008 – January 04, 2011) and changed to those with a lower temperature during the weak Tolbazikha one (June 24, 2011 – October 11, 2012) reaching a temperature minimum by 2014. Then the inflow of groundwaters with elevated temperature was revived again during the preparation and implementation of the Baikal-Khubsugul seismic reactivation that was marked by strong earthquakes in 2020–2022.