Mercury signals of groundwater of the Kultuk area during the preparation and implementation of the Baikal-Khubsugul seismic reactivation in 2020–2021

From 5-year monitoring of groundwater in the Kultuk area, long-period (about 2.5 years) and short-period (months) variations in mercury concentration have been established. Long-period variations are associated with the preparation and implementation of the Baikal-Khubsugul seismic reactivation; short-period ones – directly with earthquakes. Mercury concentrations was low in groundwater in 2015, when seismogenic deformations developed in a state of crustal compression, and generally increased to 2020–2021, when seismogenic deformations occurred under extention. The course of the seismic process was reflected in a successive change in mercury/redox potential rеlationship in groundwater. It is proposed that the anomalous behavior of mercury during seismic activity resulted in increasing its concentration in the sedimentary layers of the second half of the 18th century through the present.