Expanding Seismicity and Paragenetic Variations in Groundwater Composition in the Baikal Rift System in 2020-2025: Current State Assessment of the Earth's Crust

We present monitoring results of U-components, Li, Na, and Si in groundwater from the structural junction of the South Baikal Basin and Tunka Valley. The former is the center of the Baikal Rift System (BRS) that is extended; the latter is its western part that is affected by extension combined with compression. On the one hand, we trace sharp changes in hydrogeochemical parameters in 2020– 2025 that correspond to structural reorganizations of the earth's crust; on the other hand, we use the structural reorganizations to determine spatial-temporal features of strong earthquakes. We compare the identified hydrogeochemical reorganizations of the groundwater reservoir and timing of strong earthquakes of the Baikal-Khubsugul seismic reactivation in the center and west of the BRS and more expanded reactivation from Northern Baikal to Hangay in its northeast, center, and west. From a series of comparative hydrogeochemical and seismic data, we assess the state of the earth's crust of the BRS in May-June 2025 and infer that a current seismogenic deformation regime of the North Baikal-Hangay reactivation displays remote moderate-strength earthquakes at the ends of the Khentei-Udokan hot corner zone of the Japan-Baikal geodynamic corridor with simultaneous advancement to the west, along the Khubsugul-Darkhat-Busingol rift segment of the basins–pendants.