<p>The Xianshuihe fault zone, an active continental strike-slip system located in the eastern Tibetan Plateau, exhibits intense seismicity and widespread geothermal activity. However, the mechanisms by which hydrochemical changes in geothermal systems respond to earthquakes remain poorly constrained. Here we present a time series dataset of hydrochemical and isotopic parameters (e.g., major ions, trace elements, δ¹⁸O_H2O, δD_H2O, δ¹³C_TDIC, and Δ¹⁴C_TDIC) from five thermal springs located near the epicenters of the 2022 Ms 6.8 Luding earthquake. The stability of most major ions, δ¹⁸O_H2O, and δD_H2O values suggests that post-seismic change is primarily governed by internal aquifer processes. Thermal waters are primarily recharged by meteoric precipitation and affected by minor water–rock interaction. The variation in the δ¹³C_TDIC following the mainshock indicates the input of deep CO₂ into the geothermal system through the opening of a deep fault driven by subsequent stress redistribution. Combining geochemical with geophysical evidence suggests that vigorous deep-sourced CO₂ (C_deep) originates from crustal metamorphic decarbonation, likely associated with the ascending mantle materials and the crustal channel flow driven by the Indo-Eurasian collision. The continuous accumulation of deep CO₂ in the crust generated over-pressurized reservoirs at depths and enhanced the mechanical weakening of faults. Our findings demonstrate the sensitivity of deep carbon release in geothermal systems to seismic activity, highlighting the potential of hydrogeochemical monitoring for earthquake predictability and providing insights into the complex interactions between deep fluids and seismicity in active tectonic settings.</p> Graphical Abstract <p></p>