Fault-controlled hydrogeochemical spatial evolution revealed by machine learning around the 2010 Ms 7.1 Yushu earthquake zone

Study Region: The Ganzi-Yushu fault zone (GYFZ) is an active strike-slip fault on the eastern Tibetan Plateau, separating the Bayan Har and Qiangtang blocks. Study Focus: Active strike-slip faults can act as barriers and conduits for groundwater, making them important settings for understanding how seismic deformation redistributes meteoric recharge and deep volatiles. In the GYFZ, along-strike fault coupling, the 2010 Yushu rupture, and heterogeneous lithologies require clarification of how fault architecture controls groundwater circulation and hydrochemical differentiation. New Hydrological Insights for the Region: Hydrochemical, water-isotope, gas-isotope, and unsupervised machine-learning evidence (Principal Component Analysis (PCA), K-means clustering, and Uniform Manifold Approximation and Projection (UMAP)) from 31 water samples and 9 gas-sampling sites shows the GYFZ is compartmentalized. Stable isotopes indicate meteoric recharge, but circulation is partitioned by mechanical state. Highly coupled locked sectors preserve dilute meteoric Cluster 2 waters and limit vertical exchange with deep fluids. Ruptured and coupling-transition domains provide conduits for deeper, warmer Cluster 1 fluids, producing SiO 2 , Na + , Cl - , and HCO 3 - enrichment and variable volatile input (CO 2 = 1.02–99.04%; Rc = 0.10–0.51 Ra). Cluster 3, represented by GQNY, records a local sulfate-rich flow path through evaporitic and carbonate lithologies; its SO 4 2- enrichment reflects mineral availability and hydrological connectivity rather than CO 2 -driven acidity. Thus, fault coupling determines conduit-barrier behaviour, whereas lithology controls the reaction fingerprint, explaining localized volatile-bearing anomalies along the fault.