## 3 Sampling and Analytical Methods  
From 28 January to 3 February 2024, a seven-day field campaign was conducted to investigate post-seismic hydrogeochemical changes. A total of 16 hot spring water samples (S1-S16) and two gas samples (G1, G2) were collected from the MDF and its surrounding areas, with G1 corresponding to S1 and G2 to S13. Among them, G1 corresponds to S1, located at the intersection of the Taraz-Fergana Fault (TFF) and MDF, while G2 corresponds to S13, situated solely along the MDF. Due to the emergency nature of the investigation and logistical constraints in this remote region, only two gas samples were obtained. Despite the limited dataset, the selected sites provide valuable spatial contrasts for understanding gas migration behaviors under differing fault conditions. Data for S17 and S18 were obtained from previous study [57]. At each sampling location, three replicate subsamples were gathered for the analysis of major ions and hydrogen and oxygen isotopes (\(\delta\)18O and \(\delta\)D). Before collecting the samples, each bottle was rinsed three times with the sample water. The water was subsequently filtered through a 0.22 \(\upmu\)m filter membrane and transferred into 100 mL polyethylene bottles. These bottles were sealed with parafilm to prevent contamination from the surrounding air. To maintain the stability of trace elements, 1-2 drops of 14M nitric acid were added, adjusting the pH to below 2. Samples were then stored in a refrigerator. The water temperature (T) was measured at a depth of 20 cm using a calibrated Handheld Precision DigitalThermometer PR710A (accuracy \(\pm\)0.1 \({}^{\circ}\)C), after allowing 5 min for thermal equilibration in flowing water. Meanwhile, pH and conductivity were assessed using a Thermo Scientific(tm) Orion Star(tm) A325 multiparameter meter (with an accuracy of 0.01, Thermo Fisher Scientific, Waltham, MA, USA). Continuous monitoring at S13 (144 km from the epicenter of the Wushi \(M\)S7.1 earthquake) (Figure 1) included water sampling every three days. All water samples were transported to the Earthquake Prediction Laboratory of the China Earthquake Administration for hydrogeochemical analysis. Major cations (Mg\({}^{2+}\), Ca\({}^{2+}\), K\({}^{+}\), Na\({}^{+}\)) and anions (SO\({}_{4}\)\({}^{2-}\), Br\({}^{-}\), Cl\({}^{-}\), NO\({}_{3}\)\({}^{-}\)) were analyzed using an ion chromatograph (Thermo Scientific Dionex AQUION IC, Thermo Fisher Scientific, Waltham, MA, USA) equipped with an A540 automatic sampler. The analysis achieved \(\pm\)2% precision, with a detection limit of 0.01 mg/L. HCO\({}_{3}\)\({}^{-}\) and CO\({}_{3}\)\({}^{2-}\) concentrations were measured using a ZDJ-100 potentiometric titrator (Beijing Xianqu Weifeng Technology Development Co., Ltd., Beijing, China) with 0.05 mol/L HCI, employing 0.1% methyl orange and 1% phenolphthalein as indicators, achieving a reproducibility of \(\pm\)2%. Trace elemmrts (Li, B, Al, Ba, Ge, Rb, Cs, V, Be, Mo, Cr, Sr, and Sb) were analyzed using an Agilent 8900 ICP-QQQQ (Agilent Technologies, Santa Clara, CA, USA). The analytical precision, expressed as the relative standard deviation (RSD), was within 5% [58]. Oxygen (\(\delta\)18O) and hydrogen (\(\delta\)D) isotopes were analyzed using a Picarro L2140-I liquid water and vapor isotope analyzer (Picarro Inc., Santa Clara, CA, USA), referenced to Vienna Standard Mean Ocean Water (V-SMOW). National reference standards (GBW04458, 04459, 04460 [59]) were used, with analytical precision of 8D \(<\pm\)0.05% and \(\delta\)18O \(<\pm\)0.015%. \(\delta\)13C in dissolved inorganic carbon (\(\delta\)13C DIC) was analyzed following a closed-system approach. Water samples containing at least 50 \(\upmu\)g of carbon were purged with helium to remove residual CO\({}_{2}\) and then transferred into pre-evacuated, helium-flushed Labco Exetainer tubes (Labco Limited, Lampeter, UK). One milliliter of 85% phosphoric acid was injected into each tube, and the reaction was carried out under sealed conditions to prevent isotopic exchange with atmospheric CO\({}_{2}\)[60].