Abstract: Hydrogeochemical anomalies in hot spring water can reveal short-term precursory anomalies before earthquakes, yet there remains divergent understanding the significance of the anomalies in different chemical components. This study presents a two-year continuous observation of major elements and isotopes in three hot springs located within 150 kilometers of the epicenter of the Longyang M_S5.2 earthquake that occurred on May 2^nd, 2023.The results reveal synchronous anomalies(δ18O、 δD、 SO^2-₄、 Cl^-)around three months (93~120 d) before the earthquake at the Eryuanniujie hot spring, characterized by deep water circulation and intense water-rock interactions. The Jiancao hot spring exhibited anomalies in volatile components (Cl^-) 112 days before the earthquake, likely influenced by deep-seated gases. Conversely, anomalies in major ions appeared approximately one month (36~43 d) before the earthquake at the Lianchangping hot spring, where shallow water circulation and pronounced mineral dissolution effects are observed. The hydrological and geochemical precursory anomalies in these three hot springs suggest that chlorine, as a volatile element, can carry more profound information, making it an advantageous indicator of short-term earthquake precursors. The simultaneous anomalies in multiple chemical components provide clearer earthquake indications. The timing of anomalies correlates with the depth of water circulation: anomalies in deeper circulating hot spring water appeared approximately three months before the earthquake, while those in shallower circulating hot springs occurred about one month prior. Comparative analysis of the post-seismic trends in the Eryuan Niujie hot spring following the 21^st May, 2021 Yangbi M_S6.4 earthquake indicates that hot springs within the same fault system as moderate earthquakes undergo disrupted water circulation and re-established a new equilibrium after them. Therefore, the background values of hot spring water following moderate earthquakes must be re-evaluated in the context of the specific tectonic settings.

Key words: Hydrogeochemistry, Hot spring, Earthquake short-term precursor anomalies, The 2023 Longyang M_S5.2 earthquake, Hydrogen and oxygen isotopes