Temporal variations in stable isotopes and synchronous earthquake-related changes in hot springs

Abstract

Abstract Earthquake-related hydrogeochemical changes are considered a possible means of identifying earthquake precursors. This work investigated the time series of hydrogen and oxygen stable isotopes at three hot springs in Kangding with different temperatures, namely, the Erdaoqiao, Longtougou, and Guanding hot springs, located in the Xianshuihe fault zone, one of the most active seismic fault zones in China. The hot springs were observed with a sampling frequency of 3 or 4 days for one year. The results showed that the three hot springs were recharged by meteoric water, and there was a slight water-rock interaction at the Longtougou hot spring. The different isotopic compositions of the three hot springs were related to the recharge and groundwater circulation environment. Temporal anomalies in the stable isotope values at the three hot springs occurred synchronously; these anomalies were closely related to the 2019 Mw 5.8 Changning earthquake, indicating possible earthquake-related changes. Moreover, the amplitudes of stable isotope variations at the three hot springs were closely related to the seismic energy density, and the background isotopic changes were related to the water temperature and flow. These findings reflect the hydrological cycle processes of geothermal water in the Kangding geothermal area on the eastern margin of the Tibetan Plateau. Simultaneously observed temporal variations in hydrogen and oxygen stable isotopes among multiple hot springs may have relevance for distinguishing earthquake precursors.