Hot spring water observations and its anomalies before the Lushan M_S7.0 earthquake in the western Sichuan region

On the basis of field survey of fluid observation sites near the epicenter of 2013 Lushan M_S7.0 earthquake, hot spring temperature data observed at the sites with better observation environment and little human disturbance in the western Sichuan Province were selected to perform retrospective analysis. The results showed that different degrees of water temperature anomalies were observed at Longtougou and Erdaoqiao sites in Kangding region, Longpugou site in Daofu county, Maoya site in Litang county, Gonghe site in Luding county before the Lushan M_S7.0 earthquake. It was mainly showed that the mid-term anomalies about two years of time scale were observed at Maoya and Longpugou hot spring sites far from the epicenter of Lushan earthquake; while the short-term anomalies within three months preceding the earthquake were observed at Longtougou and Erdaoqiao hot spring sites which were close to the earthquake epicenter. By the spring water hydrochemistry and δD-δ¹⁸O stable isotopes analysis, it was suggested that these hot spring water have deep circulation characteristics, so the temperature changes of hot spring water can sensitively reflect deep crustal information in respect of geothermal and tectonic changes, which was the possible cause for the anomalies observed at the hot spring water preceding the Lushan earthquake. It was significant for the regional earthquake prediction research to strengthen observation of these hot spring sites.