| A high-fidelity record covering nearly 40 years of water-dissolved radon,water temperature and discharge rate from the hot spring site of Banglazhang,Southwestern China,combined with regional rainfall,air pressure,earthquake and solar activity,were presented to study the relationship between radon,water temperature,discharge rate and their influence factors,as well as the multi-year periodicities.Meanwhile,the characteristics and mechanism of radon,water temperature and discharge rate changes in the hot spring water were analyzed.Furthermore,the earthquake prediction efficiency of water radon,water temperature and discharge rate of the hot spring water was statistically tested.It is of great scientific significance to understand the relationship between hot spring fluid and seismic activity,especially to explore the precursor of hot spring fluid.The time series of water radon,water temperature and discharge rate were characterized by a quasi-decadal?8-11 years?periodicity and quasi-synchronous change characteristics.The water radon was negatively correlated with water temperature.The water temperature was positively correlated with discharge rate.Variations in water radon,water temperature,discharge rate and ancillary observational data were studied using continuous Wavelet Power Spectrum?WPS?,Wavelet Coherence?WTC?,and Partial Wavelet Coherence?PWC?.The results show that the long-period water radon was characterized by a quasi-decadal?8-11 years?cycle,matching well with the concurrent periodicity in water temperature,spring discharge rates and GCR.WTCs and PWCs of radon,discharge rate and water temperature suggest that water temperature variations explain most of the coherent variability of radon and the discharge rate.We tentatively conclude that radon variations were mainly explained by variations in water temperature and spring discharge,which were modified and modulated by earthquakes and quasi-decadal variations of an unidentified process.According to the coseismic water radon,temperature and discharge rate changes in the hot spring field of Balazhang following the 1976 Longling MW7.0,the 1996Lijiang MW 6.6 and the 2004 MW 9.1 earthquakes.Coseismic static strain model,sustained and temporary permeability change model,and regional recharge decrease model were used to constrain the permeability change and the mechanism of coseismic hydrological changes.Meanwhile,combined with end-member mixing model,the hydrological changes caused by earthquakes are physically explained.The results show that coseismic static strain model can not explain the hydrological changes caused by earthquakes in the Banglazhang hot spring site.The earthquake-induced permeability decrease in the fault zone reduced the recharge from deep hot water,which may be the mechanism that explains the coseismic discharge and temperature responses.The changes in the hot spring response reflect the dynamic changes in the hydrothermal system;in the future,earthquake-induced permeability decrease should be considered when discussing controls on permeability.After analyzing the influencing factors of water radon,temperature and discharge in the Banglazhang hot spring site,the method of superposed epoch analysis?SEA?and Molchan error diagram were used to test statistically the significance of earthquake precursor.The results of SEA indicate that anomaly frequency of the water radon and temperature was above average value at the range of80 days and one month,and anomaly frequency increase gradually within one month.The results of Molchan error diagram indicate that water radon and temperature have certain short-term earthquake prediction significance to the earthquakes of corresponding strain above 10-8.The probability gain was between 2 and 4,and water radon and temperature has better earthquake predictive effect than discharge rate. |
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