Studying the hydrogeochemical characteristics of hot springs provides essential geochemical information for monitoring earthquake precursors and understanding the relationship between fluids, fractures, and earthquakes. This paper investigates the hydrogeochemical characteristics of hot springs along the Tingri–Nyima Rift (TNR) in southern Tibet, a seismically active zone at the collision front of the Indian and Asian-European plates. The major elements, hydrogen, and oxygen isotopes of seven thermal springs were analyzed from July 2019 to September 2021. The findings indicate that Mount Everest’s meteoric water, which has a recharge elevation of roughly 7.5–8.4 km, is the main source of recharge for the hot springs. The water samples have two main hydrochemical types: HCO3-Na and Cl-Na. The temperature of the geothermal reservoir is between 46.5 and 225.4 °C, while the circulation depth is between 1.2 and 5.0 km based on silica-enthalpy mixing models and traditional geothermometers. Furthermore, continuous measurements of major anions and cations at the Yundong Spring (T06) near Mount Everest reveal short-term (8 days) seismic precursor anomalies of hydrochemical compositions before an ML4.7 earthquake 64.36 km away from T06. Our study suggests that seismicity in the northern section of the TNR is controlled by both hydrothermal activity and tectonic activity, while seismicity in the southern section is mainly influenced by tectonic activity. In addition to magnitude and distance from the epicenter, geological forces from deep, large fissures also affect how hot springs react to seismic occurrences. A fluid circulation model is established in order to explain the process of groundwater circulation migration. The continuous hydrochemical monitoring of hot springs near Everest is critical for studying the coupling between hot springs, fractures, and earthquakes, as well as monitoring information on earthquake precursory anomalies near Everest.
The geosynthetic clay liner (GCL) is a kind of waterproofing material used widely in engineering. The waterproof mechanism is understood in terms of bentonite particles becoming water‐obstruct colloid layers after they sorb water and swell. The swell pressure stress, however, has not been determined directly till now. In our experiment, swell pressure stress of the GCL under saturated water‐sorbing condition was measured directly using a custom‐made instrument. The results show that (1) the instrument designed by the authors performs satisfactorily and the test results are reproducible; and (2) the trend line of swell pressure stress variation with time can be divided into three segments. The first segment is characterized by a quick increase of the swell force in the first 0–50 hours. The swell pressure stress increases by 7.00times10−4‐1.00times10−3 MPa/h. The second segment shows a slow increase of the swell pressure stress from the 50th to 1730th hour. The swell force increases by 7.54times10−6‐2.02times10−5MPa/h. The third segment is characterized by a little variation in swell pressure stress after 1730 hours. In this segment, the average value of the swell pressure stress measurements is 0.0719 MPa and the maximum value is 0.0729 MPa. It is suggested that the swell pressure stress is mainly raised by water entering pores among montmorillonite particles and interstitial layers in individual montmorillonite crystals, leading to an increase of volume.
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