关键词: 热水泉, 氢气, 断层土壤气, 气相色谱仪, 痕量氢自动分析仪

Abstract:

Large-scale observation network has been set up in China, including the observations of groundwater dynamics, geothermal water, and geochemical parameters, and long-term observation data has been obtained for underground fluids. Hydrogen observation is considered to be one of the methods that are most likely to make a breakthrough in the aspect of earthquake precursor monitoring and prediction, thus, plays an important role in earthquake monitoring and forecast in China. Many scholars have carried out research on the relationship about hydrogen and earthquake precursors, and proved that abnormal hydrogen concentrations are related to and have certain correlations earthquake activities. The main objects of hydrogen observation in China include the escaping gas from fault soil and the escaping gas from deep wells and hot springs near the fault. Different analytical methods are used for different types of hydrogen, and the main methods include gas chromatograph analysis and digital high-precision hydrogen analyzer analysis. Through years of observation practice, a large number of typical examples have been obtained in China. The relationship between the abnormal hydrogen concentration and the earthquake has a correspondence. The main manifestation is that the hydrogen concentration increases several times or even tens or hundreds of times in a few months or a few days before the earthquake. It is mainly divided into two cases: First, it rises rapidly to several times in a short time before the earthquake. The concentration reaches about hundreds of times the background value in more than ten to a few days immediately before the earthquake, and then the earthquake occurs. The concentration quickly declines and restores the background value after the earthquake. Second, the hydrogen concentration continues to increase in fluctuation, and decreases after reaching the maximum value, then, the earthquake occurs after recovery. This kind of anomaly is short in time, mostly, they are imminent or medium and short-term abnormalities. Therefore, the hydrogen response to the earthquake precursor is an important short-imminent earthquake prediction indicator, and can be used as an important approach to explore the short-impending earthquake prediction.
The hydrogen in the crust mainly comes from biochemical and chemical actions. The hydrogen on the surface layer of the crust is mainly produced by microbial decomposition of organic matter and mineral salts. It is regularly symbiotic with gases such as methane and carbon dioxide. The hydrogen in the crustal fault belts, especially in the active fault zones, also comes from the failure and deformation of rock. The formation mechanism of hydrogen in the crust can be summarized into 3 categories: 1)Under normal circumstances, the hydrogen content is very low, and most of them exist in the pores of the rock and soil layer in a free state, or are adsorbed on the surface of the rock. When the external conditions remain unchanged, the gas is in a balanced state; when the environment changes, especially the underground stress changes, the cracks develop continuously under the action of tectonic stress, resulting in interconnecting each other, and subsequently, the deep hydrogen also changes and emits to the ground surface, including the imminent rupture stage in the earthquake preparation and rock oscillation; 2)The chemical reactions occur between the crushed rock's fine particles and water, generating hydrogen; 3)The temperature gradient causes the hydrogen attached in the crack to escape.
In short, hydrogen is a better method for studying earthquake reflecting ability among the underground fluid observation methods. Representative earthquake cases are obtained from observations of both dissolved hydrogen in the water or soil hydrogen. This observation item plays an important role and has practical significance in the geochemical observation means. In the observation of earthquake underground fluids, hydrogen observations can provide data support for future earthquake risk zoning and earthquake tendency tracking and analysis.

Key words: hot spring, hydrogen, soil gas, gas chromatography, automatic trace-hydrogen analyzer