Pure Appl. Geophys. Ó 2018 Springer International Publishing AG, part of Springer Nature https://doi.org/10.1007/s00024-018-1885-y Pure and Applied Geophysics Hydrogeological and Geochemical Observations for Earthquake Prediction Research in China: A Brief Overview 1 2 2 1 2 2 3 BO WANG, YAOWEI LIU, XIAOLONG SUN, YUCHUAN MA, LEI ZHANG, HONGWEI REN, and ZHEN FANG Abstract—Hydrological and geochemical changes have been a major threat to lives and properties in almost all of studied extensively in China for the purpose of earthquake pre- the Chinese territory (Huang et al. 2017). In addition diction since 1966. This paper gives a brief overview of the findings, which have been reported mainly in Chinese so far. to the exploration of scientific problems and accu- Parameters studied include water level; water temperature; and mulating research data, China also has to carry out radon, hydrogen and mercury concentrations. Significant changes earthquake prediction, which is significantly different have been observed before some large or even intermediate-sized earthquakes, among many cases that did not show any such from other countries. China has been conducting changes. Background noise caused by other environmental vari- systematic research on the relationship between ables and possible mechanisms for the pre-earthquake anomalies earthquakes and groundwater after the Xingtai Ms 6.8 are discussed. Due to the complexity of earthquake prediction, much more monitoring efforts as well as sophisticated analytic and and Ms 7.2 earthquakes of Hebei Province in 1966. synthetic efforts are needed in the future. According to the Earthquake Cases in China from 1966 to 2012, there were about 1162 underground Key words: Earthquake prediction, water level, water tem- fluid anomalies before 170 earthquakes (Sun et al. perature, radon, hydrogen. 2016a, b). China has built a systematic monitoring network of groundwater for earthquake prediction in the past 1. Introduction 50 years. It contains hydrogeochemical observation stations (Rn, H2, He, Hg, ion composition, etc.), groundwater observation stations (water level, flux) Scientists have found that hydrogeological and and geothermal observation stations (water tempera- geochemical changes can be observed in wells or ture, ground temperature). Up to now, more than 684 springs before earthquakes (Hauksson 1981; King observation stations have been set up in almost all 1980, 1984; King et al. 2006; Freund 1985; Roeloffs 1988; Kissin and Grinevsky 1990; Toutain and Bau- provinces of China, with a total of 1522 observation items, including 486 water level observations, 465 bron 1999; Cicerone et al. 2009; Ingebritsen and Manga 2014). China has conducted numerous water temperature observations, 219 radon observa- tions, 15 hydrogen observations of faults, 73 mercury researches on possible precursory anomalies and observations and 264 other observations (Fig. 1). earthquake prediction using hydrogeological and The purpose of this paper is to illustrate the geochemical observations for 50 years. research process of the relationship between China is one of the most seismically active groundwater and earthquakes in China in the past countries in the world. Destructive earthquakes pose decades, summarize the successful experience and inadequacy in the study, and list some aspects that should be studied in the future. It is also hoped that 1 China Earthquake Networks Center, Beijing 100045, international experts in this field would provide good China. suggestions on the research of earthquake prediction 2 Key Laboratory of Crustal Dynamics, Institute of Crustal in China. Dynamics, China Earthquake Administration, Beijing 100085, China. E-mail: [email protected] 3 Anhui Earthquake Administration, Hefei 230031, China. B. Wang et al. Pure Appl. Geophys. Figure 1 The distribution of subsurface fluid observation stations for earthquake prediction. a Water level, b water temperature, c radon, d mercury, e hydrogen, f others 2. Hydrogeological Observations phenomena are also observed in groundwater wells in China (Cai 1980; Li et al. 1990; Zhu et al. 1997). To The analysis of the hydrogeological changes in remove the environmental variables that influence wells or springs is an important method in earthquake underground water level observations, scientists have prediction research, which aims at capturing crustal used a variety of different data processing methods, strain information before the occurrence of earth- such as regression analysis, wavelet analysis method, quakes. The correlation between the change in spectrum analysis and harmonic analysis, which have groundwater and crustal strain has been a focus of been widely used in the analysis of water level data scientific research in recent years. (Tian and Gu 1985; Zhang et al. 1986a, b, 1989b, c, d; Che et al. 1990; Yu et al. 1990;Du1991; Zhang et al. 1997; Yan et al. 2007; Yan 2008; Lai 2014). In 2.1. Water Level addition, some scholars have found that the earth tide Water level observation is superior in number to characteristics of water level in wells always changed other items in the underground fluid monitoring before earthquakes. For example, Shi and Wang network center of China. Water level observation (2013) calculated the tidal factors and phase lags of instruments have gone through many stages, and now four selected wells and found that the tidal factors of LN-3(A) digital instrument, designed by the Institute the four wells were in a rapidly changing stage before of Earthquake Science of China Earthquake Admin- the Wenchuan 8.0 earthquake in 2008, but the phase istration with a resolution of 1 mm, has been widely lag and the tidal residual phase were in a rapidly used for water level measurement in the affiliated declining stage, which is a good reflection of the stress departments of China Earthquake Administration. in the well aquifer. The response of water level to the atmospheric Classification and analysis on the water level pressure is prevalent: 54% of the wells have obvious changes caused by big earthquakes have been carried air pressure effect (Che et al. 2006). The tidal out in recent years (Yan and Huang 2009). A great Hydrogeological and Geochemical Observations for Earthquake Prediction Research… deal of research has also been made on the variation annual variation. There are also a lot of researches on of permeability coefficient of aquifer caused by the spatial and temporal characteristics between the seismic waves and the role of dynamic stress and abnormal changes of groundwater level and seismic static stress in the change of groundwater level (Liu activities (Liu et al. 1999; Cao et al. 2002; Yang et al. et al. 2011; Lai et al. 2011; Shi et al. 2013; Shi and 2009). Wang 2015). Besides, some researchers have studied Due to the block structure of China mainland, the influence on future seismicity, by analyzing the researches have been carried out on the changes of changes in groundwater caused by big earthquakes groundwater level related to typical blocks, seismic and claim that the concentration area of coseismic zones or large earthquakes. For example, Liu et al. response of water level is always the area where (2002) analyzed the short-term anomalies of ground- earthquakes are prone to occur in the future (Li 1995; water in the Sichuan–Yunnan region and summed up Huang et al. 2000; Wang 2000). the temporal characteristics and spatial distribution of The sharp rise or fall in water level to the the precursory phenomena. Wang (2004) analyzed exclusion of other environmental variables is gener- the dynamic anomalies of the groundwater in the ally considered to be a possible short-term precursory northern Tianshan Mountain before the six M [ 7 anomaly of earthquake. It may appear as a frequent earthquakes in Xinjiang and neighbor areas since step-like change; for example, Cao and Zhang (1999) 1980 and found the short-term pre-earthquake analyzed and proved that the frequent step-like changes of groundwater level before three earth- changes in Wanquan well have a good correlation quakes, with a prominent coseismic and post-seismic with the nearby regional seismic activities (Fig. 2); it responses. Before the Ludian M 6.5 earthquake of may also appear as a rising trend. For example, the 2014, the long-term and medium-term anomalies of water level of Fengzhen well suddenly rose 40 mm, groundwater were mainly in the range of 62 days before the Zhangbei Ms 6.2 earthquake on 300–500 km from the epicenter, while the short-term January 10, 1998, and then continued to rise by anomalies were concentrated within 100 km from the 60 mm until the earthquake occurred (Ding and Ha epicenter (Liu et al. 2015). 2012). In addition to the short-term anomalies, water Groundwater dynamics is closely related to the level observations also show a monthly variation and geological environment and tectonic background and (a) (b) 100 80 60 40 20 0 Number of step-like changes/month 7.0 6.0 5.0 4.0 3.0 1982 1984 1986 1988 1990 1992 1994 1996 1998 Time/year Figure 2 a Number of step-like changes of groundwater level in Wanquan well and its relationship with regional seismic activities [after Cao and Zhang (1999)]; b the location of earthquake epicenter and Wanquan station B. Wang et al. Pure Appl. Geophys. also affected by meteorological factors and human groundwater temperature, such as rainfall, ground- activities. In the study of precursory observation, the water exploitation and instrument calibration. So, the specific causes of water level changes in observation extraction of such factors is the basis for a better wells should be analyzed in combination with the understanding of the earthquake precursor using structural location and geographical environment of groundwater temperature. the wells, so as to determine whether they are Due to the low thermal conductivity of rocks, it precursory anomalies associated with crustal takes a long time to reach the earth’s surface for the activities. deep water temperature changes in the crust.