Water

Research

25 pages, 4528 KiB

Open AccessArticle

Hydrochemical Characteristics of Hot Springs in the Intersection of the Red River Fault Zone and the Xiaojiang Fault Zone, Southwest Tibet Plateau

by Zirui Li, Xiaocheng Zhou, Qiulong Xu, Yucong Yan, Miao He, Jingchao Li, Jinyuan Dong, Jiao Tian, Fenghe Ding, Ying Li, Chongzhi Ma, Xiaotao Wang and Zhixin Luo

Water 2022, 14(16), 2525; https://doi.org/10.3390/w14162525 - 17 Aug 2022

Cited by 6 | Viewed by 2427

Abstract

The coupling relationship between regional seismic activity and the hydrogeochemical field provides an important theoretical basis for regional earthquake precursor exploration. The intersection area of the Red River fault zone (RRF) and the Xiaojiang fault zone (XJF) in southeast Yunnan province has become [...] Read more.

The coupling relationship between regional seismic activity and the hydrogeochemical field provides an important theoretical basis for regional earthquake precursor exploration. The intersection area of the Red River fault zone (RRF) and the Xiaojiang fault zone (XJF) in southeast Yunnan province has become the focus area of earthquake monitoring and prediction because of its special tectonic position in China. There were 20 hot springs that were sampled and analyzed in the laboratory for major elements, including trace elements, silica, stable isotopes (δ¹⁸O and δD), and strontium isotopes, from the years 2015 to 2019. (1) The meteoric water is the main source of recharge for thermal springs in the study area, and recharged elevations ranged from 1.1 to 2 km; (2) the geothermometer method was used to estimate the region of thermal storage temperature, and its temperature ranged between 64.3 to 162.7 °C, whereas the circulation depth ranged from 1.1 to 7.2 km. Hydrochemical types were mainly controlled by aquifer lithology, in which sodium bicarbonate and sulphuric acid water gathered mainly in the RRF, while calcium bicarbonate water gathered mainly in the XJF. According to the silicon–enthalpy equation method, the temperature range and cold water mixing ratio were 97–268 °C and 61–97%, respectively; (3) the circulation depth of the RRF was deeper than that of the XJF, and it was mainly concentrated in the second segment and the fourth segment on the RRF. Most of the hot spring water was immature with a weak water–rock reaction; (4) the hot water intersections of RRF and XJF were obviously controlled by the fault and the cutting depth of granite; (5) the relationship discussed between geothermal anomaly and earthquake activity had a good correspondence with regional seismicity. The intensity of the reaction between underground hot water and the surrounding rock may lead to the change of pore pressure, and the weakening effect of groundwater on fracture may change accordingly, followed by the change in the adjustment of tectonic stress. Eventually, the difference in seismic activity was shown, implying that deep fluid has an important control action on the regional seismicity. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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32 pages, 41071 KiB

Open AccessArticle

Hydrogeochemical and Isotopic Characteristics of the Hot Springs in the Litang Fault Zone, Southeast Qinghai–Tibet Plateau

by Rui Zhou, Xiaocheng Zhou, Ying Li, Miao He, Jingchao Li, Jinyuan Dong, Jiao Tian, Kaiyue Li, Yucong Yan, Shupei Ouyang, Fengli Liu and Zhixin Luo

Water 2022, 14(9), 1496; https://doi.org/10.3390/w14091496 - 6 May 2022

Cited by 18 | Viewed by 3888

Abstract

Based on the observation of the geochemical characteristics of 19 hot springs in the Litang Fault Zone (LFZ) from 2010 to 2019, the major elements, trace elements, and stable isotopes were investigated, and a conceptual model of ground fluid circulation in the LFZ [...] Read more.

Based on the observation of the geochemical characteristics of 19 hot springs in the Litang Fault Zone (LFZ) from 2010 to 2019, the major elements, trace elements, and stable isotopes were investigated, and a conceptual model of ground fluid circulation in the LFZ was established. The main hydrochemical type of hot spring water samples is HCO₃⁻-Na⁺. The δ²H values range from −157.6‰ to −123.4‰ and δ¹⁸O values range from −24.5‰ to −15.4‰. The hot spring water in the Litang fault zone is mainly recharged by infiltrating precipitation, with a recharge elevation of 4062~6018 m. Hydrochemical types of Litang hot springs are mainly controlled by the circulation of groundwater in a deep fault system, and are related to the rock lithology of thermal reservoir and water–rock reaction areas. Hot springs in the Litang fault zone attribute to three different heat sources, belonging to three geothermal systems. The flow direction of groundwater in the LFZ is roughly from northwest to southeast along the Litang fault. The deeper the circulation depth of hot spring water on the fault, the higher the thermal reservoir temperature and the stronger the seismic activity of the segment, which is closely related to the increase in pore fluid pressure, rock weakening, and deep fluid upwelling. This study is helpful for further study on regional hydrogeological environments and provides a scientific basis for revealing geothermal fluid movement in fault zones. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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23 pages, 21988 KiB

Open AccessFeature PaperArticle

Identification of Groundwater Radon Precursory Anomalies by Critical Slowing down Theory: A Case Study in Yunnan Region, Southwest China

by Zhiyuan Qiao, Guangcai Wang, Hong Fu and Xiaojing Hu

Water 2022, 14(4), 541; https://doi.org/10.3390/w14040541 - 11 Feb 2022

Cited by 9 | Viewed by 2548

Abstract

In this study, we use the critical slowing down (CSD) theory to identify the precursory anomalies of groundwater radon based on the 1000-day continuous data from 8 monitoring stations in Yunnan Province, China during the seismically active period of 1993–1996. The low-frequency and [...] Read more.

In this study, we use the critical slowing down (CSD) theory to identify the precursory anomalies of groundwater radon based on the 1000-day continuous data from 8 monitoring stations in Yunnan Province, China during the seismically active period of 1993–1996. The low-frequency and high-frequency information were extracted from raw groundwater radon data to calculate their one-step lag autocorrelation (AR-1) and variance, respectively, in order to identify the precursory anomalies. The results show that the anomaly characteristics can be divided into three categories: sudden jump anomalies, persistent anomalies, and fluctuation anomalies. The highest average seismic recognition rate is 72.78%, based on the high-frequency information’s autocorrelation, while the lowest is 45.08%, based on the low-frequency information’s variance. The crustal activity and the change in hydrogeological conditions are possibly the main factors influencing groundwater radon anomalies in the selected period in the study area. There is a positive correlation between the anomaly occurrence time and epicentral distance when epicentral distance is less than 300 km, which may be related to the seismogenic modes and hydrogeological conditions. This study provides a reference for identifying groundwater radon anomalies before earthquakes by mathematical methods. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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16 pages, 3656 KiB

Open AccessFeature PaperArticle

Long-Lasting Boiling-Wells: Geochemical Windows into the Tectonic Activity of the Maodong Fault (China)

by Lin Liu, Yuehua Jiang, Xun Zhou, Yun Li, Quanping Zhou, Jingwen Su, Junyuan Jia, Guoqiang Yang and Yang Jin

Water 2022, 14(3), 427; https://doi.org/10.3390/w14030427 - 29 Jan 2022

Viewed by 2349

Abstract

The Maodong Fault (China) was mainly active during the Late Pleistocene. However, in the past century, numerous destructive earthquakes have occurred along the fault zone, indicating its continuing activity. Therefore, refined monitoring of the tectonic activity along the fault is required. Boiling-Wells located [...] Read more.

The Maodong Fault (China) was mainly active during the Late Pleistocene. However, in the past century, numerous destructive earthquakes have occurred along the fault zone, indicating its continuing activity. Therefore, refined monitoring of the tectonic activity along the fault is required. Boiling-Wells located in the Maodong Fault Zone were selected for this purpose. The parameters, including the rare earth elements (REE) and gas components, such as CO₂, Rn, and Total Volatile Organic Compounds (TVOC), in the wells were analyzed. By combining field observations with the analytical data, we constrained the relationships between the anomalies of the hydrochemical composition and the gas composition in the Boiling-Wells and the Maodong Fault: (1) CO₂ and TVOC in the Boiling-Wells originated from Cenozoic magmatism and associated intrusive rocks. High concentrations of Rn are closely linked to tectonic activities of the Maodong Fault. CO₂, TVOC, and Rn are all transported to the Boiling-Wells along the Maodong Fault, with CO₂ acting as a carrier gas for Rn. (2) REE in the Boiling-Wells was mainly sourced from CO₂ fluids that originated from deep-seated Cenozoic magmas and intrusive rocks. The concentrations of the REE and their distribution patterns were controlled by the input of CO₂ fluids and by epigenetic processes. (3) The abnormally high contents of Ca²⁺, HCO₃⁻, Pb²⁺, and Al³⁺ in the Boiling-Wells are attributed to the migration of externally-derived (deep) CO₂ fluids through the Maodong Fault. (4) The anomalies of the gaseous (Rn, CO₂, and TVOC) and hydrochemical components (Ca²⁺, HCO₃⁻, Pb²⁺, Al³⁺, ∑REE, and REE patterns) in the Boiling-Wells are closely related to the tectonic activity of the Maodong Fault. Therefore, the long-lasting Boiling-Wells provide an excellent geochemical window into the evolution of the Maodong Fault. Our study documents that the contents and variations of specific hydrochemical and gaseous components of Boiling-Wells are well-suited geochemical tracers to identify and characterize the tectonic activity of the Maodong Fault. This method is also applicable for the monitoring of tectonic activities of major faults zones with comparable preconditions worldwide. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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20 pages, 8636 KiB

Open AccessFeature PaperArticle

Changes in Fault Slip Potential Due to Water Injection in the Rongcheng Deep Geothermal Reservoir, Xiong’an New Area, North China

by Siyu Zhu, Chengjun Feng, Linxiao Xing, Yazhe Ren, Bangshen Qi, Peng Zhang and Chengxuan Tan

Water 2022, 14(3), 410; https://doi.org/10.3390/w14030410 - 29 Jan 2022

Cited by 3 | Viewed by 2970

Abstract

The Xiong’an New Area is abundant in geothermal resources due to its unique geological structure. To address whether large-scale deep geothermal exploitation will induce a fault slip, we first determined the initial in situ stress field using shallow (~4000 m) in situ stress [...] Read more.

The Xiong’an New Area is abundant in geothermal resources due to its unique geological structure. To address whether large-scale deep geothermal exploitation will induce a fault slip, we first determined the initial in situ stress field using shallow (~4000 m) in situ stress measurements from the North China plain. After characterizing the in situ stress field, we analyzed the initial stability of the main active faults in the sedimentary strata of the Rongcheng deep geothermal reservoir based on the Mohr–Coulomb failure criteria. Assuming that this area will be subjected to forty years of continuous fluid injection, we calculated the excess pore pressure in the deep geothermal reservoir and, subsequently, estimated the fault slip potential of the main active faults in this region from 2021 to 2060. Our results indicated that both the in situ stress field in the shallow crust of the Xiong’an New Area and the Middle-Late Pleistocene active faults will initially maintain a stable state. With constant fluid injection for forty years at six geothermal wells in the Rongcheng deep geothermal reservoir, the maximum superposed excess pore pressure at a single well is 18 MPa; this excess pore pressure value impacts the stress state of faults within 8 km of the well location. These pore pressure perturbations heavily impact the F5-10, F5-11, and F9-2 segments of the Rongcheng uplift boundary fault, with FSP values of 92%, 23%, and 47% in 2060, respectively. Porosity exacts little impact on the fault slip potential on the boundary fault segments of F5-10 and F9-2 in the Rongcheng deep geothermal reservoir, while an enhanced permeability can weaken the FSP values for these faults. The predicted maximum moment magnitude of an induced earthquake due to continuous injection of forty years can be up to M_w 5.0 with a 5% fluid loss in the Rongcheng deep geothermal reservoir. Long-term water injection may increase the ambient thermoelastic stress to the point where faults in a critical (or subcritical) stress state become unstable. The results can provide a reference for geothermal development in terms of injection rate and locations of geothermal wells. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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21 pages, 43748 KiB

Open AccessArticle

Hydrochemical Characteristics of Earthquake-Related Thermal Springs along the Weixi–Qiaohou Fault, Southeast Tibet Plateau

by Huiling Zhou, Xiaocheng Zhou, Hejun Su, Ying Li, Fengli Liu, Shupei Ouyang, Yucong Yan and Ronglong Bai

Water 2022, 14(1), 132; https://doi.org/10.3390/w14010132 - 5 Jan 2022

Cited by 15 | Viewed by 4290

Abstract

The Weixi–Qiaohou Fault (WQF) is considered an important zone of the western boundary of the Sichuan–Yunnan block, and its seismicity has attracted much attention after a series of moderate–strong earthquakes, especially the Yangbi Ms6.4 earthquake that occurred on 21 May 2021. In [...] Read more.

The Weixi–Qiaohou Fault (WQF) is considered an important zone of the western boundary of the Sichuan–Yunnan block, and its seismicity has attracted much attention after a series of moderate–strong earthquakes, especially the Yangbi Ms6.4 earthquake that occurred on 21 May 2021. In the present research, we investigate major and trace elements, as well as hydrogen and oxygen isotopes, of 10 hot springs sites located along the WQF, which are recharged by infiltrated precipitation from 1.9 to 3.1 km. The hydrochemical types of most analyzed geothermal waters are HCO₃SO₄-Na, SO₄Cl-NaCa, and SO₄-Ca, proving that they are composed of immature water and thus are characterized by weak water–rock reactions. The heat storage temperature range was from 44.1 °C to 101.1 °C; the circulation depth was estimated to range between 1.4 and 4.3 km. The results of annual data analysis showed that Na⁺, Cl⁻, and SO₄²⁻ in hot springs decreased by 11.20% to 23.80% north of the Yangbi Ms5.1 earthquake, which occurred on 27 March 2017, but increased by 5.0% to 28.45% to the south; this might be correlated with the difference in seismicity within the fault zone. The results of continuous measurements of NJ (H1) and EYXX (H2) showed irregular variation anomalies 20 days before the Yangbi Ms6.4 earthquake. In addition, Cl⁻ concentration is more sensitive to near-field seismicity with respect to Na⁺ and SO₄²⁻. We finally obtained a conceptual model on the origin of groundwater and the hydrogeochemical cycling process in the WQF. The results suggest that anomalies in the water chemistry of hot spring water can be used as a valid indicator of earthquake precursors. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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14 pages, 3322 KiB

Open AccessFeature PaperArticle

Groundwater Radon Precursor Anomalies Identification by EMD-LSTM Model

by Xiaobo Feng, Jun Zhong, Rui Yan, Zhihua Zhou, Lei Tian, Jing Zhao and Zhengyi Yuan

Water 2022, 14(1), 69; https://doi.org/10.3390/w14010069 - 1 Jan 2022

Cited by 15 | Viewed by 3168

Abstract

Groundwater radon concentrations can reflect the changes of crustal stress and strain. Scholars and scientific institutions have also recorded groundwater radon precursor anomalies before earthquakes. Therefore, groundwater radon monitoring is an effective means of predicting seismic activities. However, the variation of radon concentrations [...] Read more.

Groundwater radon concentrations can reflect the changes of crustal stress and strain. Scholars and scientific institutions have also recorded groundwater radon precursor anomalies before earthquakes. Therefore, groundwater radon monitoring is an effective means of predicting seismic activities. However, the variation of radon concentrations within groundwater is not only affected by structural factors, but also by environmental factors, such as air pressure, temperature, and rainfall. This causes difficulty in identifying the possible precursor anomalies. Therefore, the EMD-LSTM model is proposed to identify the radon anomalies. This study investigated the time series data of groundwater radon from well #32 located in Sichuan province. Three models (including the LSTM (Long Short-Term Memory) model with auxiliary data, the EMD-LSTM (Empirical Mode Decomposition Long Short-Term Memory) model with auxiliary data, and the EMD-LSTM model without auxiliary data) were developed in order to predict groundwater radon variations. The results indicated that the prediction accuracy of the EMD-LSTM model was much higher than that of the LSTM model, and the EMD-LSTM model without auxiliary data also can obtain an ideal prediction result. Furthermore, the different durations of seismic activities T (T = ±10, ±30, ±50, and ±100) were also investigated by comparing the identification results. The identification rate of the precursor anomalies was the highest when T = ±30. The EMD-LSTM model identified five possible radon anomalies among the seven selected earthquakes. Taking well #32 as an example, we provided a promising method, that was the EMD-LSTM model, to detect the groundwater radon anomalies. It also suggested that the EMD-LSTM model can be used to identify the possible precursor anomalies within future studies. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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15 pages, 4914 KiB

Open AccessArticle

Remote Triggering of Damage Followed by Healing Recorded in Groundwater Pressure

by Eyal Shalev, Hallel Lutzky, Ittai Kurzon and Vladimir Lyakhovsky

Water 2021, 13(24), 3656; https://doi.org/10.3390/w13243656 - 20 Dec 2021

Cited by 2 | Viewed by 2823

Abstract

Water levels in three adjacent water wells in the Yarmouk Gorge area have all responded to the 2020 Elazığ Mw 6.8 teleseismic earthquake. Water levels in two aquifers exhibited reciprocal behavior: during the first eight days after the earthquake, water level decreased by [...] Read more.

Water levels in three adjacent water wells in the Yarmouk Gorge area have all responded to the 2020 Elazığ Mw 6.8 teleseismic earthquake. Water levels in two aquifers exhibited reciprocal behavior: during the first eight days after the earthquake, water level decreased by 40 cm in the deeper highly confined aquifer, and increased by 90 cm in the shallower less confined aquifer. The recovery of the water levels in both aquifers continued for at least three months. We interpret these observations as reflecting the increase in damage along the fault at the Yarmouk Gorge. Ground shaking increased the damage and permeability of this fault, temporarily connecting the two aquifers, allowing flow from the deep aquifer to the shallow one. Model results showing decreased permeability suggest that the fault healed by one order of magnitude within three days. This is the first documentation of decrease in permeability in a fault zone within such short time scales. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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16 pages, 3525 KiB

Open AccessFeature PaperArticle

Hydrogeochemistry and Precursory Anomalies in Thermal Springs of Fujian (Southeastern China) Associated with Earthquakes in the Taiwan Strait

by Bo Wang, Xiaocheng Zhou, Yongsheng Zhou, Yucong Yan, Ying Li, Shupei Ouyang, Fengli Liu and Jun Zhong

Water 2021, 13(24), 3523; https://doi.org/10.3390/w13243523 - 9 Dec 2021

Cited by 17 | Viewed by 3050

Abstract

Analyzing the hydrochemical composition in thermal springs is an advantageous method for studying the coupling mechanism of the deep and shallow fluids in active fault zones. Here we conducted sampling in 30 thermal springs near fault zones in Fujian Province, and the major [...] Read more.

Analyzing the hydrochemical composition in thermal springs is an advantageous method for studying the coupling mechanism of the deep and shallow fluids in active fault zones. Here we conducted sampling in 30 thermal springs near fault zones in Fujian Province, and the major elements, trace elements, silica, stable isotopes (δD and δ¹⁸O) and strontium isotopes were tested in the laboratory. The results show that (1) the thermal springs in the study area can be divided into six types according to the content of the major elements: HCO₃-Na, HCO₃·SO₄-Na, Cl·HCO₃-Na, Cl-Na, Cl-Na·Ca and HCO₃·SO₄-Ca; (2) hydrogen and oxygen isotopes indicate that precipitation is the main source of recharge for thermal springs in the study area, and the recharge height is between 258 m and 1859 m; (3) the content of SiO₂ in the thermal spring varies from 18.1 mg/L to 59.3 mg/L. The geothermal reservoir temperature calculated is 90~226 °C, and the circulation depth is 2.9~5.4 km, except for the W10 thermal spring, whose circulation depth is 8.4 km; and (4) the ⁸⁷Sr/⁸⁶Sr of the thermal springs in southwestern Fujian and eastern Fujian has obviously different characteristics, indicating the influence of different rock formations on the groundwater cycle process. Additionally, a continuous measurement of the main anions and cations was performed in five thermal springs every three days since January 2020. There were obvious abnormal changes in the hydrochemical compositions, chlorine in four of the five springs, sodium at three springs, and four ions at one spring, which all showed abnormal high-value changes by 15% to 80%, and which occurred 85~168 days prior to the M6.1 earthquake in Hualien, Taiwan. An inspiration could be provided for obtaining effective earthquake precursor anomalies by monitoring the change in ion concentration in thermal springs. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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15 pages, 4686 KiB

Open AccessArticle

Hydrochemical Characteristics of Groundwater at the Epicenter of the 2021 Biru M6.1 Earthquake in Central Tibet

by Pengtao Yang, Xiaolong Sun, Dongying Liu, Zhongtai He and Yongsheng Li

Water 2021, 13(21), 3111; https://doi.org/10.3390/w13213111 - 4 Nov 2021

Cited by 2 | Viewed by 3087

Abstract

Groundwater is undoubtedly important for water security and eco-environmental protection, especially in areas that experience earthquakes. Analyzing the characteristics and variation of groundwater after an earthquake is significant to obtain a better understanding of the seismic risk and rational management of groundwater resources. [...] Read more.

Groundwater is undoubtedly important for water security and eco-environmental protection, especially in areas that experience earthquakes. Analyzing the characteristics and variation of groundwater after an earthquake is significant to obtain a better understanding of the seismic risk and rational management of groundwater resources. This study investigated the hydrogeochemical characteristics of groundwater at the epicenter of the 2021 Biru M6.1 earthquake in central Tibet, southwest China, using 23 water samples. The results showed that: (1) the hydrochemical type, hydrogen and oxygen isotope ratios, and SiO₂ concentrations of three hot spring water samples in the study area were significantly different from those of samples taken elsewhere, indicating that the hot spring water originates from deeper geothermal reservoirs and has undergone more distant migration and longer fractionation processes; (2) the geochemical characteristics of groundwater from some sampling sites in the epicentral area were apparently distinct from those of other shallow groundwater or surface water samples, suggesting that the groundwater environment in the epicentral area has been affected by the earthquake. Along with the macroscopic groundwater responses in the epicentral area after the earthquake, we investigated the influencing mechanisms of the earthquake on the regional groundwater environment. We conclude that a shorter distance from the epicenter to the seismogenic fault leads to a greater possibility of the generation of new fractures, which then induce macroscopic responses and chemical characteristic variations for groundwater. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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14 pages, 37498 KiB

Open AccessArticle

Determining Stress State of Source Media with Identified Difference between Groundwater Level during Loading and Unloading Induced by Earth Tides

by Huaizhong Yu, Chen Yu, Yuchuan Ma, Binbin Zhao, Chong Yue, Rong Gao and Yulong Chang

Water 2021, 13(20), 2843; https://doi.org/10.3390/w13202843 - 12 Oct 2021

Cited by 8 | Viewed by 2233

Abstract

The groundwater level might be adopted as a useful tool to explore pre-seismic stress change in the earth crust, because it circulates in the deep crust and should be altered by the processes associated with the preparation of earthquakes. This work makes a [...] Read more.

The groundwater level might be adopted as a useful tool to explore pre-seismic stress change in the earth crust, because it circulates in the deep crust and should be altered by the processes associated with the preparation of earthquakes. This work makes a new attempt that applies the load/unload response ratio (LURR) technique to study the stress state of the source media before the large earthquakes by calculating the ratio between the water levels during the loading and unloading phases. The change of Coulomb failure stress induced by earth tides in the tectonically preferred slip direction on the fault surface of the mainshock is adopted for differentiating the loading and unloading periods. Using this approach, we tested the groundwater level in the wells near the epicenters of some large earthquakes that occurred in the Sichuan-Yunnan region of southwest China. Results show that the LURR time series fluctuated narrowly around 1.0 for many years and reached anomalously high peaks 2~8 months prior to the mainshocks. For the earthquakes with multiple observation wells, the magnitude of the maximum values decreases with the distance from the epicenter. The underlying physics of these changes should be caused by the pre-seismic dilatancy. The corresponding volume variations in the crust could be observed in the geodetic time series in the same neighborhoods and during the same period. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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11 pages, 1649 KiB

Open AccessArticle

Relationship between Earthquake-Induced Hydrologic Changes and Faults

by Yuchuan Ma, Guangcai Wang, Rui Yan, Bo Wang, Huaizhong Yu, Chen Yu, Chong Yue and Yali Wang

Water 2021, 13(19), 2795; https://doi.org/10.3390/w13192795 - 8 Oct 2021

Cited by 2 | Viewed by 2678

Abstract

Hydraulic properties of fault zones are important to understanding the pore pressure development and fault stability. In this work, we examined the relationship between water level changes caused by the 2008 Wenchuan M_w 7.9 earthquake and faults using four wells with the [...] Read more.

Hydraulic properties of fault zones are important to understanding the pore pressure development and fault stability. In this work, we examined the relationship between water level changes caused by the 2008 Wenchuan M_w 7.9 earthquake and faults using four wells with the same lithology around the Three Gorges Dam, China. Two of the wells penetrating the fault damage zones recorded sustained water level changes, while the other two wells that are not penetrating any fault damage zones recorded transient water level changes. The phase shift and tidal factor calculated from water level, a proxy of permeability and storage coefficient, revealed that both the permeability and storage coefficient changed in the two wells penetrating the fault damage zones, while the other two wells not penetrating the fault damage zone did not show any change in permeability and storage coefficient. Thus, we tentatively suggest that faults may play an important controlling role on earthquake-induced hydrologic changes because the detrital or clogging components in the fractures may be more easily removed by seismic waves. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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19 pages, 5635 KiB

Open AccessFeature PaperArticle

Hydrogeochemical Characteristics of Hot Springs and Their Short-Term Seismic Precursor Anomalies along the Xiaojiang Fault Zone, Southeast Tibet Plateau

by Chenhua Li, Xiaocheng Zhou, Yucong Yan, Shupei Ouyang and Fengli Liu

Water 2021, 13(19), 2638; https://doi.org/10.3390/w13192638 - 25 Sep 2021

Cited by 27 | Viewed by 4075

Abstract

Significant hydrogeochemical changes may occur prior- and post-earthquakes. The Xiaojiang fault zone (XJF), situated in a highly deformed area of the southeastern margin of the Tibetan Plateau, is one of the active seismic areas. In this study, major and trace elements, and hydrogen [...] Read more.

Significant hydrogeochemical changes may occur prior- and post-earthquakes. The Xiaojiang fault zone (XJF), situated in a highly deformed area of the southeastern margin of the Tibetan Plateau, is one of the active seismic areas. In this study, major and trace elements, and hydrogen and oxygen isotopes of 28 sites in hot springs along the XJF were investigated from June 2015 to April 2019. The meteoric water acts as the primary water source of the hot spring in the XJF and recharged elevations ranged from 1.8 to 4.5 km. Most of the hot spring water in the study area was immature water and the water–rock reaction degree was weak. The temperature range was inferred from an equation based on the SiO₂ concentration and chemical geothermal modeling: 24.3~96.0 °C. The circulation depth for the springs was estimated from 0.45 to 4.04 km. We speculated the meteoric water firstly infiltrated underground and became heated by heat sources, and later circulated to the earth’s surface along the fault and fracture and finally constituted hot spring recharge. Additionally, a continuous monitoring was conducted every three days in the Xundian hot spring since April 2019, and in Panxi and Qujiang hot springs since June 2019. There were short-term (4–35 d) seismic precursor anomalies of the hydrochemical compositions prior to the Xundian M_L4.2, Dongchuan M_L4.2, and Shuangbai M_L5.1 earthquakes. The epicentral distance of anomalous sites ranged from 19.1 to 192.8 km. The anomalous amplitudes were all over 2 times the anomaly threshold. The concentrations of Na⁺, Cl^?, and SO₄^2? are sensitive to the increase of stress in the XJF. Modeling on hydrology cycles of hot springs can provide a plausible physicochemical basis to explain geochemical anomalies in water and the hydrogeochemical anomaly may be useful in future earthquake prediction research of the study area. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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18 pages, 2795 KiB

Open AccessArticle

Pilot-Scale Groundwater Monitoring Network for Earthquake Surveillance and Forecasting Research in Korea

by Hyun A Lee, Se-Yeong Hamm and Nam C. Woo

Water 2021, 13(17), 2448; https://doi.org/10.3390/w13172448 - 6 Sep 2021

Cited by 14 | Viewed by 3272

Abstract

Although there is skepticism about the likelihood of predictive success, research on the prediction of an earthquake through precursory changes in natural parameters, including groundwater, has continued for decades. One of the promising precursors is the changes in groundwater, i.e., the level and [...] Read more.

Although there is skepticism about the likelihood of predictive success, research on the prediction of an earthquake through precursory changes in natural parameters, including groundwater, has continued for decades. One of the promising precursors is the changes in groundwater, i.e., the level and composition of groundwater, and the monitoring networks are currently operated to observe earthquake-related changes in several countries situated at the seismically active zone. In Korea, the seismic hazards had not been significantly considered for decades since the seismic activity was relatively low; however, the public demands on the management and prediction of earthquakes were raised by two moderate-size earthquakes which occurred in 2016 and 2017. Since then, a number of studies that were initiated in Korea, including this study to establish a pilot-scale groundwater-monitoring network, consisted of seven stations. The network is aimed at studying earthquake-related groundwater changes in the areas with relatively high potentials for earthquakes. Our study identified a potential precursory change in water levels at one particular station between 2018 and 2019. The observed data showed that most monitoring stations are sufficiently isolated from the diurnal natural/artificial activities and a potential precursory change of water level was observed at one station in 2018. However, to relate these abnormal changes to the earthquake, continuous monitoring and analysis are required as well as the aid of other precursors including seismicity and geodetic data. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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15 pages, 5623 KiB

Open AccessFeature PaperArticle

Two Mechanisms of Earthquake-Induced Hydrochemical Variations in an Observation Well

by Zhihua Zhou, Jun Zhong, Jing Zhao, Rui Yan, Lei Tian and Hong Fu

Water 2021, 13(17), 2385; https://doi.org/10.3390/w13172385 - 30 Aug 2021

Cited by 10 | Viewed by 3204

Abstract

Due to frequent large earthquakes in the Lanping-Simao fault basin—located in China’s Yunnan Province—the Simao observation well has observed groundwater discharge, as well as Ca²⁺, Mg²⁺, and HCO₃^? concentrations every day between 2001–2018. Over 18 years of [...] Read more.

Due to frequent large earthquakes in the Lanping-Simao fault basin—located in China’s Yunnan Province—the Simao observation well has observed groundwater discharge, as well as Ca²⁺, Mg²⁺, and HCO₃^? concentrations every day between 2001–2018. Over 18 years of observations, M ? 5.6 earthquakes within a radius of 380 km from the well were seen to cause hydrochemical variations. In this study, we investigated CO₂ release and groundwater mixing as possible causes of regional earthquake precursors, which were caused by the characteristics of the regional structure, lithology, water-rock reactions, and a GPS velocity field. Precursory signals due to CO₂ injection are normally short-term changes that take two months. However, groundwater mixing linked to earthquakes was found to take, at the earliest, 15 months. The proportion of shallow water that contributes to mixing was found to significantly increase gradually with the stronger regional strain. These finding delineate the two mechanisms of earthquake-induced hydrochemical variations in an observation well, and would contribute to a better understanding of chemical changes before events in the Simao basin. Full article

(This article belongs to the Special Issue Earthquakes and Groundwater)

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