Evaluation of groundwater hydrochemical characteristics and mixing behavior in the Daying and Qicun geothermal systems,Xinzhou Basin

This paper examines groundwater hydrochemical characteristics during mixing between thermal and non-thermal groundwater in low-to-medium temperature geothermal fields. A case study is made of Daying and Qicun geothermal fields in the Xinzhou basin of Shanxi province, China. The two geothermal fields have similar flow patterns, with recharge sourced from precipitation in mountain areas heated through a deep cycle, before flowing into overlying Quaternary porous aquifers via fractures. Hydrochemical features of 60 ground- and surface water samples were examined in the context of hydrogeologic information. The average temperatures of the deep geothermal reservoirs are estimated to be 125 °C in Daying field, and 159 °C in Qicun field, based on Na–K–Mg geothermometry, while slightly lower estimates are obtained using silica geothermometers. Hydrochemical features of thermal water are distinct from cold water. Thermal groundwater is mainly Cl·SO₄–Na type, with high TDS, while non-thermal groundwater is mostly HCO₃–Ca·Mg and HCO₃–Ca type in the Daying and Qicun regions, respectively. Hydrogeochemical processes are characterized by analyzing ion ratios in various waters. Higher contents of some minor elements in thermal waters, such as F, Si, B and Sr, are probably derived from extended water–rock interaction, and these elements can be regarded as indicators of flow paths and residence times. Mixing ratios between cold and thermal waters were estimated with Cl, Na, and B concentrations, using a mass balance approach. Mixing between ascending thermal waters and overlying cold waters is extensive. The proportion of water in the Quaternary aquifer derived from a deep thermal source is lower in Daying geothermal field than in Qicun field (5.3–7.3% vs. 6.3–49.3%). Mixing between thermal and non-thermal groundwater has been accelerated by groundwater exploitation practices and is enhanced near faults. Shallow groundwater composition has also been affected by irrigation with low-temperature thermal water.     

Estimation of reservoir temperature using silica and cationic solutes geothermometers:a case study in the Tengchong geothermal area

Reservoir temperature estimation is vitally important for assessing the exploitation potential of a geothermal field.In this study,the concentrations of major chemical constituents in geothermal water sampled from boiling and hot springs in the Tengchong hydrothermal area were measured,and quartz and cationic solutes geothermometers were used to calculate subsurface temperatures.Log(Q/K) diagrams and Na-K-Mg triangular diagrams were applied to evaluating the equilibrium status of geothermal water samples with regard to reservoir minerals,and results were used to select suitable geothermometers.The results show that samples RH01,RH03,RH04,RH05,and LL16 were in or very close to full equilibrium with the selected minerals,and therefore a NaK geothermometer is appropriate.A K/Mg geothermometer,however,is applicable to LP08 and PZH18 whose chemical compositions adjusted to the shallow reservoir temperatures during their re-equilibrium processes.In contrast,cationic solute geothermometers are unsuitable for SQ20 and RH07,which are categorized as immature water in the Na-K-Mg diagram;a quartz geothermometer was adopted to evaluate the corresponding subsurface temperatures of these samples.According to the reservoir temperature estimation made in this study,there is at least one high-temperature reservoir below Rehai with a possible temperature range of 210-270 ℃.     

The use of GPR for characterizing underground weathered profiles in the sub-humid tropics

Ground penetrating radar (GPR) has been used as a tool to access information about ground subsurface features. Such information is very important for different types of studies, varying from those related to archeological research to those studying geological elements of bedrock. More recently, however, GPR has been increasingly applied to environmental studies, especially for soil research. This paper presents the results of an application of GPR for the study of weathered profiles. GPR was used to discover the degree of trustworthiness of the information on the ground subsurface through the interpretation of the results of the radar sections as well as the data collected from boreholes, which reached until 21 m. The results show a relatively high degree of details obtained by GPR, indicating the possibility of speeding up ground subsurface surveys related to geomorphological, geological, and pedological studies.     

Simple models for estimating period‐shift and damping in soil

This study describes the development of a simple, heuristic manual calculation procedure for estimating the site period‐shift factor and soil damping ratio, with appropriate considerations for the level of shaking, impedance contrast between soil and bedrock interface and the plasticity of the soil layers. Essentially, the analogy of a building shear‐frame has been used to represent the seismic response behaviour of a soil column. The proposed procedure has been verified by comparing the predictions with results obtained directly from non‐linear shear wave analyses of soil column models. Copyright © 2006 John Wiley & Sons, Ltd.     

华北北部地热田区地下流体观测中出现的问题及应对方法

在对华北北部地热田区自流热水井地下流体前兆观测及现状进行广泛调查的基础上,分析地震地下流体观测井因过度开采热水而引起观测井断流,并由此引发的一系列严重问题。介绍为此采取的测项调整、观测装置改造、观测条件改变、观测环境保护区的划定等各种措施。指出测项调整、观测装置与观测条件改变的有效性与局限性,强调解决问题的根本出路在于观测环境的保护,同时说明当前落实观测环境保护遇到的困难。     

太湖水体叶绿素浓度反演模型适宜性分析

为确定适合太湖水体叶绿素的反演算法,为同类卫星数据的建模和应用提供参考,本文根据太湖2007年11月、2009年4月和2011年8月实测水质参数以及同步光谱数据,结合水色遥感传感器MODIS、MERIS、GOCI及我国自主发射的HJ-1号卫星CCD传感器波段参数,基于差值模型、比值模型、三波段模型及APPEL模型,分别建立太湖水体叶绿素浓度反演模型,并分析模型的适宜性.结果显示,基于不同传感器数据APPEL模型的决定系数为0.7308~0.8107,模型相对误差为15%~24%,均方根误差为21%~32%;三波段模型基于不同传感器数据拟合的决定系数为0.6014~0.7610,相对误差为28%~36%,相对均方根误差为39%~46%;差值模型决定系数为0.4954~0.7244,相对误差为39%~53%,相对均方根误差为51%~72%;比值模型决定系数为0.4918~0.7098,相对误差为41%~55%,相对均方根误差为56%~75%.相比较而言,APPEL模型的稳定性较强,适合于不同传感器数据的太湖水体叶绿素浓度的反演.此外,相应不同传感器波段位置、波段宽度对模型反演的精度和稳定性的影响也不同,当波段位置接近叶绿素特征波长时,较窄的波宽有利于模型精度的提高,波段位置和叶绿素浓度特征波长相差较大时,合理增加波谱范围有利于叶绿素特征信息的获取.     

Methods for estimating Curie temperatures of titanomaghemites from experimentalJs-T data

Methods for determining the Curie temperature (T_c) of titanomaghemites from experimental saturation magnetization-temperature (J_s-T) data are reviewed.J_s-T curves for many submarine basalts and synthetic titanomaghemites are irreversible and determining Curie temperatures from these curves is not a straightforward procedure. Subsequently, differences of sometimes over 100°C in the values ofT_c may result just from the method of calculation. Two methods for determiningT_c will be discussed: (1) the graphical method, and (2) the extrapolation method. The graphical method is the most common method employed for determining Curie temperatures of submarine basalts and synthetic titanomaghemites. The extrapolation method based on the quantum mechanical and thermodynamic aspects of the temperature variation of saturation magnetization nearT_c, although not new to solid state physics, has not been used for estimating Curie temperatures of submarine basalts. The extrapolation method is more objective than the graphical method and uses the actual magnetization data in estimatingT_c.     

Temperature/flow statistics and thermomechanics of low-temperature geothermal systems in Iceland

A survey of low-temperature geothermal activity in Iceland shows that there is a strong positive correlation between the temperature and the mass flow of the systems. The relation is very clearly displayed by the thermal systems in Central Northern Iceland. Subdividing the temperature interval from 20/dgC to 100°C into 8 intervals of equal length and plotting the average system flow in each interval against the average temperature of the interval we find that the mass flow increases with the temperature. At the lower end this relation is the result of a conductive cooling of the thermal water as it ascends to the surface. At temperatures above 50°C convective effects appear to be the dominant cause. A very simple lumped element analysis of the low-temperature systems results in reasonable estimates of important flow parameters. The convective downward migration of fracture spaces along the walls of mafic dikes appears to be a dominant thermomechanical process in the development of the low-temperature systems in Northern Iceland.     

Direct use of PGV for estimating peak nonlinear oscillator displacements

A predictive model is presented for estimating the peak inelastic oscillator displacements (S_d,ie) from peak ground velocity (PGV). The proposed model accounts for the variation of S_d,ie for bilinear hysteretic behavior under constant ductility (µ) and normalized lateral strength ratio (R) associated with postyield stiffness ratios of α=0 and 5%. The regression coefficients are based on a ground‐motion database that contains dense‐to‐stiff soil site recordings at distances of up to 30 km from the causative fault. The moment magnitude ( M ) range of the database is 5.2? M ?7.6 and the ground motions do not exhibit pulse‐dominant signals. Confined to the limitations imposed by the ground‐motion database, the model can estimate S_d,ie by employing the PGV predictions obtained from the attenuation relationships (ground‐motion prediction equations). In this way, the influence of important seismological parameters can be incorporated to the variation of S_d,ie in a fairly rationale manner. This feature of the predictive model advocates its implementation in the probabilistic seismic hazard analysis that employs scalar ground‐motion intensity indices. Various case studies are presented to show the consistent estimations of S_d,ie by the proposed model. The error propagation in the S_d,ie estimations is also discussed when the proposed model is associated with attenuation relationships. Copyright © 2008 John Wiley & Sons, Ltd.     

Magma mixing and magma plumbing systems in island arcs

Petrographic features of mixed rocks in island arcs, especially those originating by the mixing of magmas with a large compositional and temperature difference, such as basalt and dacite, suggest that the whole mixing process from their first contact to the final cooling (= eruption) has occurred continuously and in a relatively short time period. This period is probably less than several months, considerably shorter than the whole volcanic history. There may also be a prolonged quiescent interval, lasting longer than several days, between the magmas' contact and the mechanical mixing. This interval will allow the basic magma to cool and produce a semi-solidified boundary which is later disrupted by flow movements to produce basic inclusions.Mixing of magmas of contrasting chemical composition need not be the inevitable consequence of the contact of the magmas. It is, however, made more probable by forced convection caused by motive force such as the injection of a basic magma into an acidic magma chamber. A short interval between their initial contact and the final eruption requires that the acid magma chamber has a small volume, of the same order or less than that the introduced basic magma.The volcanic activity of Myoko volcano, central Japan, of the last 100,000 years shows alternate eruptions of hybrid andesite by mixing of basaltic and dacitic magmas, and non-mixed basalt to basaltic andesite. There was a repose period of 20,000 to 30,000 years between eruptions. The acidic chamber, eventually producing the mixed andesite activity, is formed during the repose period by the « in situ » solidification of the original basic magma against its wall. The volume of the chamber is very small, probably about 10^–2 km³. Basaltic magma with constant chemical composition is supplied to the shallow chamber from another deep seated basaltic chamber. The volume of the shallow magma chamber may be critical to the characteristics of volcanic activity and its products.     

Chemical and isotopic prediction of aquifer temperatures in the geothermal system at Long Valley, California

Temperatures of aquifers feeding thermal springs and wells in Long Valley, California, estimated using silica and Na-K-Ca geothermometers and warm spring mixing models, range from 160/dg to about 220°C. This information was used to construct a diagram showing enthalpy-chloride relations for the various thermal waters in the Long Valley region. The enthalpy-chloride information suggests that a 282 ± 10°C aquifer with water containing about 375 mg chloride per kilogram of water is present somewhere deep in the system. That deep water would be related to 220°C Casa Diablo water by mixing with cold water, and to Hot Creek water by first boiling with steam loss and then mixing with cold water. Oxygen and deuterium isotopic data are consistent with that interpretation. An aquifer at 282°C with 375 mg/kg chloride implies a convective heat flow in Long Valley of 6.6 × 10⁷ cal/s.     

The calibration and use of pressure transducers in tensiometer systems

The uncertainty in a transducer/tensiometer system was assessed with temperature and pressure calibrations. A reference transducer/tensiometer pair was used to factor out temperature related deviations from two monitoring pairs. The reference pair removed most of the deviations, resulting in a high estimate of precision. In contrast to earlier reports of high accuracy, these estimates of accuracy were considerably reduced by a time correlated residual pattern. The calibrations suggested that the electronic components may be responsible for these residual errors and illustrated the need for experimentation which isolates the error among groups of components. The complexity of transducer/tensiometer networks, and the differing response of each component to thermal loading, demonstrated the necessity of using a reference system, which when properly designed can yield reliable pressure readings for soil water.     

Aquifer chemistry of the Puga and Chumatang high temperature geothermal systems in India

Results of a chemical study of the fluids from drill holes and hot springs of Puga and Chumatang areas in the northwestern part of the Himalaya are presented and discussed in this paper. The thermal waters of Puga and Chumatang are of Na-HCO₃-Cl and Na-HCO₃ types, respectively. A comparison between these waters, their chemical classification and activity studies suggest a flow path within a quartzitic-schistose basement, containing quartz, K-feldspar and illite, and in clayey terrains containing montmorillonite and illite.The chemistry of thermal waters also indicate their association with magmatic activity. The chemical geothermometers indicate the possible existence of a geothermal reservoir at Puga with temperature ≈250°C. The Chumatang area has a comparatively cooler reservoir with a temperature of 150–180°C.     

Seismicity in the Rotorua and Kawerau geothermal systems,Taupo Volcanic Zone,New Zealand,based on improved velocity models and cross-correlation measurements

We analyze earthquakes occurring in and around the Rotorua and Kawerau geothermal systems, Taupo Volcanic Zone, New Zealand. The two data sets contain 504 and 1875 shallow (≤ 20 km deep) earthquakes, respectively, and span the 21 year period between 1984 and 2004. The arrival time data for these earthquakes are first used to calculate 1-D P- and S-wave seismic velocity models and accompanying station correction terms for both areas. In order to address the non-uniqueness of the joint hypocenter-velocity model estimation problem, we analyze suites of 1000 velocity models computed from random initial models. The final velocity models are well constrained, particularly at depths between 4 and 15 km, and consistent with the results obtained in previous seismic refraction studies of the central Taupo Volcanic Zone. Using a combination of cross-correlation-derived and catalog-based arrival times, we relocate subsets of the Rotorua and Kawerau data sets. In Rotorua, the relocated earthquakes cluster near the geothermally active parts of Rotorua City and beneath the Mount Ngongotaha rhyolite dome. Earthquake clusters and alignments reveal seismogenic structures in the mid-crust whose positions and geometries are consistent with previously published fault mechanisms and known near-surface faults. In Kawerau, the earthquakes within the geothermal field align along northeast-trending lineations, consistent with the predominant alignment of surface-mapped faults in the area.     

Evaluation of reservoir temperatures and local utilization of geothermal waters of the Konkan Coast, India

Geochemical studies on fifteen geothermal manifestations (38–70°C) from the Konkan coast geothermal province of India have been used to evaluate the reservoir temperatures. Activity studies of the minerals and the waters present in the reservoirs suggest that the thermal waters are in equilibrium with montmorillonite, kaolinite and quartz at about 100°C. Reservoir temperatures of these geothermal systems as estimated by geochemical thermometers, are 88 to 128°C, and thus too low for economic electricity production.     

A method for estimating sediment budgets of washover deposits using digital terrain models

Washover fans are located on small barriers in fetch-limited micro-tidal coastal environments in Denmark. These washover fans are formed during high-energy storm events and we present a method to quantify their volumes and to estimate sediment exchanges between washover fans and their adjacent morphologies. We use high resolution digital terrain models (DTMs) based on light detection and ranging (LiDAR) data. We have delineated landforms using known methods of scale analysis and geomorphometric classification. We quantified volumes of the delineated landforms and estimated the related sediment budgets. These computed volumes were compared using different pre-depositional surfaces. Finally, we assessed the sediment exchange and associated sources of sediments of the washover fans. We applied a scale analysis to determine suitable DTM resolution and focal statistics window size as input to a geomorphometric classification analysis. Landform areas and landforms were delineated using morphometric threshold values, and volumes and sediment budgets of the delineated landforms were computed using different assumptions to define the pre-depositional surface. Resulting washover fan volumes were validated against digital elevation model (DEM) of difference (DoD) derived volumes. Sediment budgets were derived from representative volumes of the washover fans and adjacent berms. We show that quantification of washover features derived from DTMs, using geomorphometric analysis is feasible and that the presented approach provides estimates of washover deposit volumes with an accuracy between 1% and 28% compared to control volumes. © 2021 John Wiley & Sons, Ltd.     

The use of reduced finite element models in system identification

An a priori, analytical model in system identification of vibrating structures is improved by input and output measurements with least square fitting. The structure is modelled by the finite element method. Finite element models usually need a large number of degrees of freedom to simulate a small number of lower spectrum eigenfrequencies with accuracy. The large finite element model is reduced to a subspace of significant eigenfrequencies. The size of the subspace is chosen with regard to the frequency content of the measured data and the accuracy of the large analytical model. An identification method is formulated for the large analytical model. This procedure improves system parameters in the matrices of the large model by measured input and output data with a least square functional. The objective function is consistently reduced, so that the whole identification procedure can be performed in the small subspace. The proposed reduction method permits very large and accurate analytical models to be used, and it decreases the computational cost of the identification procedure significantly. The computational efficiency is demonstrated on an in situ experiment of a radar tower.     

The practical use of simplicity in developing ground water models

The advantages of starting with simple models and building complexity slowly can be significant in the development of ground water models. In many circumstances, simpler models are characterized by fewer defined parameters and shorter execution times. In this work, the number of parameters is used as the primary measure of simplicity and complexity; the advantages of shorter execution times also are considered. The ideas are presented in the context of constructing ground water models but are applicable to many fields. Simplicity first is put in perspective as part of the entire modeling process using 14 guidelines for effective model calibration. It is noted that neither very simple nor very complex models generally produce the most accurate predictions and that determining the appropriate level of complexity is an ill-defined process. It is suggested that a thorough evaluation of observation errors is essential to model development. Finally, specific ways are discussed to design useful ground water models that have fewer parameters and shorter execution times.     

The use of simple process-based models in the estimate of water balances for mixed land use catchments in East Africa

Soil moisture measurements by the neutron probe method were analysed to provide the parameters required for a daily model of actual evaporation from three land uses—grassland, indigenous bamboo and plantation softwood—in the Aberdare range of hills, Kenya. These daily estimates of evaporation were summed to provide annual totals and used, on a percentage land cover basis, in water balance calculations for three experimental mixed land use catchments, two of which were undergoing land use change. The annual water use, given by the difference between rainfall inputs and streamflow outputs, of the undisturbed catchment could normally be predicted to within 10%, whereas differences in the predicted and measured water use of the other two catchments were related to the changes in vegetation.     

地热异常区不同含水层水化学组分差异

对天津周良庄地热区不同含水层水化学背景开展实验研究,结果发现：随含水层埋藏深度加大,气体组分变化较大,水氡、水汞、离子组分变化较平稳,水氡背景值偏低.在此基础上,从含水层岩性、取样条件、水化学组分特性、地质构造等方面,对不同含水层之间水化学组分的差异性进行分析,认为区域内特殊地质构造是影响差异性的重要因素.