High Conductivity Zone Research Articles

Electrical Conductivity of Eclogite, Amphibolite and Garnet-Quartz-Mica Schist with Implications for the Conductivity in the Qiangtang Terrane of Northern Tibetan Plateau

Understanding the electrical conductivity of high pressure metamorphic rocks is essential to constrain the compositions in the subduction zone and continental crust. In this study, we calculated the electrical conductivity for such rocks sampled from the central Qiangtang metamorphic belt in the northern Tibetan Plateau. The results reveal that, when aqueous fluids are absent, the conductivity of meta-mafic rocks (e.g., eclogite and amphibolite) is strikingly higher than that of meta-felsic rocks (e.g., garnet-quartz-mica schist). The conductivity of eclogite decreases due to the enrichment of amphibole, but this effect is diminished when a critical degree of amphibolization is reached. Our calculated conductivity of eclogite and amphibolite differs greatly from the experimentally derived results for the eclogites from other localities, partly owing to the strong effects of different mineral assemblages and chemical compositions on the conduction mechanisms and efficiencies. However, the disparity of conductivity between our calculated and the previously measured results for a similar amphibole-rich eclogite sampled from the same locality suggests that trails of highly conductive rutile-ilmenite aggregates may contribute to the higher bulk-rock conductivity in the laboratory measurements. Moreover, since the calculated conductivity of eclogite and amphibolite is not high enough at the temperatures relevant to their metamorphic thermal condition, partial melts or aqueous fluids originated from the upwelling asthenosphere are more likely to explain the anomalously high electrical conductivity zones in magnetotelluric images in the Qiangtang terrane in the northern Tibetan Plateau.

An Integrated Geophysical and Geochemical Investigation of an Open Dumpsite in a Sedimentary Formation

The extents of migration of leachate plumes and the probabilistic assessment of human health risks were carried out on Oke-Diya dumpsite, Sagamu, Southwestern Nigeria. Geophysical methods involving Very Low Frequency-Electromagnetic (VLF-EM) and Electrical Resistivity Topography (ERT) techniques, and Atomic Absorption Spectrometric (AAS) geochemical method were used to map and detect the presence and extent of leachate migration. The VLFEM pseudo-sections revealed conductive zones of responses 25 - 50 to a depth of about 15 m and approximated distance 50 m from the study area. The 2D and 3D ERT models delineated high conductive zones with very low resistivity values ranging from 0.551-6.54 and 2.4respectively. These conductive regions were observed to depths above 13.4 m and approximated distance 60 m from the study area in the 2D models. The 3D sections comprising of the horizontal depth slices, vertical planes and volumetric displays revealed regions with higher conductivity to a depth of about 21.9 m and approximated distance 50 m from the dumpsite. The mean concentrations of heavy metals Pb, Ni, Cd, Zn, Fe and Cu in the soil samples were higher than the concentrations in the control samples. The human health risk assessment indicated unacceptable values for non-carcinogenic adverse effects for both children and adults. The probabilistic cancer risks were within the acceptable range for Pb and unacceptable for Cd for both the children and adults. Generally, this study had identified areas of concentrated plumes accumulation and migration pathways, which were in agreement with earlier studies in sedimentary terrain.

Tibetan dichotomy exposed in the Canadian Shield: A lower crustal perspective

It has been hypothesized that much of central and eastern Tibet coincides with gravitationally driven flow of weak lower continental crust. Magnetotelluric profiles throughout Tibet reveal several deep crustal zones of high conductivity inferred to represent either melt-weakened channelized flow of deep crust or alternatively, migration of fluids or melts along shear zone-fault systems. In eastern Tibet, some workers suggest that deep crustal flow is diverted around cratonic lithosphere beneath the Sichuan basin. This behavior requires a weak versus strong rheological dichotomy in the lower crust. Evidence for this behavior is presented from a deeply exhumed granulite terrane (>0.6–1.6 GPa) in the western Canadian Shield. Data support the hypothesis that at 1.95–1.90 Ga, lower crust northwest of the >400 km-long Grease River shear zone was melt-weakened while lower crust southeast of the Grease River shear zone was dehydrated and strong. Strain localization and dextral transpressive shearing occurred at 1.91–1.90 Ga along the Grease River shear zone – the locus of a rheological dichotomy that represents a field-based analog for lower crust beneath the eastern Tibetan plateau. This work demonstrates that rheology of the lower continental crust can be spatially heterogeneous at <1 m2 to 100s of km2 scales. Deep crustal rheology also depends on fertility: melt weakening and flow during fluid-absent melting (>750°C) and granulite-grade metamorphism is favored in “first-cycle” metasedimentary biotite-rich protoliths, though melt extraction can decrease this fertility. Older and previously dehydrated poly-metamorphic granulites tend to be stronger and less prone to pervasive lower crustal flow.

Magnetotelluric imaging of the Mérida Andes and surrounding areas in Venezuela

SUMMARYThe Caribbean and South American tectonic plates bound the north-eastwards expulsion of the North Andean Block in western Venezuela. This complex geodynamic setting resulted in the formation of major strike-slip fault systems and sizeable mountain chains. The 100-km-wide Mérida Andes extend from the Colombian/Venezuelan border to the Caribbean coast. To the north and south, the Mérida Andes are bound by hydrocarbon-rich sedimentary basins. Knowledge of lithospheric structures, related to the formation of the Mérida Andes, is limited though, due to a lack of deep geophysical data. In this study, we present results of the first broad-band magnetotelluric profile crossing the Mérida Andes and the Maracaibo and Barinas–Apure foreland basins on a length of 240 km. Geoelectrical strike and dimensionality analysis are consistent with 1-D or 2-D subsurface structures for the sedimentary basins but also indicate a strong 3-D setting for the Mérida Andes. Using a combination of 2-D and 3-D modelling we systematically examined the influence of 3-D structures on 2-D inversions. Synthetic data sets derived from 3-D modelling allow identification and quantification of spurious off-profile features as well as smoothing artefact due to limited areal station coverage of data collected along a profile. The 2-D inversion models show electrically conductive basins with depths of 2–5 km for the Barinas-Apure and 2–7 km for the Maracaibo basins. A number of resistive bodies within the Maracaibo basin could be related to active deformation causing juxtaposition of older geological formations and younger basin sediments. The most important fault systems of the area, the Boconó and Valera Faults, cross-cut the Mérida Andes in NE–SW direction along its strike on a length 400 km and N–S direction at its centre on a length 60 km, respectively. Both faults are associated with subvertical zones of high electrical conductivity and sensitivity tests suggest that they reach depths of up to 12 km. A sizeable conductor at 50 km depth, which appears consistently in the 2-D sections, could be identified as an inversion artefact caused by a conductor east of the profile. We speculate the high conductivity associated with the off-profile conductor may be related to the detachment of the Trujillo Block. Our results partially support the ‘floating orogen hypothesis’ developed to explain the geodynamic evolution of western Venezuela and they highlight the relevance of the Trujillo Block in this process.

Integrated geophysical investigation techniques for mapping cassava effluent leachate contamination plume, at a dumpsite in Ilero, southwestern Nigeria

The subsurface illuminating strength of integrating Electrical Resistivity (ER) and Frequency Domain Electromagnetic (FDEM) geophysical investigation techniques to evaluate the level of subsurface leachate contamination plume generated by indiscriminate dumping of cassava product processing effluents and wastes around a dumpsite near cassava processing mill at Ilero southwestern Nigeria, has been demonstrated in this study. The lateral spread as well as depth extent of the cassava waste effluent leachate plume was determined from the subsurface resistivity and conductivity models generated from combined ER and FDEM geophysical surveys carried out through eight (8) Electrical Resistivity Tomography (ERT), eight (8) FDEM and (2) Vertical Electrical Sounding (VES) measurement profiles and stations purposively established across the dumpsite.Quality checked, inverted and depth matched ER and FDEM data generated 1D, 2D, and 3D resistivity and conductivity distribution in the form of subsurface logs, sections, constant depth maps and earth model employed to characterize the study area. Electrical resistivity result presents resistivity distribution that range in value between 21 Ωm to 213 Ωm from the topsoil to depths beyond 7.5 m. The FDEM sections and depth maps show conductivity distribution range between 4 mS/m – 286 mS/m across the dump site and provided information up to a depth of 60 m. The VES results generally delineate three (3) georesistivity layers, which include topsoil, weathered and fractured basement layers, occurring at depth between 0.4 – 10.0 m with characteristic resistivity values from 33.5 Ωm – 37.9 Ωm. The 3D resistivity and conductivity models generated by integrating the various results indicate anomalously low resistivity and relatively high conductivity (21 – 30 Ωm; 11 mS/m – 40 mS/m) zone which defines contamination plume in the central part of the cassava effluents and waste dumpsite.This study has through integrated electrical resistivity and frequency domain electromagnetic geophysical methods of investigation highlighted the subsurface contaminating potential of indiscriminating dumping of agricultural processing effluent and wastes, especially of cassava effluent, which has toxic cyanogenicglucosides constituent that is deleterious to the environment.

Identification of subsurface fluid flow using the 2D geoelectric method in Marunda, North Jakarta

Jakarta is the most densely populated province in Indonesia and it will grow over time. This overwhelming population causes a decrease in the quality and supply of groundwater. Brines has been discovered in several areas in Jakarta. Several studies conducted by earth science researchers conclude that brine in Jakarta appears from either seawater intrusion or trapped connate water. This study focuses on the use of the geoelectric method to evaluate the groundwater quality problem in Kelurahan Marunda. Methods used in this study are resistivity, self-potential, and groundwater sampling. Conductivity, Salinity, pH and water table elevation are the parameters used in this study. These methods are done to observe subsurface groundwater quality, fluid flow and how far the seawater infiltrated. Based on the result of groundwater data of 40 wells, high conductivity and high salinity zones are found. High conductivity in this area affected mostly by the saline factor indicated by high salinity and neutral pH. The subsoil has low resistivity values showed by 2D resistivity data. Also, self-potential data displays a North-South groundwater subsurface fluid flow 1, 20 km from the coastline. Altogether, these data indicate seawater intrusion in Kelurahan Marunda, North Jakarta.

Three-Dimensional Reverse Time Migration of Ground-Penetrating Radar Signals

Three-dimensional (3D) ground-penetrating radar (GPR) systems and 3D seismic imaging techniques have been developing fast and evolving rapidly in the last decade. Ray-based migration methods have been successfully applied to processing 3D GPR signals based on the similarity between electromagnetic and seismic waves. However, reverse time migration (RTM) of 3D GPR signals has not been well studied in the past. In this paper, we present a 3D RTM based on Maxwell’s equations for 3D GPR surveys. Migration recovers the true subsurface structure from a distorted and unfocused time profile and suppresses common electromagnetic clutter and noise. RTM based on Maxwell’s equations can consider conductivity directly and compensate for the attenuation within a high-conductivity zone. Compared with 2D RTM, 3D RTM back-propagates both in-line and cross-line signals simultaneously and can include complex 3D permittivity and conductivity models. We have integrated a parallel finite-difference time-domain (FDTD) algorithm based on a hybrid MPI and OpenMP scheme to reduce the computational cost of 3D problems. The 3D RTM experiments on an anomaly of “EM” shape and a realistic sand dune model demonstrate the effective recovery of 3D subsurface structures.

Seismic anisotropy time variations at Mt Etna

SUMMARYThe aim of this paper is to study the temporal variations in the seismic wavefield associated with the stress changes in the dynamic features of the Mt Etna volcanic activity. We used shear wave splitting analysis on a huge data set of local earthquakes, in order to identify changes of the local stress field at Mt Etna during the time interval from 2006 to 2011. This analysis allows us to obtain two parameters: the polarization direction of the fast shear wave (φ) and the time delay of the slow shear wave (Td,time delay between the split shear waves). Orientation of φ generally provides information about the anisotropic symmetry and stress direction whereas Td provide information about the average crack density along the ray path.Based on our findings it is possible to divide Etna Volcano in three different sectors, each one distinguished by typical fast wave polarization direction. We find that the western part of the volcano is controlled by the regional tectonic stress field having a NS and EW directions. Instead, the eastern part of the volcano is mainly controlled by the local volcanic stress, particularly an EW local stress field in the NE sector (Pernicana), and a quasi NS local stress field in the SE sector (Mascalucia, Timpe), where previous studies evidenced: (i) some low-Qp anomaly regions between 0 and about 6 km depth, probably associated with high pore pressure and the intense faulting and (ii) by magnetotelluric surveys, several high conductivity zones, up to 8 km depth, related to a diffuse presence of hydrothermal activity and fluid circulation. Temporal variations in time delay, mostly before the 2008–2009 lateral eruption, can be interpreted as stress accumulation increase with a consequent release of stress due to coalescing of microcracks in the conduit for the eruption of magma.

Influence of the grain size of high explosives on the duration of a high conductivity zone at the detonation

At the detonation of condensed explosives, on the profile of electric conductivity is observed the area of high values, which is usually associated with the chemical reaction zone. The new interpretation of experimental data on the electrical conductivity allows one to diagnose the influence of the grain size on the charge structure and the reaction zone in the whole range of densities investigated. The reliability of the proposed hypotheses are investigated by the methods of statistical analysis. The level of confidence shows the consistency. The results of this paper are useful for the explosion physics, for the industrial production of nanodiamonds, for the miniaturization of explosive devices.

Two-Dimensional Inversion Magnetotelluric Investigation of the Pariangan Geothermal Field, Indonesia

Pariangan geothermal field is located in Tanah Datar District, West Sumatera Province, Indonesia. The structure developed in this region is influenced by a large fault that extends through Sumatera from Banda Aceh to the Gulf Semangko in Lampung and also the pattern of radial faults that follow the development of Complex Marapi Volcanism. This study is aimed at delineating the shallow as well as deeper conductive anomalies related to the geothermal system in the Pariangan area. Dimensionality analysis showed a two-dimensional (2D) behavior for the data, and therefore 2D inversion was performed. The result of magnetotelluric (MT) data processing indicates a low resistivity (<15 Ω.m) distribution at depths of 1300-3000 meter, which is interpreted as the caprock. Reservoir rock is indicated by the medium resistivity (15-93 Ω.m) at depths of 1200-3200 m. Below the reservoir the deep reaching conductive anomaly is interpreted as circulating hot fluids which heat up the fluids in the reservoir due to the subduction process. Type of alteration developed in research area are dominated by argillic type characterized by the presence of illite, kaolinite, montmorillonite, dickite, and halloysite; propylitic type characterized by the presence of chlorite, epidote and, quartz; and phyllic type characterized by the presence of sericite, quartz, and chlorite. Basement rock zone is indicated by the high resistivity (93-1000 Ω.m) at the depths of 1500-6000 m. MT in this study shows a powerful geothermal exploration tools because of its sensitivity to image hot saline fluids as zones of high conductivity.

Electromagnetic studies of the western part of the Ukrainian Shield

Results of synchronous magnetotelluric and magnetovariation researches along profiles Radomyshl—Fastiv and Ruzhin—Skvira conducted in 2015 for studying the deep structure of crust of the western part of the Ukrainian Shield, on purpose of search the zones of metasomatism and the related ore occurrences minerals are given. Tippers for the periods of geomagnetic variations from 20 to 3700 s and curves of apparent resistan-ce from 10 to 10 000 s are received. According to high-quality interpretation of complex tippers and MTZ curves on a profile Radomyshl—Fastiv three local abnormal structu-res are allocated confined to crossing of separate parts of the submeridional faults, such as Vilensky, Kocherivsky and Brusilivsky with the system of sublatitudinal minor faults. The analysis of MTZ curves confirms the non-uniform three-dimensional situation on all the area of research. In the center of Kocherivska sinclinal structure the existence of a high-conductivity zone which roof lies at a depth of 20—50 km is supposed. On a pro-file Ruzhin—Skvira the following anomalies are recognized: the local high-conductivity surface which is situated in the Zvizdal-Zaliska fault zone; the near-surface one which goes deep to the east along the profile and can correspond to the geological structure, namely the Samgorodsky fault of the second order, and it is limited from the west by Ogiyvsky, and from the east by Velikoyerchikivsky deep faults. Anomalies of high electrical conductivity are spatially confined to the known ore-bearing fields — Papirnyanske, Tovstovske and Kocherivske of the rare metal pegmatites and Potashnyanske tungsten ore field. The anomalies allocated spatially coincide with the zones of distribution of metasomatism and metasomatically changed rocks which are promising for endogenic mineralization, namely skarn in the Volynsk megablock; greisens and zones of epi-dotization, quartzitization in Kocherivsky synclinoriums; zones of quartzitization and mik-roklinization of the Zvizdal-Zaliska faults zone; zones of chloritization, mikroklinization, epidotization and hydrothermal change of rocks of the Brusilivska fault zone; zones of a muskovitization, epidotization and quartzitization of the Rosinsky megablock.

Comparative tomography of reverse-slip and strike-slip seismotectonic provinces in the northern South Island, New Zealand

Actively deforming crust and upper mantle around the obliquely convergent Pacific-Australia plate boundary in the northern South Island of New Zealand have been investigated by seismic tomography using data from a temporary c. 50 station network plus GEONET. The Alpine-Wairau Fault (principal component of the plate boundary at the surface) transects the study area, separating the Buller-Nelson (BN) province of active compressional inversion involving steep reverse faulting to the northwest, from the Marlborough fault system (MA) dominated by dextral strike-slip faulting to the southeast. In the course of this study, MA hosted the 2013 Seddon earthquake sequence (M5.9, 6.6) and the 2016 M7.8 Kaikoura earthquake. Active fault structures and present seismicity are associated with a heterogeneous distribution of low-velocity and Vp/Vs anomalies. Elsewhere, there is a general association between crustal seismicity and low-velocity zones along major fault structures within both the MA and BN seismotectonic provinces along which high Vp/Vs anomalies are locally conspicuous. Areas of active crustal seismicity are also generally characterized by high Vp/Vs, for instance the hypocentre and aftershocks of the 2016 M7.8 Kaikoura earthquake overlie a low-velocity region with high Vp/Vs. The coincidence of anomalously low Vp and Vs and anomalously high Vp/Vs with zones of high electrical conductivity defined by a previous MT transect is consistent with the notion that upward migration of overpressured hydrothermal fluid from the subducting slab at depth leads to a heterogeneous distribution of overpressured fluid in and around the base of the crustal seismogenic zone, weakening the overlying crust and promoting seismic rupture along major fault systems. It seems possible that the Association of mid-crustal low-velocity zones with anomalously high Vp/Vs may diagnose rupture preparation zones where frictional strength is being lowered by the build-up of fluid overpressure concurrent with accumulating shear stress, so that eventual fault failure is ‘dual-driven’.

A microseismic-based fracture properties characterization and visualization model for the selection of infill wells in shale reservoirs

Microseismic monitoring is widely applied to detect microseisms touched off by shear slippage on bedding planes or natural fractures in the vicinity of the hydraulic fracture stages being stimulated, characterize full fracture geometry and orientation, fracture complexity and also measure the stimulated reservoir volume (SRV). Microseismic events are recorded by geophones at the surface, near-surface or in monitoring boreholes and their hypocenters are mapped via P and S wave arrival picking and hodogram analysis or seismic imaging technology. Fracturing treatment parameters and events attributes, such as seismic moment, rock rigidity, fluid efficiency, injected fluid volumes, displacement along the slip plane and hypocenter focal mechanism, can be used to measure the fracture geometry and orientation for 3D discrete fracture networks (DFNs) modeling. In the DFNs, every modeled fracture plane shaped by uniformly-spaced point arrays is centered on a microseismic event. All these pointsets are classified to different cells in a geocellular model. Then geocellular cubes with uniform dimension are created in the SRV and event-based fractures are mapped onto each cube. Based on the domain classification methodology, the total intersected fracture polygon area in each SRV cube was calculated for fracture properties (such as fracture intensity, fracture porosity) characterization. Fracture permeability scalar was proposed to capture the unscaled permeability enhancement in 3D geocellular framework. 3D visualization plots would be used to determine the high conductivity zone in the productive SRV, which further helps selecting the optimal position for the infill wells and further enhances the oil and gas recovery.

Atomistic simulations of molten carbonates: Thermodynamic and transport properties of the Li2CO3-Na2CO3-K2CO3 system.

Although molten carbonates only represent, at most, a very minor phase in the Earth's mantle, they are thought to be implied in anomalous high-conductivity zones in its upper part (70-350 km). Besides, the high electrical conductivity of these molten salts is also exploitable in fuel cells. Here, we report quantitative calculations of their properties, over a large range of thermodynamic conditions and chemical compositions, which are a requisite to develop technological devices and to provide a better understanding of a number of geochemical processes. To model molten carbonates by atomistic simulations, we have developed an optimized classical force field based on experimental data of the literature and on the liquid structure issued from ab initio molecular dynamics simulations performed by ourselves. In implementing this force field into a molecular dynamics simulation code, we have evaluated the thermodynamics (equation of state and surface tension), the microscopic liquid structure and the transport properties (diffusion coefficients, electrical conductivity, and viscosity) of molten alkali carbonates (Li2CO3, Na2CO3, K2CO3, and some of their binary and ternary mixtures) from the melting point up to the thermodynamic conditions prevailing in the Earth's upper mantle (∼1100-2100 K, 0-15 GPa). Our results are in very good agreement with the data available in the literature. To our knowledge, a reliable molecular model for molten alkali carbonates covering such a large domain of thermodynamic conditions, chemical compositions, and physicochemical properties has never been published yet.

Magnetotelluric investigations in the southern end of the Cambay basin (near coast), Gujarat, India

Cambay basin is one of the major onshore oil-bearing sedimentary basins of India situated at its western margin in Gujarat state. The region is seismically active and experiences three devastating earthquakes in the past. The region comes under the seismic zone IV and V and necessitates the extensive geophysical studies in for subsurface characteristics and identification of hidden faults in the region for seismic hazard estimation. A magnetotelluric (MT) survey has carried out in the southwestern part of the Cambay basin to identify the sedimentary thickness, the depth of Deccan trap and for identification of West Cambay margin that passes through the region. The MT data, at 13 stations, in the broad frequency range is acquired along an east-west profile with an inter-station spacing of 2–3 km. After processing and analysis of the data, transfer functions in the period band of 0.001–300 s are used for two-dimensional joint inversion. The resultant structure from the 2-D modeling infers the sedimentary thickness of ~0.5 km. A high conductive zone dipping towards east observed in the eastern part of the profile might be due to the West Cambay fault. Basement fracturing at a depth of 2.5–3.0 km at the central portion of the profile might act as a heat exchanger between the deeper geothermal source and nearby hot water spring.

Structural Analyses aiding Identification of Water Conductive Fracture Zones in Crystalline Rock

Development of hydraulic conductive zones in crystalline rock can result from a wide range of geological conditions which include primary structures, post crystalline tectonics, fluid solution and movement within a developing and eroding regolith.Crystalline rock areas mostly have low water resource potential due to inherent extremely low storage and water conductive properties. Therefore, fracture zones of high hydraulic conductivity have an important role in developing groundwater resources that may be distant or where it may be difficult to obtain alternative sources in these areas.Mechanisms for development of open tension or pull-apart fractures in brittle rocks are similar to those involving development of mineralised veins. The same structural analytical techniques can be applied for water bearing structures.Crystalline rock fracture zones can be amenable to rapid recharge through rainfall runoff. They are also significant in that they provide a mechanism for underdrainage through ‘delayed yield’ of surrounding or enclosing low conductive rocks such as saprock/saprolite, pelite and phyllite.In addition to brittle rocks, open tension fracture zones of enhanced hydraulic conductivity may also occur in more fissile pelitic rocks such as slate and phyllite. These conductive zones are often associated with crestal zones of folds, strike deviations produced by conjugate shears and fracture zones discordant with layering and foliation. The development of conjugate joint sets in a region frequently provide a significant basis for this type of fracture analyses.This presentation provides examples of water supplies developed from crystalline rock structures in a range of geological and earth environments.

Structural Analyses aiding Identification of Water Conductive Fracture Zones in Crystalline Rock

Development of hydraulic conductive zones in crystalline rock can result from a wide range of geological conditions which include primary structures, post crystalline tectonics, fluid solution and movement within a developing and eroding regolith.Crystalline rock areas mostly have low water resource potential due to inherent extremely low storage and water conductive properties. Therefore, fracture zones of high hydraulic conductivity have an important role in developing groundwater resources that may be distant or where it may be difficult to obtain alternative sources in these areas.Mechanisms for development of open tension or pull-apart fractures in brittle rocks are similar to those involving development of mineralised veins. The same structural analytical techniques can be applied for water bearing structures.Crystalline rock fracture zones can be amenable to rapid recharge through rainfall runoff. They are also significant in that they provide a mechanism for underdrainage through ‘delayed yield’ of surrounding or enclosing low conductive rocks such as saprock/saprolite, pelite and phyllite.In addition to brittle rocks, open tension fracture zones of enhanced hydraulic conductivity may also occur in more fissile pelitic rocks such as slate and phyllite. These conductive zones are often associated with crestal zones of folds, strike deviations produced by conjugate shears and fracture zones discordant with layering and foliation. The development of conjugate joint sets in a region frequently provide a significant basis for this type of fracture analyses.This presentation provides examples of water supplies developed from crystalline rock structures in a range of geological and earth environments.

An application of hydraulic tomography to a deep coal mine: Combining traditional pumping tests with water inrush incidents

Water inrush incidents threaten the safety of coal mining. Understanding of hydrogeologic parameter distributions is critical for preventing water-related hazards in coal mines. During the deep mining (>1000 m) under the North China Plain, water from water-bearing strata discharges into coal seams through geologic conduits (i.e. water inrush) due to the fractured zone under the floor of working faces. In this study, a water inrush incident was exploited as an active stimulus. A 3D groundwater flow model was built for the eighth member of the Middle Ordovician system in Xingdong coal mine. Using this model and an inverse approach, we first checked if the data from the incident and an independent pumping test carry non-redundant information about the heterogeneity of the mine. Afterward, we combined these datasets to conduct a large-scale (approximately 10 km) hydraulic tomography (HT) analysis. The estimated hydraulic conductivity distribution from the HT analysis is found consistent with the distribution of known geologic faults. That is, a cluster of faults is characterized as a high-conductivity zone. A high conductivity zone is identified at locations close to the water inrush location, which is the high cement consumption zone during the grouting project. Finally, results of this study promote exploiting the water inrush events as a HT survey for mapping geologic structures over a large area.

Magnetotelluric Imaging of the Zhangzhou Basin Geothermal Zone, Southeastern China

The geothermal zone of southeast China, which is one of the country’s known geothermal zones, contains significant natural geothermal resources. To understand the formation of geothermal resources, a magnetotelluric (MT) investigation with a site spacing of 1–2 km was carried out around the Zhangzhou Basin. The recorded MT data were processed by robust time series and remote reference processing techniques. The data analysis results revealed that two-dimensional (2-D) modeling can be used to approximately determine the electrical structure. The joint inversions of TE and TM modes have been performed after distortion decomposition. In the inversion models, a low resistivity cap of 200–800 m thickness was observed, which represented the blanketing sediments composed of Quaternary and volcanic rocks of the late Jurassic period. The presence of high resistivity above a depth of 20 km indicates the granites are widely developed in the upper and middle crust. MT measurements have revealed some deep-seated high conductive zones, which were inferred to be partially melting at depth of 8–17 km, which is likely to be reason behind the formation of higher-temperature hot springs. The results also show that there is a shallower Moho, which indicates that the heat from the upper mantle may have a big contribution to the surface heat flow. Fractures-controlled meteoric fluid circulation is the most likely explanation for the hot springs.

Thermal cloak with adaptive heat source to proactively manipulate temperature field in heat conduction process

Thermal cloaks can thermally hide an object without disturbing background thermal field. The coordinate transformation method for designing conventional thermal cloaks face some challenges that the physical properties of metamaterials are required to be anisotropic and inhomogeneous. Furthermore, the coordinate transformation is not applicable for complex geometrical conditions. In this study, a proactive thermal cloak is proposed. The cloak contains two concentric annular zones: one with high thermal conductivity and another with adaptive heat source. The cloaked zone is surrounded by the high thermal conductivity zone. The high thermal conductivity zone keeps the object in the cloaked zone from thermally being affected by outside zones. The heat source zone adjusts the background thermal field without any distortion. The thermal cloak with an analytical heat source distribution is presented for the 2D and 3D background thermal fields with uniform gradient. The adaptive heat source in the thermal cloak is designed by inverse problem theory of a numerical method for the 2D arbitrary background thermal field. This proactive thermal cloak can avoid the issue of anisotropic physical properties for the conventional thermal cloak designed with coordinate transformation method. The heat source thermal cloak with relatively easy implementation can manipulate temperature field proactively without contact. This thermal cloak is applicable for arbitrary background thermal fields and complex geometrical conditions by a numerical design approach. The proposed thermal cloak opens a new strategy to manipulate the thermal field with adaptive heat source.