Electrical Resistivity Model Research Articles

A Photoconductance Mechanism for Oil Shale Pyrolysis Process Detection

Abstract Kerogen in oil shale plays a crucial part in the shale oil and gas generation. Here, photoconductive measurement was used to evaluate the decomposition process of Huadian oil shale. The photoconductivity of the semi-coke is a clear indicator of different pyrolysis stages, including moisture evaporation, primary pyrolysis of kerogen, decomposition of asphalt monomer, and mineral decomposition. Furthermore, the distribution model of electrical resistance (R) and photoconductance (ΔI) for Huadian oil shale is plotted, indicating an inverse proportion between R and ΔI. We believe that the photoconductive measurement will be a valuable means for the nondestructive characterization of oil shale pyrolysis, which is helpful to optimize the comprehensive utilization of this unconventional resource.

Relationship of the Crustal Structure, Rheology, and Tectonic Dynamics Beneath the Lhasa‐Gangdese Terrane (Southern Tibet) Based on a 3‐D Electrical Model

AbstractThe tectonic dynamics of the Lhasa‐Gangdese terrane, southern Tibet, are still unclear and open questions persist regarding the structure, physical properties, and rheology of the lithosphere. A three‐dimensional electrical resistivity model was generated beneath the Lhasa terrane, 79°−94°E and 28°–33°N, an area of ∼1,500 by ∼600 km, using data from 537 magnetotelluric measurements. To overcome computational challenges, we present an approach in which multiple high‐resolution models from overlapping subregions are combined by means of an error‐weighted averaging scheme to construct a continuous electrical resistivity model. Based on the electrical structure, the rheology of the mid‐lower crust was investigated by constraining the melt fraction, in order to explore controls on dynamic mechanisms from a whole‐system perspective. The models shed light on the vertical and lateral migration of crustal materials, magma transportation, and continental deformation in the Lhasa terrane. The model shows resistive features in the south that may represent the Indian plate, and conductive features above this that may represent the migration of materials beneath the Lhasa terrane, both of which vary substantially along the Indus‐Yarlung Zangbo suture. In the mid‐lower crust, conductive features (with a likely corresponding decrease of the effective viscosity) may be related to underplating, magma reservoirs, mineralization sources, and vertical motion of buoyant materials. A weakened mid‐lower crust has consequences for surface deformation and may have contributed to the formation of (north‐south) rift zones. Furthermore, the inhomogeneous distribution of weakened areas in the mid‐lower crust has implications for the local lateral migration of materials.

The Utilisation of Electrical Resistivity Imaging (ERI) for Geological Structures Mapping in Rock Mass: A Review

Electrical Resistivity Imaging (ERI) is an in-situ geophysical method widely used in environmental, engineering and hydrogeological explorations due to cost, time, and data coverage efficiency. Traditionally, geotechnical parameters such as discontinuities properties are obtained from rock samples acquired from a borehole. However, it only provides a single information point, costly and time-consuming. Thus, an approach using electrical resistivity to detect the presence of geological structure in a rock mass is an alternative method that can be applied. Discontinuities in rock mass include joints, bedding planes, blasting cracks, fractures, faults, and folds. This paper aims to present the utilisation of geoelectrical resistivity imaging for geological structures mapping in rock mass based on the review from previous research. The Electrical Resistivity Imaging (ERI) method is an effective tool to obtain structural differentiation of geological medium by interpreting 2D and even 3D electrical resistivity models. Electrical Resistivity Imaging (ERI) is an automated data acquisition system, inversion codes, non-invasive and user-friendly. The raw data received from data acquisition was analysed using Res2DINV software. The data inversion was done by applying the robust method and finite element grid to accommodate the steep topography. The data interpretation included numerical modelling to assess the suitability of all used electrode arrays in relation to the geological setting.

Magnetotelluric Evidence for Lithospheric Alteration Beneath the Wuyi‐Yunkai Orogen: Implications for Thermal Structure of South China

AbstractThe Wuyi‐Yunkai Orogen experienced a polyphase tectonomagmatism and is a key region for deciphering the alteration and thermal structure of the South China Block lithosphere. Herein, an electrical resistivity model of the lithosphere is presented via the three‐dimensional inversion of broadband (0.003–3600 s) magnetotelluric (MT) data collected along a 380‐km‐long profile comprising 62 MT sites across the Wuyi‐Yunkai Orogen, and the robustness of this model is critically evaluated through a series of sensitivity tests. The resistivity model reveals that the upper crust of the Cathaysia Block and the Wuyi‐Yunkai Orogen is dominated by high‐resistivity sedimentary cover interposed with low‐resistivity features, mainly along fault zones. High‐resistivity bodies and strong conductors in the upper crust are interpreted as magmatic rocks and tectonic mélanges, respectively. Another feature of this resistivity model is the presence of zones featuring enhanced electrical conductivity (<30 Ωm) extending from the lower crust to the upper mantle beneath the Wuyi‐Yunkai Orogen. The conductors in the lower crust are attributed to saline fluids from either the dehydration of the subducting Paleo‐Pacific slab or the regional metamorphism‐induced dehydration of sandy argillaceous rocks. In contrast, the conductors in the upper mantle are attributed to 4%–7% partial melt, which corresponds to the analyses of mantle xenoliths in South China. These conductors in the upper crust and upper mantle supply volatiles and heat to shallow geothermal systems. This work ultimately shows that the lithospheric thinning of South China is controlled mainly by mantle upwelling caused by the retreat of the subducting Paleo‐Pacific slab.

Identification of hyporheic extent and functional zonation during seasonal streamflow recession by unsupervised clustering of time‐lapse electrical resistivity models

AbstractHyporheic exchange influences hydrologic transport and water quality through transient storage, which extends solute transit time, and leads to mixing of surface water and groundwater. Despite its importance, estimating the extent and spatiotemporal variability of the hyporheic zone remains challenging due to limitations in assessing the subsurface with discrete point‐scale sampling. Analysis of time‐lapse electrical resistivity (ER) data from tracer studies has shown potential to ameliorate such limitations. However, its utility in objectively delimiting hyporheic extent and quantifying changes in surface‐groundwater exchange has been impeded by reliance on qualitative analysis of hyporheic extent or the use of a priori assumptions about data quality and signal strength. This study applies a novel unsupervised clustering method to time‐lapse ER models derived from a benchmark dataset collected throughout baseflow recession in a mountain stream. We demonstrate that unsupervised clustering of inverted ER model time series can delimit hyporheic extent by distinguishing solute transport signals from noisy background inversions and identify functional zones defined by unique transport characteristics. We found that the structure of these zones was stable even as discharge changed by an order of magnitude, likely due to morphological constraints in this steep, narrow valley. Compared to traditional methods utilizing a priori thresholds to delimit hyporheic extent, clustering is robust to unintentional variations in tracer breakthrough curves that are typical of field‐based studies. Therefore, clustering of inverted ER models represents a more robust and data‐driven functional zonation representation of hyporheic exchange than has been possible with point‐scale sampling or transport modelling, which usually assumes a single well‐mixed hyporheic zone.

Effect of Ag and Cu addition on the strength and electrical conductivity of Al-Mg-Si alloys using conventional and modified thermomechanical treatments

The effect of adding Ag and Cu on the strength and electrical conductivity of Al-Mg-Si conductor alloys was investigated using conventional and modified thermomechanical treatments. In the conventional thermomechanical treatment, the addition of Ag and Cu moderately increased the strength from 296 MPa to 305–316 MPa above the minimum required electrical conductivity (52.5% IACS) compared to that of the base alloy. However, the modification of the thermomechanical treatment could maximize the efficiency of Ag and Cu addition at strengths above 52.5% IACS, exhibiting that the strength was increased from 317 MPa to 341–348 MPa with the Ag and Cu additions. All alloys under the modified thermomechanical treatment (MTMT) showed a superior strength and electrical conductivity compared to their counterparts under the conventional thermomechanical treatment (CTMT), resulting in a wider window in the high end of strength and electrical conductivity. In addition, MTMT led to a shorter post-aging time to reach the minimum required EC, compared to CTMT. The precipitate characteristics under both thermomechanical treatment conditions were analyzed and quantified using differential scanning calorimetry and transmission electron microscopy (TEM). The TEM results revealed that the alloys under MTMT had a higher precipitate number density by more than three times compared to their counterparts under CTMT, leading to the higher strength levels in the MTMT alloys. Strength and electrical resistivity models were then applied to understand the multiple contributions of the main strengthening mechanisms and microstructure features to the mechanical strength and electrical conductivity. • Modified thermomechanical treatment is proposed to enhance both strength and electrical conductivity (EC). • The effects of Ag and Cu additions on the strength and EC in Al-Mg-Si conductor alloys are studied. • The efficiency of the Ag and Cu additions is maximized using the modified thermomechanical treatment in terms of strength and EC. • The strength and electrical resistivity models are applied.

Three‐Dimensional Electrical Structure and Magma System of the Monogenetic Longgang Volcanic Field, Northeast China, Inferred From Broadband Magnetotelluric Data

AbstractThe Longgang volcanic field (LVF) is one of the largest intraplate monogenetic volcanic regions in China, and eruption lasted from the early Pleistocene to the Holocene. Previous research shows that the LVF is not only experiencing rapid surface uplift but also significant seismic activity. The magmatic system under the LVF poses a hazard of potential eruption. The three‐dimensional electrical resistivity model developed by magnetotelluric data shows that the upper crust of the LVF and the surrounding areas hosts a high‐resistivity body composed of volcanic rocks produced by massive eruptions during past volcanic episodes. There are two main high‐conductivity structures below the depth of 10 km in the southwest and northeast of the LVF. The two structures merge in the lower crust and extend to the mantle. We interpret these high‐conductivity structures to be magmatic channels (the resistivity of C1 is 20–50 and C2 is 5–20 Ωm). Magmatic channel upwelling along the C1 may have caused the eruption of the Jinlongdingzi volcano 1,700 years ago. The C2 magmatic channel in the northeast of the LVF is larger and lower resistivity than C1. The modern surface uplift and seismicity in the LVF is a result of upwelling and intrusion along C2 magmatic channel. The Hunjiang fault passing through the LVF may also influence the upwelling of material along the C2 magmatic channel, posing a hazard of future eruption in the LVF. The high‐conductivity structures in the LVF pass through the Moho and extend to the upper mantle and are connected from the top to bottom. Combined with geochemical data, we speculate that the magmatic system in the LVF may directly come from the upper mantle and the magma has experienced rapid ascent with limited crustal internal evolution.

Identification of Different Shallow Foundations Using 3D Electrical Resistivity Modeling

The electrical resistivity method has been successfully used to detect shallow buried foundations, almost, by using 2D electrode arrays. Basic geometry foundations (e.g., buried walls) have been investigated, although, more complicated foundation designs (e.g., stepped footing, pile group with a pile cap) are widely used in the construction industry. Investigation of these complicated foundation types, and engaging 3D surveys, therefore, are required. Multiple 3D electrical resistivity forward modeling was used to simulate different foundations (isolated simple footing, isolated stepped footing, combined simple footings, and pile group with a pile cap). The generated data sets then inverted using a robust inversion algorithm where RES3DINVx64 was used to perform the inversion process for the 3D models. The results from the 3D inverse modeling, suggest the pole-dipole and dipole-dipole arrays for all the investigated foundations.

Gravity and electrical resistivity analysis of deep and shallow structures related to aquifers within the Jeffara Plain, southeast Tunisia

The aquifers under the Jeffara Plain in southeastern Tunisia is a complex aquifer system consisting of interconnected shallow and deep aquifers within Triassic and younger sediments. The extent of the aquifers is only roughly known, so a gravity and electrical resistivity analysis was undertaken to aid for determining the aquifers extent. The gravity analysis consisted of creating a residual gravity anomaly map, a power spectrum analysis to determine the depth to density sources and a 3D Euler deconvolution analysis to locate lineaments and the depth of density sources. The gravity analysis was used to infer the location and depth of faults and thicker portions of the aquifer containing sediments The electrical resistivity survey was used to characterize the geometry and the depth of deep and shallow aquifers surrounding Medenine city. The residual gravity anomaly map identified a series of northwest-trending gravity minima related to grabens. The Euler deconvolution determined faults can be classified into deep faults (˃ 2.5 km depth) that these associated with the Medenine fault and nearly determined offshoots that trend north-northeast, shallow (0.5–1.0 km) and near surface faults (<0.5 km). The shallow and the near-surface faults involve Upper Cretaceous and younger sediments and trend in a variety of directions. The electrical resistivity models indicate that the shallow aquifers are approximately 20 m thick and the deep aquifer is found below 25 m in depth and is at least 30 m thick. The shallow aquifers were found on all four models but the deep aquifer was found only on two profiles. The location of both the shallow and deep aquifers were affected by faults inferred by the electrical resistivity data and these faults were correlated with lineaments determined by the gravity analysis. This shows that the shallow/near surface faults are important conduits between the shallow and deep aquifers. The most important fault was the Medenine and its newly deduced offshoots as the electrical resistivity models indicate that these faults act as a barrier for the deep aquifer. Based on both the gravity analysis and the electrical resistivity models, the extent of the deep aquifer can be extended further to the east than was previously known.

Investigation of the electrical resistivity structure of the subsurface at Mogod valley in central Mongolia: Insight is using 1D Magnetotelluric inversion

In this paper, we report a preliminary result of the Magnetotelluric investigation of the Mogod area. The Mogod region is one of the most prominent fields for geophysical study since the region includes young and active faults and geothermal activities. We conducted magnetotelluric measurements at 20 sites during geophysical field seasons in 2018-2021 as a pilot survey to understand data property and the electromagnetic noise level for the detailed electromagnetic studies. During the fieldwork, we used Lemi Magnetotelluric instruments and measured all three orthogonal components of the magnetic field and the horizontal components of the electric field. For the data processing, we used Matlab code by using the M-estimate regression method, and estimated the magnetotelluric transfer function with a lownoise level. The electrical resistivity model of the subsurface of survey layout shows us the existing resistivity anomalies at shallow-depth, and thickness of the upper crust approximately 11-17 km. Here, suggest that the thickness of the upper crust is 17 km and crust is 40 km with local magnetotelluric measurements. Additionally, the electric conductor appears in the southwest of Mogod region, we interpret that conductor play as a source of geological activity of Mogod region, and it might be the signature of a remanent fluid.

Investigation of the electrical resistivity structure of the subsurface at Mogod valley in central Mongolia: Insight is using 1D Magnetotelluric inversion

In this paper, we report a preliminary result of the Magnetotelluric investigation of the Mogod area. The Mogod region is one of the most prominent fields for geophysical study since the region includes young and active faults and geothermal activities. We conducted magnetotelluric measurements at 20 sites during geophysical field seasons in 2018-2021 as a pilot survey to understand data property and the electromagnetic noise level for the detailed electromagnetic studies. During the fieldwork, we used Lemi Magnetotelluric instruments and measured all three orthogonal components of the magnetic field and the horizontal components of the electric field. For the data processing, we used Matlab code by using the M-estimate regression method, and estimated the magnetotelluric transfer function with a lownoise level. The electrical resistivity model of the subsurface of survey layout shows us the existing resistivity anomalies at shallow-depth, and thickness of the upper crust approximately 11-17 km. Here, suggest that the thickness of the upper crust is 17 km and crust is 40 km with local magnetotelluric measurements. Additionally, the electric conductor appears in the southwest of Mogod region, we interpret that conductor play as a source of geological activity of Mogod region, and it might be the signature of a remanent fluid.

Physical modeling of electrometric control of leaks from the pregnant solution pond

The search for leaks from various hydraulic structures is a topical task of electrometry. Pregnant solution pond is one of the objects of electrometric control. They accumulate gold-enriched solutions. Identification of a breach in the waterproofing layer of a pond is possible by the method of electrical resistivity tomography with the measurement of induced polarization. Physical simulations were carried out to determine the nature of the electrical anomalies caused by the breach. A small plastic water tank imitated a solution pond. A hole was made in the bottom of the small tank, it provided a hydraulic connection with the large tank. The measurements were performed with the Skla-64 equipment, and the two-dimensional data inversion was carried out using the Res2DInv program. As a result, it was found that the place of leakage is allocated by an anomaly of low electrical resistivity and an intense anomaly of normalized chargeability. However, the 2D electrical resistivity model is complicated by inversion artifacts. The normalized chargeability anomaly is local and accurately marks the location of the leak in the bottom of the tank. It is proposed to use a complex analysis of electrical resistivity and normalized chargeability for electrometric monitoring of leaks from pregnant solution pond and other hydraulic structures.

Multivariate distribution models of soil electrical resistivity

Soil electrical resistivity is an important parameter in geotechnical engineering. In this paper, a multivariate distribution model is used to predict soil electrical resistivity. The Box-Cox method was used to transform the soil parameters, which were then analysed by a correlation matrix. Multivariate distribution models with different input parameters were established, verified and analysed, and compared with conventional empirical models. The results show that the predictive accuracy of the multivariate distribution models was improved significantly by increasing the number of parameters. The correlation coefficient (R2) of the calibration data increased from 0.05 to 0.88, and that of the validation data increased from 0.06 to 0.83. The model with the best predictive accuracy was the RE−{G, F, Sr} model (R2 = 0.87, E(ε) = 1.22, COV(ε) = 0.98). The predictive accuracy of the multivariate distribution model was obviously higher than that of the conventional empirical model. The multivariate distribution model is an effective and simple way to predict soil electrical resistivity. The proposed model exhibits good performance using limited electrical resistivity data from frozen soils.

Magnetotelluric imaging of the shallow-seated magma reservoir beneath the Karadağ stratovolcano, Central Anatolia, Turkey

The central Anatolian Volcanic Province encompasses many volcanoes elongated in a northeast-southwest direction. Karadağ is one of the dormant Quaternary stratovolcanoes of the region at the southern end of the province. We acquired broadband magnetotelluric (MT) data in the period range 0.0001–251 s at 124 locations to obtain a three-dimensional electrical resistivity model to identify the associated magmatic-hydrothermal system beneath the Karadağ stratovolcano. The resistivity model provides evidence for low resistivity anomalies that include (1) a near-surface localised low resistivity (~ 20 Ωm) zone situated directly beneath the crater centre that is interpreted to be lacustrine sediments of an extinct crater lake, (2) a shallow low resistivity (~ 10 Ωm) zone of probable hydrothermal alteration in the eastern part of the stratovolcano and (3) a deep and large zone of low resistivity (<10 Ωm) attributed to a shallow-seated magma reservoir at a depth of 3 to 7 km beneath the volcanic edifice. A few hundred meters thick resistive surface layer corresponds to the Karadağ adakitic volcanics (i.e., andesites and dacites), and a resistive basement representing Precambrian to Mesozoic high- and medium-grade metamorphic rocks on the flanks is observed in the resistivity model.

Lithospheric electrical structure and its implications for the evolution of the middle Qinling Orogenic Belt, Central China: Constraints from 3-D magnetotelluric imaging

The Qinling Orogenic Belt is located at the central part of the China Central Orogenic Belt and links the Qilian and Kunlun Orogenic Belts to the west with the Dabie-Sulu Orogenic Belt to the east, which is sandwiched between the South China Block and North China Block. There have been several geodynamic models developed to explain the evolution process of the Qinling Orogenic Belt, but they remain controversial. The magnetotelluric (MT) method can study subsurface electrical structures. In order to have a better understanding of the tectonic evolution of the Qinling Orogenic Belt, a study of broadband and long period MT profile across the middle Qinling Orogenic Belt is carried out. The MT profile starts from the northeastern margin of the Sichuan basin, crosses the Qinling, and finally reaches the Weihe basin at about 108.5°E. Based on data analysis results, we have finally obtained a lithospheric electrical resistivity model of the middle Qinling Orogenic Belt through three-dimensional (3-D) inversion of magnetotelluric data. The MT result reveals that the Sichuan and Weihe basins may have remnants of the ancient craton basement in our study area. The electrical structure characteristics of the South Qinling Belt and North Qinling Belt are obviously different, the South Qinling Belt is relatively low resistivity, while the North Qinling Belt is relatively high resistivity. This may indicate that the Southern Qinling Belt is affected by the later strike slip extrusion and the Northern Qinling Belt is a relatively stable block. The lithospheric mantle of middle Qinling Orogenic Belt is characterized by overall high resistivity, which may indicate that the lateral extrusion effect of the Tibetan Plateau material is negligible in this region.

Controls on the metallogenesis of the Lhasa–Mozugongka district, Gangdese Belt, Tibetan Plateau: Constraints on melt distribution and viscosity from the 3-D electrical structure of the lithosphere

Some of the largest and most significant Miocene porphyry copper systems in China are within the Gangdese metallogenic belt on the southern Tibetan Plateau. It has been recognized that the crustal architecture and rheology, derived from regional tectonic events, has direct implications for the evolution and transport of fluids and magmas, and thus for the metallogenesis and prospectivity. Using data from a magnetetolluric array, which intersects the Lhasa–Mozugongka district of the Gangdese metal belt, a 3-D electrical resistivity model was generated, with the goal of investigating the tectonic and rheological controls on the magmatic mineral system. The lithospheric temperature distribution was estimated by applying the Arrhenius equation to conductivity profiles generated from 1-D Monte-Carlo models of long-period magnetotelluric data. The conductivity of partial melts in the lower and middle crust (30–60 km depth) was estimated for local conditions by applying the experimentally-derived equation of X. Guo et al. (2018). Subsequently, we estimated the melt fraction required to explain the observed bulk resistivity in each part of the study area. Variations in the effective viscosity of the lower and middle crust were constrained by the electrical resistivity model by applying the empirical relation of Liu and Hasterock (2016). Beneath the Miocene Cu–Mo deposits in the Lhasa terrane, conductive features in the lower and middle crust are attributed to partial melt fractions of more than 5% and viscosity reductions of 1–2 orders of magnitude. These conductive features may represent the signatures of (ore-controlling) melt/fluid migration channels and deeper melt/fluid source regions in the form of extensive crustal reservoirs of partial melt. Based on the interpretations of the geophysical model, and other available geological and geochemical evidence, a model of the metallogenic dynamics of the Miocene porphyry Cu–Mo deposits is proposed. Overall, the study highlights the applicability of electromagnetic geophysical methods to reliably link resistivity structures to melt/fluid transport channels and sources within a mineral system and supports the hypothesis that crustal rheology exerts a major control on the distribution of ore deposits.

Evidence for the Superposition of Tectonic Systems in the Northern Songliao Block, NE China, Revealed by a 3‐D Electrical Resistivity Model

AbstractThe creation and evolution of the Songliao Block, Northeast China, is believed to be related to the closure of the Paleo‐Asian and Mongol‐Okhotsk oceans, and to the subduction of the Paleo‐Pacific Ocean. Geochemical and geophysical data indicate a complex tectonic history that may have left signatures of the superposition of separate tectonic events. However, the relationship between the current lithospheric structure of the Songliao Block and those tectonic events is not clear. In order to shed light on this question, a three‐dimensional electrical resistivity model of the crust and mantle was generated from 138 magnetotelluric sites. The results show a heterogenous lithosphere with anomalous low‐resistivity zones (∼10 Ω·m). The position of upper‐crustal features (&lt;10 km) correlates with a network of fault systems and rift basins. Based on estimates of high crustal temperatures, mid‐lower crustal features (15–35 km), some of which appear near seismic reflectors, are attributed to partial melts (∼5%) containing moderate‐high water contents (4.5 wt. %). A deep (&gt;45 km) feature is interpreted as an asthenospheric upwelling near the center of the Songliao Block, where seismic evidence indicates a thin lithosphere. It is proposed that the collision, convergence, and suturing of blocks caused by the closure of the Paleo‐Asian Ocean and the bidirectional convergence between the Mongol‐Okhotsk and Paleo‐Pacific Ocean may have produced weak tectonic zones throughout the lithosphere. They provided a structural basis for the later upward movement of fluids and melt, likely due to hydrous upwellings caused by the subduction of the Paleo‐Pacific system.

Three-dimensional crustal and upper-mantle resistivity structure of Alberta, Canada: implications for Precambrian tectonics

SUMMARY This paper describes the first detailed 3-D study of the Alberta basement using the magnetotelluric (MT) method. Long-period MT data were used to generate a 3-D electrical resistivity model of the crust and upper mantle beneath Alberta. The Western Canada Sedimentary Basin was imaged as a low-resistivity layer. A number of crustal and upper-mantle conductors were imaged and include: (1) the Red Deer conductor, (2) the Kiskatinaw conductor, (3) a conductor coincident with the Kimiwan oxygen isotope anomaly, (4) the southern Alberta–British Columbia conductor, (5) the Loverna block conductor and (6) a conductor beneath the Birch Mountain kimberlite field. Conductors (3) and (6) are newly identified in this study. All of these conductors can be related to past tectonic events associated with the assembly of Laurentia and subsequent kimberlite magmatism. The depth of the lithosphere–asthenosphere boundary across Alberta varies from 150 to 300 km as defined from the 100 Ω m contour. Furthermore, the Snowbird tectonic zone in Alberta is characterized by a thick, resistive lithosphere. Similarly, the diamondiferous Buffalo Head Hills kimberlite field is imaged with a thick, resistive lithosphere, both may indicate depletion. In contrast, the Birch Mountain kimberlite field is underlain by a pronounced conductor that extends through the lithosphere and may be the result of metasomatism.

Multi-objective design optimization for graphite-based nanomaterials reinforced cementitious composites: A data-driven method with machine learning and NSGA-Ⅱ

Graphite-based nanomaterials (GNs) are promising conductive fillers for producing highly effective electrically conductive cementitious composites (ECCC) and promoting non-destructive structural health monitoring (SHM) methods. Since acceptable mechanical strength and electrical resistivity are both required, the design of GN-reinforced cementitious composites (GNRCC) is a complicated multi-objective optimization problem (MOOP). The present study proposes a comprehensive data-driven method to address this multi-objective design optimization (MODO) issue for GNRCC using machine learning (ML) techniques and non-dominated sorting genetic algorithm (NSGA-Ⅱ). First, prediction models of uniaxial compressive strength (UCS) and electrical resistivity (ER) of GNRCC are established by Bayesian-tuned XGBoost with prepared experimental datasets. The results show that they have excellent performance in predicting both properties with high R2 (0.95 and 0.92, 0.99 and 0.98) and low mean absolute error (MAE) scores (1.24 and 3.44, 0.15 and 0.22). The influence of critical features on GNRCC’s properties are quantified by ML theories. This helps determine the variables to be optimized and define their constraints for the MODO. Finally, the MODO program is developed on the basis of NSGA-Ⅱ. It optimizes GNRCC’s properties of UCS and ER simultaneously with the proposed prediction models as objective functions. It successfully achieves a set of Pareto solutions, which can facilitate appropriate parameters selections for the GNRCC design.

Geophysical imaging of the Yellowstone hydrothermal plumbing system.

The nature of Yellowstone National Park's plumbing system linking deep thermal fluids to its legendary thermal features is virtually unknown. The prevailing concepts of Yellowstone hydrology and chemistry are that fluids reside in reservoirs with unknown geometries, flow laterally from distal sources and emerge at the edges of lava flows1-4. Here we present a high-resolution synoptic view of pathways of the Yellowstone hydrothermal system derived from electrical resistivity and magnetic susceptibility models of airborne geophysical data5,6. Groundwater and thermal fluids containing appreciable total dissolved solids significantly reduce resistivities of porous volcanic rocks and are differentiated by their resistivity signatures7. Clay sequences mapped in thermal areas8,9 and boreholes10 typically form at depths of less than 1,000 metres over fault-controlled thermal fluid and/or gas conduits11-14. We show that most thermal features are located above high-flux conduits along buried faults capped with clay that has low resistivity and low susceptibility. Shallow subhorizontal pathways feed groundwater into basins that mixes with thermal fluids from vertical conduits. These mixed fluids emerge at the surface, controlled by surficial permeability, and flow outwards along deeper brecciated layers. These outflows, continuing between the geyser basins, mix with local groundwater and thermal fluids to produce the observed geochemical signatures. Our high-fidelity images inform geochemical and groundwater models for hydrothermal systems worldwide.