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The basin environment is a widely studied subject in both geology and geophysics for its economic significance in energy and mineral explorations. However, the estimation of the basement depth is often a challenging task given the complexity of the basement relief and lateral physical property change. Previous works simplify the problem by only inverting for the depth to the basement, and more recent studies have suggested the need to incorporate the variation of physical properties to improve basement structure imaging. In this study, we develop an inversion method with the associated workflow to simultaneously recover both the depth to a magnetic basement and a laterally varying magnetic susceptibility in the basement rock. To achieve this, we employ a set of constraints on the inverse problem. Particularly, both the recovered susceptibility and basement depth models are bounded below a possible maximum value, and the depth model is guided by a few depth points obtained from the resistivity models that are obtained from the one‐dimensional blocky inversions of magnetotelluric (MT) data. In addition, we apply the fuzzy C‐means (FCM) clustering to the susceptibility model during the inversion and use the inverted cluster centers to differentiate for different geological units in the basement. To show the effectiveness of our work, we compare the existing approaches and our method using two test inversions on one synthetic model resembling the basin–basement environment before demonstrating our method on a field data example with magnetic data collected by the U.S. Geological Survey (USGS) over the Illinois Basin. Our results show improved recovery in both basement relief and susceptibility in the basement rock, and inversion with field data is able to identify three different susceptibility zones in basement rock below the Illinois Basin. [ABSTRACT FROM AUTHOR]

The deformation mechanisms of the Tianshan orogenic belt (TOB) are one of the most important unresolved issues in the collision of the Indian and Eurasian plates. To better understand the lithospheric deformation of the eastern Tianshan orogenic belt, we combined the S-wave tomography and gravity data to develop a three-dimensional (3D) density model of the crust and upper mantle beneath the eastern Tianshan area. Results show that the crust of the eastern Tianshan is mainly characterized by positive density anomalies, revealing widespread subduction-related magmatism during the Paleozoic. We however have also observed extensive low-density anomalies beneath the eastern Tianshan at depths deeper than ∼100 km, which is likely linked to a relatively hot mantle. The most fundamental differences of the lithosphere within the eastern Tianshan occur in the uppermost mantle. The uppermost mantle layers in the Bogda Shan and Harlik Shan are relatively dense. This is likely associated with an eclogite body in the uppermost mantle. The most significant negative anomaly of the uppermost mantle is however found in the Jueluotage tectonic belt and the central Tianshan Block and is possibly associated with depleted mantle material. We suggest that these differences related to compositional changes may control the strength of the lithospheric mantle and have affected the uplift of the northern and southern segments of the eastern Tianshan after the Permian. [ABSTRACT FROM AUTHOR]

Walkaway vertical seismic profiling (WVSP) is known for its high level of credibility in obtaining the relationship between first-arrival traveltime and detector depth through first-arrival picking. This relationship can be utilized for seismic velocity model inversion to improve velocity model accuracy and rationality. Here, we present a WVSP first-arrival velocity model with velocity structure constraints, by utilizing layer and fault data interpreted by ground seismic structure technique. We constructed a geological structure and layer sequence models based on sedimentary patterns to obtain complex velocity structures. Furthermore, we introduced a smooth regularization term based on the velocity structure into the inversion model to enhance its consistency with geological laws and compensate for the reduced inversion accuracy owing to the regularization term based on flat structures. This approach addressed the limitations of the regularization term based on flat structures, resulting in more accurate and reliable inversion results. Through simulation analysis, the proposed method realized the WVSP first-arrival velocity inversion, with results being closer to those of the real velocity model.

Density perturbations in the subsurface are the main driver of mantle convection and can contribute to lithospheric deformation. However, in many places the density structure in the subsurface is poorly constrained. Most geodynamic models rely on simplified equations of state or use linear seismic velocity perturbations to density conversions. In this study, we investigate the density structure beneath the Rungwe Volcanic Province (RVP), which is the southernmost volcanic center in the Western Branch of the East African Rift (EAR). We use shear-wave velocity perturbations (dlnvs) as a reference model to perform constrained inversions of satellite gravity data centered on the RVP. We use the code jif3D with a dlnvs-density coupling criterion based on mutual information to generate a 3D density model beneath the RVP up to a depth of 660 km. Our results reveal a conspicuous negative density anomaly (∼−200 kg/m3) in the sublithospheric mantle (at depths ranging from ∼100 km to ∼250 km) beneath the central part of the Malawi Rift extending to the west, beneath the Niassa Craton, coincident with locations with positive shear-wave velocity perturbations (+7%). We calculate a 3D model of the velocity-to-density conversion factor (f) and find negative f-values beneath the Niassa Craton which suggests the observed negative density anomaly is mostly due to compositional variations. Apart from the Niassa Craton, there are generally positive f-values in the study area, which suggest dominance of temperature control on the density structure. Although the RVP generally shows negative density anomalies and positive f-values, at shallow depths (

Mine roof water (water in the overlying aquifers of coal seam) seriously threatens the safe production of coal mines in the Ordos Basin in China. Transient electromagnetic (TEM) and seismic methods are the two key methods of mine roof water detection. To exploit the advantage of each method, the seismic-constrained TEM method is proposed. First, the seismic-constrained TEM inversion algorithm was constructed by adding a cross-gradient function to the pseudo-2D TEM inversion algorithm. The cross-gradient function makes the structures of the TEM and seismic models consistent in inversion. To match the seismic and TEM model grids, the interpolation of the seismic impedance model was proposed. Then, the proposed algorithm was successfully used in the Maiduoshan coal mine in the Ordos Basin. Data acquisition, seismic-constrained TEM inversion and interpretation were carried out. Seventeen boreholes were drilled to verify the interpretation results, and the drilling results are consistent with the detection results. Finally, the seismic-constrained and single TEM methods were compared. Results show that the seismic-constrained TEM method is superior to the single TEM method. The structural consistency of the resistivity and seismic impedance models increases in the seismic-constrained TEM inversion and decreases in the single TEM inversion. Seismic-constrained TEM inversion can add the stratigraphic structure information provided by the seismic method to the TEM inversion, thereby improving the inversion results. [ABSTRACT FROM AUTHOR]

The seismic reflection of volcanic reservoir in deep basin is disorderly due to the influence of energy shielding, which makes the exploration of volcanic reservoir very difficult. Aimed at the complex inner structure of deep volcanic reservoir with multi-phase superposition, the optimal offset, time-frequency electromagnetic acquisition technology of the excitation period window, time-frequency electromagnetic well seismic joint modeling inversion and electrical variation rhythm coding volcanic period interpretation technology are studied, which effectively improved the depth resolution and the recognition ability of the method. The research and application effect in LD area of Bohai Bay Basin are obvious. The results show that the volcanic eruptions of the third member of Shahejie Formation in the Red Star tectonic belt show the characteristics of "two strong three weak" of "weak-strong-strong-weak-weak" from bottom to top. Two volcanic eruption mechanisms are developed, which jointly control the distribution of volcanic reservoir facies in five periods. In Taoyuan structural belt, the volcanic eruption intensity of each stage of the third member of the Shahejie Formation is significantly weakened, and only one volcanic eruption mechanism is developed. Except for the relatively large distribution range of volcanic reservoir facies in stage 3, the volcanic rocks in other stages are mainly confined to the crater, mainly in eruption facies, and their scale is significantly reduced. The follow-up drilling results confirmed that the distribution of volcanic reservoir revealed by time-frequency electromagnetic was correct, which provided strong support for the large oil and gas discovery in this area and provided a successful example and technical methods for the detection of similar complex targets.

In this paper, an improved particle swarm optimization technique known as elitist-mutated particle swarm optimization (EMPSO) was applied in the 2D electrical resistivity imaging, a complex and highly nonlinear optimization problem. The EMPSO enables better exploration of the search space, by replacing particles with a worse performance by the best particle of the swarm mutated in random positions. Nevertheless, this technique, as any other based on a population of models, costs much computation time in solving optimization problems with a large number of unknown parameters. We addressed this problem by developing a parallel version of the EMPSO that supports pure MPI and hybrid MPI-OpenMP modes, and we named as parallel elitist-mutated PSO (PEMPSO). The solution to the inverse problem is based on minimizing an objective function with a regularization term to create a mathematically stable solution. Total variation and global smoothness regularizations were used in the inversion of synthetic data obtained from simple models and a set of real data of a highly complex geological/geotechnical nature. By virtue of the features of the synthetic models and the geology of the local where the data were acquired, the inversions with total variation regularization provided the best outcomes. Additionally, we have improved the execution time significantly with our parallel solution (the pure MPI model turned out to be better than the hybrid model) in comparison with the sequential version. Cumulative frequency distribution of errors between modeled and observed apparent resistivity data for all experiments was used to validate the PEMPSO technique for estimating resistivity. [ABSTRACT FROM AUTHOR]

We develop a novel gravity inversion algorithm in spherical coordinates based on adaptive inversion mesh refinement and multiphysical parameter constraints. The inversion mesh is discretized into tesseroids (spherical prisms) to take the curvature of the Earth into account. To reduce the number of unknowns and computational cost, the inversion mesh is adaptively refined according to the spatial variation of parameters at each iteration. Wavelet compression is used to further reduce the computational requirement. Besides, to alleviate the nonuniqueness of inversion, the algorithm is capable of incorporating a priori models from other geophysical methods via cross‐gradient coupling and/or direct parameter coupling. For cross‐gradient coupling, the vector product of spatial gradients of two model parameters is included in the objective function. For direct parameter coupling, an a priori model is converted to a density model using the relation between two physical properties, which is then used as the initial and reference model in the inversion. A synthetic example is presented to demonstrate the effectiveness of our inversion method. Finally, we invert the gravity data over the Tibetan Plateau to obtain the density variations in the upper mantle, with a global S wave tomographic model used as a constraint. The inversion model shows that the mantle lithosphere beneath the Himalayan collision zone varies from west to east. Low‐density anomalies are observed beneath the southern and the northern Tibetan Plateau, which are consistent with published low‐velocity anomalies and magmatism distributions, possibly indicating two asthenospheric upwellings. Plain Language Summary: Earth's gravity, following Newton's law of universal gravitation, is sensitive to density variation inside the Earth, and hence can be used to study lithospheric structures. Modern satellite technology provides a global coverage of gravity measurements, which makes gravity an efficient tool to probe the Earth. Inversion is a numerical technique to estimate physical properties in the subsurface from observed data. The computational burden for inversion usually increases dramatically with the size of a study region. In addition, inversion results suffer from strong ambiguity because of limited distribution of observation points and inevitable errors. We present a gravity inversion method to obtain density distributions in the lithosphere. The study region is first divided into small cells. The number of cells is adaptively adjusted in different areas to reduce the computational cost. Furthermore, the inversion method can exploit existing models of other physical properties to improve the result. This method is tested on a synthetic model and applied to real gravity data over the Tibetan Plateau, where how the Indian lithosphere has underthrusted is contentious. Low‐density anomalies identified in our density model might reflect asthenospheric upwellings and tearing of the Indian mantle lithosphere. Key Points: Adaptive refinement of inversion grid is used in gravity inversion to reduce the unknownsMultiphysical properties (e.g., velocity) are incorporated as constraints to improve the resolution of inversion resultsInversion of gravity data over the Tibetan Plateau indicates possible asthenosphere upwellings and a fragmented Indian lithosphere [ABSTRACT FROM AUTHOR]

Transient electromagnetic method (TEM) is often used in urban underground space exploration and field geological resource detection. Inversion is the most important step in data interpretation. Because of the volume effect of the TEM, the inversion results are usually multi-solvable. To reduce the multi-solvability of inversion, the constrained inversion of TEM has been studied using the least squares method. The inversion trials were performed using two three-layer theoretical geological models and one four-layer theoretical geological model. The results show that one-dimensional least squares constrained inversion is faster and more effective than unconstrained inversion. The induced electromotive force attenuation curves of the inversion model indicate that the same attenuation curve may be used for different geological conditions. Therefore, constrained inversion using known geological information can more accurately reflect the underground geological information.

In order to solve the problem of insufficient precision and ability of conventional exploration technology on the boundary of room pillar goaf, specific mining parameters, roof and surrounding rock stability and other factors, in this paper, the formation and occurrence characteristics of room and pillar goaf in Shenfu Mining Area are investigated in detail, and then the distribution range of room and pillar goaf is delineated by using ground geophysical fine imaging technology, and the target area is provided by the first borehole to guide drilling to quickly expose the goaf. Through high-precision hole peeping and 3D laser scanning technology, the accurate exploration of room pillar goaf in coal mine can be realized by continuous tracking. The advantage of this method is that it integrates the respective advantages of ground and borehole exploration technology through the surface geophysical fine imaging technology to guide drilling to quickly expose the room and pillar goaf, and the high-precision borehole scanning technology is used to realize the high-precision exploration of the room and pillar goaf boundary, specific mining parameters, roof and surrounding rock stability, and water accumulation conditions. At the same time, the drilling layout basis is sufficient, there is no invalid workload, saving the drilling quantity and drilling cost.

The galvanic distortion caused by small-scale electrical inhomogeneities near the shallow surface perturbs the overall frequency response curve of magnetotelluric (MT) records and adversely affects the imaging of deep electrical structures. Various efforts have been made to suppress the galvanic distortion, but they are still difficult to use in complex regional structures. To effectively recover the deeper electrical structures, we develop an inversion technique in which the shallow electrical structures are constrained by other types of electromagnetic data and used as part of the prior model to remove the galvanic distortion. When other types of electromagnetic data are unavailable, we can also simulate the galvanic distortion by using a refined forward mesh and putting small-scale electrical resistivity anomalies beneath the surface. We validate our inversion approach using synthetic examples and apply it to field MT data collected from the northern Trans North China Orogen. A three-dimensional electrical resistivity model is obtained based on the prior model designed according to the locations of distorted MT stations. In our resulting model, artifacts caused by galvanic distortion are removed as compared to previous work. We demonstrate that our method is effective in improving the reliability of MT inversions in complex regions, leading to better interpretations of deep electrical structures. [ABSTRACT FROM AUTHOR]

Leaf biochemical traits indicating early symptoms of plant stress can be assessed using imaging spectroscopy combined with radiative transfer modelling (RTM). In this study, we assessed the potential applicability of the leaf radiative transfer model Fluspect-Cx to simulate optical properties and estimate leaf biochemical traits through inversion of two native Australian eucalypt species: Eucalyptus dalrympleana and E. delegetensis. The comparison of measured and simulated optical properties revealed the necessity to recalibrate the refractive index and specific absorption coefficients of the eucalypt leaves’ biochemical constituents. Subsequent validation of the modified Fluspect-Cx showed a closer agreement with the spectral measurements. The average root mean square error (RMSE) of reflectance, transmittance and absorptance values within the wavelength interval of 450–1600 nm was smaller than 1%. We compared the performance of both the original and recalibrated Fluspect-Cx versions through inversions aiming to simultaneously retrieve all model inputs from leaf optical properties with and without prior information. The inversion of recalibrated Fluspect-Cx constrained by laboratory-based measurements produced a superior accuracy in estimations of leaf water content (RMSE = 0.0013 cm, NRMSE = 6.55%) and dry matter content (RMSE = 0.0036 g·cm−2, NRMSE = 21.28%). The estimation accuracies of chlorophyll content (RMSE = 8.46 µg·cm−2, NRMSE = 24.73%), carotenoid content (RMSE = 3.83 µg·cm−2, NRMSE = 30.82%) and anthocyanin content (RMSE = 1.69 µg·cm−2, NRMSE = 37.12%) were only marginally better than for the inversion without any constraints. Additionally, we investigated the possibility to substitute the prior information derived in the laboratory by non-destructive reflectance-based spectral indices sensitive to the retrieved biochemical traits, resulting in the most accurate estimation of carotenoid content (RMSE = 3.65 µg·cm−2, NRMSE = 29%). Future coupling of the recalibrated Fluspect with a forest canopy RTM is expected to facilitate retrieval of biophysical traits from spectral air/space-borne image data, allowing for assessing the actual physiological status and health of eucalypt forest canopies.

Geophysical data processing further constrained inversion is evolving progressively prevalent in geoscience domains for three-dimensional modelling and resources evaluation. The process is based on the magnetic and gravity data processing further constrained Cartesian cut cell inversion to discern the maximum of information about HAJJAR deposit in order to calculate its tonnage. This article exhibits data and inversion processing technique for tonnage calculation based on an important geophysical magnetic and gravity surveys of defined extent of HAJJAR region, which presents a great benefit to save time and have accurate and realistic results to a same case. Otherwise, the potential-field signatures of what are regarded to be geologically expressive features are sought within the magnetic and gravity data. The preliminary stage for tonnage calculation was residual anomaly processing and depth estimation of the orebody using spectral analysis method. However, progressing towards extracting the deposit signature, the used method leads to invest the gravity signature of the orebody in adequacy with the magnetic signature. Finally, the tonnage calculation was developed by constrained Cartesian cut cell inversion using Voxi Earth ModellingTM. Obtained results were very important, given their qualitative and quantitative accuracy, which give an added value for the governmental geological and geophysical survey. [ABSTRACT FROM AUTHOR]

This study uses ground penetrating radar (GPR) data as constraints in the inversion of radio-magnetotelluric (RMT) data, to provide an improved model at shallow depth. We show that modification of the model regularization matrix using all GPR common-offset (CO) reflections can mislead the constrained inversion of RMT data. To avoid such problems, common mid-point (CMP) GPR data are translated to a resistivity model by introducing a new petrophysical relationship based on a combination of Topp's and Archie's equations. This model is updated through a semi-iterative method and is employed as an initial and prior model in the subsequent inversion of RMT data. Finally, a water content model that fits the GPR CMP and RMT data is derived from the resistivity model computed by the constrained inversion of RMT data. To assess the proposed scheme, it is applied to a synthetic data set. Then, real RMT data collected along an 870 m-long profile across a known aquifer situated in the north of Heby, central Sweden, are inverted. By removing the smoothness constraints across GPR CO interfaces or using CMP-based inversion, thick (> 10 m) vadose and saturated zones are resolved and shown to correlate with logs from nearby boreholes. Nevertheless, the application of our CMP-based inversion was the only efficient scheme to retrieve thin (~ 3 m) saturated zones and the water table at a depth of 7–15 m in the RMT models. The estimated models of water content are in good agreement with the available hydrogeological information in the study area. [ABSTRACT FROM AUTHOR]

Advanced geological predictions and ascertainment of the water-bearing geological structures in front of the tunnel face are effective ways to ensure the safety of tunnel construction. Comprehensive geological predictions are often used to obtain adverse geological conditions in front of the tunnel face, and the comprehensive comparison analysis on various prediction methods can help to reduce multiplicity of solutions and improve reliability. However, in the conventional comprehensive prediction system, the prediction data for each method is separately inverted and processed, so the problem of multiple solutions in detection results for each category actually cannot be solved. Therefore a new comprehensive geological prediction method is proposed in this paper based on constrained inversion and integrated interpretation for water-bearing tunnel structures to solve the problem. Firstly, four preferred prediction methods are selected to meet the needs of the advanced detection of water-bearing structure. They are seismic reflection method, transient electromagnetic method, 3D resistivity method and ground penetrating radar (GPR) method. Then, a constrained inversion method of 3D resistivity is proposed based on the inequality and spatial structural constraints. Inequality constraint characterises the electrical resistivity variation range of the detection area, and its prior information is mainly from the geological inference and core-drilling analysis. Spatial structural constraint characterises the geological structure boundary and shape, its prior information is mainly derived from some more effective methods for geological tectonic boundary recognition such as seismic reflection and GPR methods, and it also can be derived from the disclosure by drilling exploration. The role of resistivity constrained inversion to reduce the multiple solutions of prediction is mainly reflected in data processing, and the role of integrated interpretation to reduce the multiple solutions of prediction is mainly reflected in the result interpretation process. Meanwhile, the responding characteristics of methods of seismic reflection, electromagnetism, 3D resistivity, GPR and others to the water-bearing geological structure are summarised from the differences of elasticity, electrical conductivity and dielectric constant. Therefore, an integrated interpretation guideline for water-bearing structures is proposed. Finally, a new comprehensive geological prediction technology system is established through combining the constrained inversion and the integrated interpretation. Numerical examples and engineering applications show that this method can take full advantage of the prior information of inequality constraints and spatial structures, and together with the integrated interpretation on the comprehensive geological prediction results, it has a significant effect in eliminating the false anomalies of inversion, reducing the multiple solutions of inversion and improving prediction accuracy. [ABSTRACT FROM PUBLISHER]

Full-waveform inversion for borehole seismic data is an ill-posed problem and constraining the problem is crucial. Constraints can be imposed on the data and model space through covariance matrices. Usually, they are set to a diagonal matrix. For the data space, signal polarization information can be used to evaluate the data uncertainties. The inversion forces the synthetic data to fit the polarization of observed data. A synthetic inversion for a 2D-2C data estimating a 1D elastic model shows a clear improvement, especially at the level of the receivers. For the model space, horizontal and vertical spatial correlations using a Laplace distribution can be used to fill the model space covariance matrix. This approach reduces the degree of freedom of the inverse problem, which can be quantitatively evaluated. Strong horizontal spatial correlation distances favor a tabular geological model whenever it does not contradict the data. The relaxation of the spatial correlation distances from large to small during the iterative inversion process allows the recovery of geological objects of the same size, which regularizes the inverse problem. Synthetic constrained and unconstrained inversions for 2D-2C crosswell data show the clear improvement of the inversion results when constraints are used.

ABSTRACT Geologically constrained inversion of gravity and magnetic field data of the Victoria property (located in Sudbury, Canada) was undertaken in order to update the present three-dimensional geological model. The initial and reference model was constructed based on geological information from over 950 drillholes to constrain the inversion. In addition, downhole density and magnetic susceptibility measured in six holes were statistically analysed to derive lower and upper bounds on the physical properties attributed to the lithological units in the reference model. Constrained inversion of the ground gravity and the airborne magnetic data collected at the Victoria property were performed using GRAV3D and MAG3D, respectively. A neural network was trained to predict lithological units from the physical properties measured in six holes. Then, the trained network was applied on the three-dimensional distribution of physical properties derived from the inversion models to produce a three-dimensional litho-prediction model. Some of the features evident in the lithological model are remnants of the constraints, where the data did not demand a significant change in the model from the initial constraining model (e.g., the thin pair of diabase dykes). However, some important changes away from the initial model are evident; for example, a larger body was predicted for quartz diorite, which may be related to the prospective offset dykes; a new zone was predicted as sulfide, which may represent potential mineralisation; and a geophysical subcategory of metabasalt was identified with high magnetic susceptibility and high density. The litho-prediction model agrees with the geological expectation for the three-dimensional structure at Victoria and is consistent with the geophysical data, which results in a more holistic understanding of the subsurface lithology. [ABSTRACT FROM AUTHOR]

The South Mid-Atlantic Ridge (SMAR), the most typical slow-spreading ridge on the earth, is a significant area to study the oceanic crust-mantle evolution. We used gravity data and the S-wave velocity model to derive a 3D density model of the upper-mantle beneath the South Atlantic Ocean to better understand the relationship between ridges, hotspots, and large igneous provinces. The density variations in the upper-mantle are related to thermal and compositional changes. The segment near the Agulhas-Falkland Fracture Zone (AFFZ) is characterized by low-density but inconspicuous low-velocity anomalies reflecting the depleted composition. Its composition is different from the northern part of the SMAR. A low-density layer at 100 km that extends 200 km from the ridge to the Discovery hotspot and that disappears near the AFFZ, is also present. The higher degree of mantle melting beneath the segment near the AFFZ is most probably influenced by the residual plume materials from the Discovery hotspot. Deep low densities beneath the Rio Grande Rise (RGR) and the Walvis Ridge (WR) indicate a higher degree of melting and their formation is probably influenced by the Tristan da Cunha plume. When the RGR is driven away from the plume, its original hot materials cool down and present as cold and dense uppermost mantle deposits. As the plume is located in the African plate, the WR was continuously formed as a seamount chain by intraplate volcanism of mantle plume. • Different factors dominate northern and southern segments of SMAR, respectively. • The SMAR is affected by the residual plume materials from the Discovery hotspot. • The RGR and WR were formed by the Tristan da Cunha plume. [ABSTRACT FROM AUTHOR]

The coal-bearing strata of the deep Upper Paleozoic in the GS Sag have high hydrocarbon potential. Because of the absence of seismic data, we use electromagnetic (MT) and gravity data jointly to delineate the distribution of deep targets based on well logging and geological data. First, a preliminary geological model is established by using three-dimensional (3D) MT inversion results. Second, using the formation density and gravity anomalies, the preliminary geological model is modified by interactive inversion of the gravity data. Then, we conduct MT-constrained inversion based on the modified model to obtain an optimal geological model until the deviations at all stations are minimized. Finally, the geological model and a seismic profile in the middle of the sag is analysed. We determine that the deep reflections of the seismic profile correspond to the Upper Paleozoic that reaches thickness up to 800 m. The processing of field data suggests that the joint MT-gravity modeling and constrained inversion can reduce the multiple solutions for single geophysical data and thus improve the recognition of deep formations. The MT-constrained inversion is consistent with the geological features in the seismic section. This suggests that the joint MT and gravity modeling and constrained inversion can be used to delineate deep targets in similar basins. [ABSTRACT FROM AUTHOR]

• Smoothness constraint in regularized resistivity inversion is removed at structural boundaries. • Structural unit-specific petrophysical models are used for moisture interpretation. • Moisture content is better estimated from resistivity with the new method. In Earth sciences, the measurement of soil and rock moisture content is essential in improving our understanding of various hydrologic processes. Recently, the electrical resistivity method has been frequently used to estimate the moisture content in the field. The uncertainty associated with resistivity-estimated moisture content is mainly from two sources: regularized inversion and petrophysical interpretation. In this study, to reduce the uncertainty, we propose (1) to use subsurface structural information from seismic refraction measurements to relax the smoothness-based regularization at structural boundaries and (2) to use structural unit-specific petrophysical relationships to translate resistivity into moisture content. The proposed methods are tested on a synthetic subsurface model featuring three distinct layers of a granitic critical zone (CZ). The results of the synthetic example show that both the spatial pattern and the moisture content values estimated with the new method are very close to the true model with low uncertainty. Compared to the traditional method, the estimation is significantly improved, particularly at the CZ boundaries, such as the regolith-fractured bedrock interface. We also apply the new method to a granitic hillslope to estimate the moisture content distribution from field resistivity measurements. Although no ground truth is available for validation, the estimated moisture content distributions exhibit some typical hydrological features in hillslopes, such as the perched water at the soil/rock interface and preferential flow path in fractured rocks. Therefore, it is concluded that incorporating structural information in resistivity inversion and using structural unit-specific petrophysical models can improve moisture content estimation from field resistivity measurements. [ABSTRACT FROM AUTHOR]

Abstract: Geotechnical projects usually rely on traditional sounding and drilling investigations. Drilling only provides point information and the geology needs to be interpolated between these points. Near surface geophysical methods can provide information to fill those gaps. Norwegian case studies are presented to illustrate how two-dimensional electrical resistivity tomography (ERT) can be used to accurately map the extent of quick clay deposits. Quick clay may be described as highly sensitive marine clay that changes from a relatively stiff condition to a liquid mass when disturbed. Quick clay slides present a geo-hazard and therefore layers of sensitive clay need to be mapped in detail. They are usually characterized by higher resistivity than non-sensitive clay and ERT is therefore a suitable approach to identify their occurrence. However, our experience shows that ERT cannot resolve this small resistivity contrast near large anomalies such as a bedrock interface. For this reason, a constrained inversion of ERT data was applied to delineate quick clay extent both vertically and laterally. As compared to the conventional unconstrained inversions, the constrained inversion models exhibit sharper resistivity contrasts and their resistivity values agree better with in situ measurements. [Copyright &y& Elsevier]

Abstract: Magnetotelluric surveys were conducted to investigate the structure in the El Hito Anticline in the southern Loranca Basin, Spain. The structure of this anticline is partly known from nearby data (geological cross sections, geological maps, well-logs) from vintage geophysical and geological basin-scale surveys. Unfortunately, these surveys do not have the appropriate resolution to determine certain characteristics of the anticline accurately, such as the thickness or geometry of geological units. To address this deficiency, magnetotelluric data were acquired at 51 sites along three profiles to image the electrical resistivity of the anticline. To identify a geologically reasonable resistivity model, a conceptual model based on previous geological and geophysical information (cross sections and well-log data) was generated. Several inversions were performed using the conceptual model, which played a key role in the interpretation of the magnetotelluric data, and the construction of a suitable initial model was essential in producing geologically meaningful models. Using these results, we obtained 2-D resistivity models that provide information on the main geological units and structures. We also performed sensitivity tests to understand the morphology and structure of the resistive basement better. The results indicate the presence of basement highs that show different structural styles for the basement and its cover, and an increase in the basement depth towards the south. The final 2-D resistivity models provide new information regarding the structure of the anticline and demonstrate a clear correlation between the main geological units and resistivity, as well as correlations with mapped surface faults. [Copyright &y& Elsevier]

ABSTRACT We present a joint inversion scheme that couples P-wave refraction and seismic surface-wave data for a layered subsurface. An algorithm is implemented with a damped least-squares approach. The estimated parameters are S- and P-wave velocities and layer thicknesses, while densities are assumed constant during inversion. The coupling is both geometric and physical: layer thicknesses are the same for S- and P-wave velocity profiles and P-wave velocities enter in both forward algorithms. Sensitivity analysis, performed on synthetic data, reveals that surface-wave dispersion curves can be sensitive also to P-wave velocity of some layers (especially for Poisson's ratio values smaller than about 0.35), allowing synergic resolution of this parameter. Applications on both synthetic and field data show that the proposed approach mitigates the hidden layer problem of seismic refraction and leads to more accurate results than individual inversions also for surface waves. Additional constraints on the objective function on a priori Poisson's ratio values allow unrealistic and not admissible VP and VS values to be avoided; such constraints were applied in one field case considering the a priori information available about water-table depth. It is also shown that estimation of porosity can help the selection of the proper constraint on a priori Poisson's ratio. [ABSTRACT FROM AUTHOR]

Abstract: Quality factors (Q) of near-surface materials are as important as velocities of the materials in many applications. Only phase information of surface-wave data is utilized when high-frequency (≥2Hz) surface-wave data are routinely inverted to determine near-surface shear (S)-wave velocities. Amplitude information of high-frequency surface-wave data can be used to determine quality factors of near-surface materials. Given S-wave velocity, compressional (P)-wave velocity, and Rayleigh-wave phase velocities, it is feasible to solve for S-wave quality factor QS and P-wave quality factor QP (for some specific velocity models) down to 30m below the ground surface in many settings by inverting high-frequency Rayleigh-wave attenuation coefficients in a layered earth model. Amplitude of seismic data is an exponential function of attenuation coefficients. When calculating attenuation coefficients from changes in amplitude, this nonlinear nature would result in that small variations in amplitude cause huge changes in attenuation coefficients. This result suggests data (attenuation coefficients) that normally possess large errors could eventually transfer to a model (quality factors); therefore, constraints (or a priori information) on models are necessary. Because an inversion system to solve this problem is unstable, a regularization parameter must be introduced into an inversion algorithm to stabilize the inversion. These characteristics of the inversion problem allow us to solve the problem as a constrained and regularized linear system. Usually, a set of models that meet the defined constraints can be obtained by solving the system. Based on the linear nature of the inversion system, a smooth model can be selected from the set of models as a solution of the inversion using the L-curve method. This approach is a trade-off solution between data misfit and model length. Several real-world examples demonstrate the importance of constraints in finding acceptable realistic quality factors from empirical data. [Copyright &y& Elsevier]

Abstract: Surface-based ground penetrating radar (GPR) and electrical resistance tomography (ERT) are common tools for aquifer characterization, because both methods provide data that are sensitive to hydrogeologically relevant quantities. To retrieve bulk subsurface properties at high resolution, we suggest incorporating structural information derived from GPR reflection data when inverting surface ERT data. This reduces resolution limitations, which might hinder quantitative interpretations. Surface-based GPR reflection and ERT data have been recorded on an exposed gravel bar within a restored section of a previously channelized river in northeastern Switzerland to characterize an underlying gravel aquifer. The GPR reflection data acquired over an area of 240×40m map the aquifer''s thickness and two internal sub-horizontal regions with different depositional patterns. The interface between these two regions and the boundary of the aquifer with the underlying clay are incorporated in an unstructured ERT mesh. Subsequent inversions are performed without applying smoothness constraints across these boundaries. Inversion models obtained by using these structural constraints contain subtle resistivity variations within the aquifer that are hardly visible in standard inversion models as a result of strong vertical smearing in the latter. In the upper aquifer region, with high GPR coherency and horizontal layering, the resistivity is moderately high (>300Ωm). We suggest that this region consists of sediments that were rearranged during more than a century of channelized flow. In the lower low coherency region, the GPR image reveals fluvial features (e.g., foresets) and generally more heterogeneous deposits. In this region, the resistivity is lower (~200Ωm), which we attribute to increased amounts of fines in some of the well-sorted fluvial deposits. We also find elongated conductive anomalies that correspond to the location of river embankments that were removed in 2002. [Copyright &y& Elsevier]

Abstract: Two inversions, unconstrained and constrained, of a gravity survey of the Matagami mining camp (Abitibi Archaean Subprovince, Canada) have been performed in order to identify the downward extension of a rhyolitic horizon hosting VMS-type base metals deposit and the morphologies of the major felsic plutons. A comparative study exhibits the similarities between measured and calculated densities from chemical compositions of the Matagami lithologies. This allows building an initial 3D geodensity model which integrates densities and available structural and geological surface mapping data. This model is integrated during the iteration process of the constrained inversion in the objective function. The resulting true density model and two derived cross-sections upgrade the 3D imaging of this area. Also, the model gives new insight for regional geological interpretation exposing possible shapes of the main geological units at depth and suggests the potential existence of deep fertile geological bodies. [Copyright &y& Elsevier]

Leaf biochemical traits indicating early symptoms of plant stress can be assessed using imaging spectroscopy combined with radiative transfer modelling (RTM). In this study, we assessed the potential applicability of the leaf radiative transfer model Fluspect-Cx to simulate optical properties and estimate leaf biochemical traits through inversion of two native Australian eucalypt species: Eucalyptus dalrympleana and E. delegetensis. The comparison of measured and simulated optical properties revealed the necessity to recalibrate the refractive index and specific absorption coefficients of the eucalypt leaves' biochemical constituents. Subsequent validation of the modified Fluspect-Cx showed a closer agreement with the spectral measurements. The average root mean square error (RMSE) of reflectance, transmittance and absorptance values within the wavelength interval of 450–1600 nm was smaller than 1%. We compared the performance of both the original and recalibrated Fluspect-Cx versions through inversions aiming to simultaneously retrieve all model inputs from leaf optical properties with and without prior information. The inversion of recalibrated Fluspect-Cx constrained by laboratory-based measurements produced a superior accuracy in estimations of leaf water content (RMSE = 0.0013 cm, NRMSE = 6.55%) and dry matter content (RMSE = 0.0036 g·cm−2, NRMSE = 21.28%). The estimation accuracies of chlorophyll content (RMSE = 8.46 µg·cm−2, NRMSE = 24.73%), carotenoid content (RMSE = 3.83 µg·cm−2, NRMSE = 30.82%) and anthocyanin content (RMSE = 1.69 µg·cm−2, NRMSE = 37.12%) were only marginally better than for the inversion without any constraints. Additionally, we investigated the possibility to substitute the prior information derived in the laboratory by non-destructive reflectance-based spectral indices sensitive to the retrieved biochemical traits, resulting in the most accurate estimation of carotenoid content (RMSE = 3.65 µg·cm−2, NRMSE = 29%). Future coupling of the recalibrated Fluspect with a forest canopy RTM is expected to facilitate retrieval of biophysical traits from spectral air/space-borne image data, allowing for assessing the actual physiological status and health of eucalypt forest canopies. [ABSTRACT FROM AUTHOR]

What are the anomalous seismic reflection bodies at depths of over 6000 m? Are they reefs or igneous rock? This is a difficult problem for seismic techniques, but the GMES technique can handle it. The GMES technique is a joint exploration technique combining gravity, magnetic, electrical, and seismic techniques. The specific procedure is to conduct a 2D interface-constrained CEMP inversion using 2D seismic and log data followed by a property parameter inversion of the anomalous bodies using gravity and seismic data by the stripping technique. We then estimate the physical properties of the anomalous bodies, such as density, susceptibility, resistivity, velocity, and etc. to deduce the geological features of the bodies and provide a basis for drilling decisions. The work in the TZ area reported in this paper shows the applicability of the technique. [ABSTRACT FROM AUTHOR]

A detailed magnetotelluric survey was carried out in the northern part of Subandean fold belt, Bolivia, with the main goal of better understanding of the geological structure of the sedimentary basin and petroleum system in the study area. An improvement of magnetotelluric technology was developed aimed at better imaging of resistivity structures in fold belt. A new static shift correction procedure and a new multistage unconstrained and constrained 2D inversion workflow was suggested and successfully implemented. In addition, the original 3D inversion approach was developed and its efficiency for fold belt geological settings was shown. Advances in magnetotelluric technology made it possible to obtain new geological information about the structure of the sedimentary cover in the study area. Two resistivity structural levels differing in resistivity were outlined. The boundary between levels corresponds to the top of the Carboniferous-Devonian formations, which is one the principle detachments in the northern part of Subandean fold belt. The topography of the top of the lower structural level does not correlate with structures in the upper structural level and with structures outlined by surface geology in most of the survey area. A large numbers of fault zones are outlined in the upper structural level, narrow anticlines are characterized by complicated structure (palm-tree structures). Magnetotellurics gives the most reliable position of the buried axes of anticlinal disharmonic folds, which opens up the possibility of constructing more reliable geological models using joint inversion of magnetotelluric data together with other geophysical data, first of all seismic data. Application of magnetotellurics in fold basins as complimentary to 2D seismic geophysical technology gives possibility to increase reliability of geological interpretation. • Large amount of broadband MT data was collected in Subandean fold belt. • A new static shift correction procedure was applied. • A multistage unconstrained and constrained 2D MT data inversion workflow is being discussed. • Advances in MT technology made it possible to get new geological information. • Application of magnetotellurics increases reliability of interpretation of geophysical data. [ABSTRACT FROM AUTHOR]

Full-waveform inversion for borehole seismic data is an ill-posed problem and constraining the problem is crucial. Constraints can be imposed on the data and model space through covariance matrices. Usually, they are set to a diagonal matrix. For the data space, signal polarization information can be used to evaluate the data uncertainties. The inversion forces the synthetic data to fit the polarization of observed data. A synthetic inversion for a 2D-2C data estimating a 1D elastic model shows a clear improvement, especially at the level of the receivers. For the model space, horizontal and vertical spatial correlations using a Laplace distribution can be used to fill the model space covariance matrix. This approach reduces the degree of freedom of the inverse problem, which can be quantitatively evaluated. Strong horizontal spatial correlation distances favor a tabular geological model whenever it does not contradict the data. The relaxation of the spatial correlation distances from large to small during the iterative inversion process allows the recovery of geological objects of the same size, which regularizes the inverse problem. Synthetic constrained and unconstrained inversions for 2D-2C crosswell data show the clear improvement of the inversion results when constraints are used. [ABSTRACT FROM AUTHOR]