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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]

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]

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]

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]

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]

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]

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]