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The Southwestern area of Fujian Province in China contains a major metallogenic belt. There have been three major tectonic movements since the Late Paleozoic, and the thrusts here are the main mineral deposits. These occurred between the Early Carboniferous and Late Permian eras. Due to dramatic undulations in the surface and associated complex underground structures, a single geophysical method cannot provide reliable imaging results. This is largely due to difficulties in data acquisition and processing. Seismic exploration provides one example. Using this method, raw shot gathers have a low signal-to-noise ratio because of the undulations in the topography. Furthermore, strong lateral velocity variation makes the migration process exceedingly difficult. This means that interpretations of the resulting reflection seismic profile give rise to uncertainty. For this reason, two-dimensional reflection seismology and controlled source audio-frequency magnetotellurics (CSAMT) electromagnetic sounding techniques were performed. After initially completing conventional processing on the seismic reflection data, subsequent pre-stack depth migration (PSDM) over the rugged topography yielded a much better image. It was able to identify thrust faults and magma intrusions. Then, using CSAMT, inversion was conducted with the same topography as the seismic reflection. By combining the migrated seismic profile, inverted resistivity profile, and borehole data, a vertical geological model was constructed. This proved the existence of an overlapped thrust, and it also indicated the possible presence of deeper mineralization. [ABSTRACT FROM AUTHOR]

Magnetotelluric (MT) and wide‐angle seismic reflection/refraction surveys play a fundamental role in understanding the crustal rheology and lithospheric structure of the Earth. In recent years, the integration of the two methods in order to improve the robustness of the inversion has started to gain attention. We present a new approach for joint 3‐D inversion of MT and wide‐angle seismic reflection/refraction data to accurately determine crustal structures and Moho depth. Based on H‐κ stacking of teleseismic receiver functions, we estimate an initial reference Moho. This is used as input for the subsequent MT/seismic joint inversion, where the Moho interface is updated and crustal structures are added to the model. During the joint inversion process, structural similarity is facilitated through the cross‐gradient constraint. Synthetic model tests show an improvement of the inversion results over separate inversions. In particular, the tests based on two geologically realistic models demonstrate that the crustal structure and even the trade‐off between velocity and Moho interface can be sufficiently resolved by combined MT and seismic data sets when using the estimates from analysis of receiver functions. These results show that the new method can provide useful constraints on crustal structures including their geophysical properties and discontinuities. Key Points: A new coupled algorithm is developed for 3‐D imaging of magnetotelluric and wide‐angle seismic reflection/refraction dataTwo strategies are presented to mitigate the problem of accurately determining crustal structures and Moho interface simultaneouslyThe inclusion of teleseismic receiver functions is proved to be effective in the new algorithm [ABSTRACT FROM AUTHOR]

New evidence concerning the middle and upper crustal structure of the Longmen Shan range where the May 12, 2008 M7.9 Wenchuan earthquake occurred is presented on the basis of seismic reflection surveys. The results of seismic reflection profiles clearly show a relatively complete stratigraphic sequence of the Upper Yangtze Basin since the Cambrian. Folding deformation, along with movements along numerous detachment layers, took place in the strata among the Wenchuan–Maoxian Fault (WMF), the Yingxiu–Beichuan Fault (YBF), and the Guanxian–Anxian Fault (GAF). The WMF is steep in the shallow strata, turning gentler gradually from a depth of 4 km, and more so at depths beyond 7 km. The WMF imbricates with the YBF and GAF, and they do not converge within the top 15 km of the crust. This interpretation disagrees with the viewpoint that the YBF and GAF extend with subvertical trend to a depth of 20 km with a robust relationship between the hypocenters and the subsurface faults and fold geometries. We conclude that the sub-horizontal detachment layers where most aftershocks occurred are the major causative fault, instead of the YBF. The YBF might be an earthquake-propagating fault according to our seismic reflection data and the distribution of aftershocks. The overlying rigid and rootless Pengguan complex (∼3–4 km) might aggravate the damage to the YBF. Furthermore, there exists a new high-angle, listric structures vertical coseismic fault, which is able to link the seismogenic detachment layer and the shallow YBF together and resulted in huge damage of the YBF. [ABSTRACT FROM AUTHOR]

The Luobusa chromite mine in Tibet, the largest chromite deposit discovered in China to date, is hosted in the Luobusa ophiolite in the eastern section of the Yarlung Zangbo suture zone. A combined seismic reflection and magnetotelluric survey was carried out on the mantle peridotites in which the chromitite deposits occur in order to investigate their origin and to prospect for other deposits in the area. The survey indicates that the Luobusa chromitite-bearing ultramafic block is a tectonic slice thrust onto the southern margin of the Gangdese batholith by multiple south-dipping faults. The maximum thickness of the ultramafic rock mass is 4 km, and it is underlain by the upper crust of the Indian Plate. Low-resistivity bodies in the upper crust of the Luobusa area lie at a depth of up to 5 km, and strata at a depth of 7 km cross the Yarlung Zangbo suture zone at a relatively small angle. Between depths of 20–50 km, there are a number of oval low-resistivity bodies, the lower parts of which might have been close to the Moho at a depth of approximately 65 km near the Yarlung Zangbo River. It is inferred that such low-resistivity bodies arise from partially molten bodies in the middle and lower crust and are related to deep tectonic activity and mantle material upwelling in the Yarlung Zangbo suture zone. [ABSTRACT FROM AUTHOR]