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Controlled-source audio-frequency magnetotellurics (CSAMT) has developed rapidly in recent years and are widely used in the area of mineral and oil resource exploration as well as other fields. The current theory, numerical simulation, and inversion research are based on the assumption that the underground media have resistivity isotropy. However a large number of rock and mineral physical property tests show the resistivity of underground media is generally anisotropic. With the increasing application of CSAMT, the demand for probe accuracy of practical exploration to complex targets continues to increase. The question of how to evaluate the influence of anisotropic resistivity to CSAMT response is becoming important. To meet the demand for CSAMT response research of resistivity anisotropic media, this paper examines the CSAMT electric equations, derives and realizes a three-dimensional (3D) staggered-grid finite difference numerical simulation method of CSAMT resistivity axial anisotropy. Through building a two-dimensional (2D) resistivity anisotropy geoelectric model, we validate the 3D computation result by comparing it to the result of controlled-source electromagnetic method (CSEM) resistivity anisotropy 2D finite element program. Through simulating a 3D resistivity axial anisotropy geoelectric model, we compare and analyze the responses of equatorial configuration, axial configuration, two oblique sources and tensor source. The research shows that the tensor source is suitable for CSAMT to recognize the anisotropic effect of underground structure. [ABSTRACT FROM AUTHOR]

• Obtain 3-D resistivity structure of the Gudui geothermal field by audio magnetotelluric inversion. • Analyze the depth of heat source of the Gudui geothermal field by magnetotelluric inversion. • Establish the geothermal model and study genesis mechanism of the Gudui geothermal field. The Gudui geothermal field, situated in the Shannan region of Tibet, is classified as a shallow high-temperature hydrothermal field controlled by faults. Geothermal wells in this field can reach temperatures of up to 205 °C at a depth of 230 m, making it the highest recorded temperature for geothermal fields in China at that depth. However, the precise nature of the faults and subsurface structures within the Gudui geothermal field remains poorly understood. Therefore, to gain a deeper understanding of the structure and geothermal genesis mechanism of this field, a total of 361 audio magnetotelluric (AMT) stations were deployed, and the observed data was inverted to establish a large-scale three-dimensional resistivity structure of the study region. The obtained resistivity structure revealed multiple geothermal reservoirs underlying the Gudui geothermal field. Additionally, this structure also provided insights into the dip direction of faults, which serve as channels for water and heat flow. Furthermore, through the analysis of other existing magnetotelluric (MT) data and earthquake distribution, we were able to infer that the deep heat source of the Gudui geothermal field is a high-temperature partial melting body located approximately 5 km below the surface. The high-temperature partial melting body may originate from deep crustal heat flow. Finally, we conducted a brief discussion on the potential existence of other geothermal types in the Gudui region. [ABSTRACT FROM AUTHOR]

• Direct observation and measurement of dielectrophoresis of particle/cell. • Force balance system based on high-density microwell chip and optical tweezers. • Calibration of high reliability customized hologram optical tweezers system. • Contrast the influences of various factors on dielectrophoresis behaviors. • The system provides to study differentiation and diagnosis at the single-cell level. In this work, a quantitative and intuitive measurement of dielectrophoresis (DEP) behavior in a high-density dielectrophoretic microwell array chip was accomplished in assistance with the holographic optical tweezers. A one-dimensional force balance system with high reliability was achieved between the transverse optical trapping (TOT) force and the DEP force. The value of the DEP force was inferred by accurately calculating the TOT force, and the direction of the DEP force was observed with high-magnification microscopy. In order to estimate the availability and operability of the DEP force measurement system, we systematically investigated the influences of various external factors on the DEP behaviors of microspheres and live cells. All the quantitative measurement results, which agree well with the theory, showed that this system could serve as an accurate research tool for DEP behavior characterizations to optimize and improve the DEP-based manipulations of microparticles and live cells for a broad range of applications. The system also provides an approach to quantitatively obtain important parameters such as Clausius-Mossotti factors for cells in mediums, which could potentially be used to understand the dielectric properties of different types of cells for cell differentiation and diagnosis at the single-cell level. A quantitative and intuitive measurement of dielectrophoresis behavior was accomplished with assistance from the holographic optical tweezers. [Display omitted] [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]