The method of bi-dimensional empirical mode decomposition (BEMD) and the combined methods of entropy weight–Technique for Order of Preference by Similarity to an Ideal Solution (TOPSIS) were used to decompose gravity–magnetic data and evaluate targets in the Luziyuan Pb–Zn–Fe polymetallic ore field and surrounding areas. Three meaningful bi-dimensional intrinsic mode function (BIMF) images were obtained by BEMD at different wavelengths, depicting different layers of geological architectures in the study area. The results are as follows. (1) The BIMF2 images depict the shallow local geological architecture and show positive gravity–magnetic anomalies of the skarn alteration and Pb–Zn–Fe mineralization distributed around concealed granites. (2) The BIMF3 images depict the medium-depth geological architecture, indicating that concealed granitic stocks, which are shallow extensions of a deeply concealed pluton, intruded along the NE-trending fault. (3) The BIMF4 images depict gravity–magnetic anomalies at greater depth, which likely reflect regional geological architectures, indicating the potential presence of a large, concealed intermediate-acid pluton in the negative anomaly zone. Three potential targets (A, B, and C) were delineated based on BEMD results of the original gravity–magnetic data. The entropy weight–TOPSIS evaluation results show that the ranking of the metallogenic potential of the delineated targets in the study area is B, A, and C, with relative proximity values of 0.4576, 0.3925, and 0.1499, respectively. The results of this study can be used to guide future exploration.
Trajectory analysis is the hotspot and research frontier of sedimentology and sequence stratigraphy. Compared with conventional analytical methods, trajectory analysis is aiming at identifying sedimentary systems and predicting sandstone reservoirs more directly. The definition of trajectory analysis has been made by Helland-Hansen as “The study of the lateral and vertical migration of geomorphological features and associated sedimentary environments, with emphasis on the paths and directions of migration”. Based on current research progress, the basic concepts and methods of trajectory analysis, types of basinward-migrating trajectories (ascending, flat and descending), quantitative parameters and the application in predicting deep-water sandstone reservoirs were introduced. Trajectory analysis mainly centers on two scales: Shoreline trajectories and shelf-edge trajectories. The formation of basin-floor fans has close relation with shelf-edge trajectories, and multiple case studies have confirmed that large-scale basin floor fan usually form under flat or descending shelf-edge trajectories. As research advances, trajectory analysis theory, which developed in continental margins, is believed to have been influenced by multiple factors. Thus, the accurate prediction of sandstone reservoirs requires the comprehensive consideration of the influence of sediment supply, accommodation spaces, past climate and so on. In addition, the problems and extensions of trajectory analysis were also introduced, including ①the along-strike lateral differential evolution; ② trajectory analysis theory in hydrological-closed sedimentary basins; ③the application of trajectory analysis in carbonate settings. As a developing theory, the terminology of trajectory analysis still needs standardization, and the coupling between shelf-edge trajectories and the development and distribution of deep-water sandstones also needs further understanding. The next research focus could be placed on interpreting the evolution of three-dimensional sedimentary systems, and the extension of shelf-edge trajectory theory to hydrologically-closed basin and carbonate sedimentary environments. The research methods of trajectory analysis should also follow the newest trends to allow researchers to better study the evolution of shelf-edge trajectories, for instance, integrating high-resolution seismic data and logging data, core samples, outcrops and high-resolution dating techniques to describe ancient sedimentary environment and geomorphology, combining satellite imaging, ground penetrating radar to portray the modern morphology of continental margins, and utilizing remote sensing to construct more precise three-dimensional models for outcrops. 相似文献
The evolution of large-scale landslides should be studied because, over long periods of time, primary remediation measures may suffer reduced efficiency or have to be adjusted many times. The 102 Landslide in southeast Tibet, which originally formed in 1991 with a volume of 5.1 million m3 and still exhibits post-failure activity, provides a distinctive case study. The landslide evolved from earthquake destruction and unloading, rainfall-triggered sliding, and debris flow to sands sliding slopes. The NE ringed scarp receded by 38.96 m during a five-year period (2003–2008). The total recession was 160 m with a total area of 2500 m2 during a 17-year period (1991–2008). Although several types of remediation measures were applied and were temporarily effective, the normal function of the Sichuan–Tibet Highway was affected by landslide reactivation from time to time. Actual effects of the engineering measures such as retaining walls, prestressed anchor cables, and drainage ditches confirm that hasty governance of this type of large-scale landslide is generally unfeasible over long time periods. Finally, an approach involving a tunnel running backward from the front face has been adopted as a permanent solution to large-scale moraine slope failures: This engineering practice has been in progress since April 2012. This paper describes the evolution of the 102 Landslide, the engineering interventions to mitigate the effects of the landslide on the Sichuan–Tibet Highway, and the choice of tunneling as a final mitigation measure. The present study concludes that approaches that allow escape from developing geo-hazards should always be the initial choice. 相似文献
This study examines the features and dynamical processes of subseasonal zonal oscillation of the western Pacific subtropical high (WPSH) during early summer, by performing a multivariate empirical orthogonal function (MVEOF) analysis on daily winds and a diagnosis on potential vorticity (PV) at 500 hPa for the period 1979–2016. The first MV-EOF mode is characterized by an anticyclonic anomaly occupying southeastern China to subtropical western North Pacific regions. It has a period of 10–25 days and represents zonal shift of the WPSH. When the WPSH stretches more westward, the South Asian high (SAH) extends more eastward. Above-normal precipitation is observed over the Yangtze–Huaihe River (YHR) basin. Suppressed convection with anomalous descending motion is located over the subtropical western North Pacific. The relative zonal movement of the SAH and the WPSH helps to establish an anomalous local vertical circulation of ascending motion with upper-level divergence over the YHR basin and descending motion with upper-level convergence over the subtropical western Pacific. The above local vertical circulation provides a dynamic condition for persistent rainfall over the YHR basin. An enhanced southwest flow over the WPSH’s western edge transports more moisture to eastern China, providing a necessary water vapor condition for the persistent rainfall over the YHR basin. A potential vorticity diagnosis reveals that anomalous diabatic heating is a main source for PV generation. The anomalous cooling over the subtropical western Pacific produces a local negative PV center at 500 hPa. The anomalous heating over the YHR basin generates a local positive PV center. The above south–north dipolar structure of PV anomaly along with the climatological southerly flow leads to northward advection of negative PV. These two processes are conducive to the WPSH’s westward extension. The vertical advection process is unfavorable to the westward extension but contributes to the eastward retreat of the WPSH. 相似文献