Modeling and Interpreting CHAMP Magnetic Anomaly Field over China Continent Using Spherical Cap Harmonic Analysis

Based on the CHAMP Magsat data set, spherical cap harmonic analysis was used to model the magnetic fields over China continent. The data set used in the analysis includes the 15′×15′ gridded values of the CHAMP anomaly fields (latitude φ=25°N to 50°N and longitude λ=78°E to 135°E). The pole of the cap is located at φ=35°N and λ=110°E with half-angle of 30°. The maximum index (K max) of the model is 30 and the total number of model coefficients is 961, which corresponds to the minimum wavelength at the earth's surface about 400 km. The root mean square (RMS) deviations between the calculated and observed values are ～ 4 nT for ΔX, ～ 3 nT for ΔY and ～ 3.5 nT for ΔZ, respectively. Results show that positive anomalies are found mainly at the Tarim basin with ～6- 8 nT, the Yangtze platform and North China platform with ～4 nT, and the Songliao basin with ～4-6 nT. In contrast, negative anomaly is mainly located in the Tibet orogenic belt with the amplitude ～ (-6)-(-8) nT. Upward continuation of magnetic anomalies was used to semi-quantitatively separate the magnetic anomalies in different depths of crust. The magnetic anomalies at the earth's surface are from -6 to 10 nT for upper crust, middle crust -27 to 42 nT and lower crust -12 to 18 nT, respectively. The strikes of the magnetic anomalies for the upper crust are consistent with those for the middle crust, but not for the lower crust. The high positive magnetic anomalies mainly result from the old continental nucleus and diastrophic block (e.g. middle Sichuan continental nucleus, middle Tarim basin continental nucleus, Junggar diastrophic block and Qaidam diastrophic block). The amplitudes of the magnetic anomalies of the old continental nucleus and diastrophic block are related to evolution of deep crust. These results improve our understanding of the crustal structure over China continent.

IMAGING OF EEG BY SPHERICAL HARMONIC ANALYSIS

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Effect of morphological gene mutation and decay on energy dissipation behaviour of granular soils

In this paper,the X-ray micro-computed tomography(X-rayμCT),spherical harmonical-based principal component analysis(SH-PCA),and discrete element method(DEM)were incorporated to generate virtual samples with morphological gene mutation at different length scales.All samples were subjected to axial compression and constant confining stress.The effects of multiscale particle morphology on the stress-strain and energy storage/dissipation responses of granular soils were investigated.It is found that:(a)the effects of particle morphology on the initial stiffness,stress-strain,volumetric strain,and frictional energy dissipation behaviours are more pronounced for looser samples than for denser ones;(b)among different length scales,the particle morphology at the local roundness-level outperforms the one at the general form-level in dictating the macro-scale responses of granular soils;(c)the energy dissipation of a granular assemblage is a result of competition between particle morphology and initial void ratio.

A high resolution lithospheric magnetic field model over China

CHAMP satellite data and ground-based magnetic observations are used and combined to map the lithospheric magnetic field over China by means of the revised spherical cap harmonic analysis(R-SHCA)modeling technique.The magnetic field is described to a spatial resolution of 150 km at the mean Earth’s radius,which represents a good compromise between the resolutions afforded by surface and satellite data.We compare the magnetic anomalies modeled at the regional scale with composite regions containing large-scale of tectonic structures.These regions,including the Tarim Basin and the Tibetan Plateau,are correlated with regional magnetic anomalies at satellite altitude but contain a significant number of small-scale and complex magnetic structures at the mean Earth’s radius.These magnetic anomalies are globally consistent with the known geological features in China but also offer a way to delineate the contours of the geological blocks and to discuss the connection between magnetic anomalies and the heat flow distribution in this region.

DEM study on effect of particle roundness on biaxial shearing of sand

In this study,discrete element method(DEM)simulations of a biaxial test were used to examine the effect of particle roundness on the mechanical behavior of sands at both the macro and micro scales.First,a stack of microcomputed tomography images were binarized,segmented,and labeled using advanced image processing and analysis techniques.Second,a spherical harmonic(SH)analysis,which involves a complete set of orthogonal functions,was implemented to rebuild the natural particle shape.Then,five templates of virtual particles were built in a DEM simulation,four of which were obtained from SH degrees of 3,8,12,and 15,and one template was an elementary sphere.A flexible membrane was numerically generated to allow the material to deform freely under a prescribed confining stress.Finally,the effect of particle roundness on the mechanical properties of granular materials was investigated and discussed.Two shear bands were found to intersect,forming an X shape in both the rotation and displacement fields.Moreover,a lower particle roundness results in higher deviatoric stress and stronger dilation in the volumetric change.A decrease in particle roundness leads to less rotation of particles despite a higher displacement value.In addition,a larger SH degree leads to smaller normalized contact forces of the particles.This implies that decreasing the roundness results in higher anisotropy of the contact forces.