地球科学最新文献

Scotland's Highlands are tectonically quiescent but have experienced high rates of isostatic uplift in response to deglaciation. To understand the effects of both deglaciation and regional uplift on landscape evolution, we measured the concentration of cosmogenic in situ ¹⁴C in river sands collected in Glen Feshie (Cairngorms). Like other terrestrial cosmogenic radionuclides, in situ ¹⁴C can be used to calculate basin-wide denudation rates over millennial timescales. ¹⁴C has a short half-life relative to other in situ cosmogenic radionuclides, giving it an advantage in post-glacial landscapes: Very little ¹⁴C will be inherited from exposure before glaciation of the landscape, meaning that concentrations will reflect sediment production and transport dominantly in the Holocene. When we calculate denudation rates based on the common assumption of basin-wide homogeneity of erosion, we find no correlation between topographic metrics such as the normalised channel steepness index and inferred denudation rates, which range between 0.175 and 1.356 mm/year. Based on field and remote sensing observations, we suggest that ¹⁴C becomes diluted downstream due to sediment supply from paraglacial terrace material, and develop a mixing model to test this hypothesis. We identify the terraces that are likely to contribute sediment to the channels through flood modelling, geomorphic mapping and remote sensing observations. Our mixing model indicates that the observed distribution of ¹⁴C concentrations can be explained if terrace escarpments have basin-averaged migration distances of 8 to 30 cm during large flood events. This interpretation is consistent with remotely sensed images of channel activity and terrace bank retreat within the catchment. Our results show that paraglacial sediment stores contribute to sediment fluxes in the late Holocene and highlight the on-going glacial legacy on landscape evolution.

Magnetic Field Line Curvature Scattering (FLCS) is one of the important loss mechanism for energetic particles, referring to the scattering phenomenon where charged particles experience changes in their pitch angles due to the curvature and non-uniformity of magnetic field. Previous methods evaluating FLCS were suitable for less stretched configurations like dipole magnetic fields, but under Ts05 model, they led to non-physical results, especially in regions where the adiabatic parameter $��\epsilon �$ exceeds 0.584. To address this, we developed a new method for evaluating FLCS, named the Loss Cone Offset method (LCOM). The method first anchors the offset of loss cone center due to Borovsky et al. (2022), https://doi.org/10.1029/2021ja030106 and works by constructing the pitch angle offset after one FLCS as a function of initial pitch angle and gyro-phase angle, and then correcting the function by parameters fitting using test-particle-tracing results. Our calculations can effectively evaluate particle scattering due to FLCS in the range of 0°–90° pitch angles and adiabatic parameter $��\epsilon �$ ranging from 0.1 to 0.96. Loss Cone Offset method has good compatibility with previous methods under dipole magnetic field or TS05 magnetic field with low adiabatic parameters. It can effectively avoid non-physical results under stretched magnetic field and high adiabatic parameters, and evaluate the FLCS influence. Comparison with theoretical calculations, empirical formulas, and test-particle results demonstrates that the LCOM serves as an easy-to-use and reliable model for predicting particle loss due to FLCS in the magnetospheric dynamics. Its application deepens understanding of FLCS mechanisms, providing robust methodological support for developing physical models.

With the advancement of dense seismic arrays, array-processing methods for ambient noise data have become highly effective in extracting high-quality broadband surface wave dispersion curves from ambient noise. Recent advancements in array data processing methods have enabled the extraction of multimode dispersion curves, offering improved constraints on deep Earth structures. However, these array-based methods often produce regionalized dispersion curves, and conventional phase velocity maps constructed by interpolating these dispersion curves typically have limited resolution, and display smooth images of phase velocities. In this study, we develop an array tomography method aimed at improving the resolution of ambient noise tomography by utilizing dispersion curves extracted through array-based data processing. To demonstrate the effectiveness of our method in enhancing tomography resolution, we construct fundamental-mode 2-D Rayleigh wave phase velocity maps by applying our approach to regionalized dispersion curves obtained from array-based methods in the western United States. By comparing our tomographic results with those from conventional array-based methods, we show that our method can produce more accurate and higher-resolution phase velocity maps. Additionally, our approach is versatile and can be applied to construct high-resolution 1-D and 2-D velocity structures using regionalized phase velocities obtained from various other array-based data processing methods.