Nature Geoscience, Published online: 11 February 2025; doi:10.1038/s41561-024-01633-9
Rhabdophane contains high concentrations of the rare earth elements, yet Tobias Bamforth argues that it remains underappreciated as a significant host of these critical metals.
Nature Geoscience, Published online: 11 February 2025; doi:10.1038/s41561-025-01651-1
Sustained monitoring is essential for assessing volcanic hazards. Integration with igneous petrology is key to linking monitoring data to underlying magmatic processes.
The triggering mechanism of the substorm onset has been a major issue in magnetospheric research. Various models have been proposed so far. To understand the causal relationship of magnetotail processes associ...
Abstract
The geodetic community commonly challenges the composite hypotheses in the statistical testing of mathematical models. Since the composite hypotheses are not specified as opposed to their simple counterparts, they require a prior estimation of the model parameters. However, if the mathematical models are ill-conditioned, the regularized estimation is often applied for the parameters of interest. Due to the biased property, the regularized estimation does not rigorously originate in the principle of maximum likelihood (ML) estimation, which was the base for developing the theory of the generalized likelihood ratio (GLR) test. Since the regularized estimator of the parameters of interest is consequently inconsistent with the ML one, one cannot construct the GLR test, which is the uniformly most powerful invariant (UMPI) test. So far, only the bias correction approach has been suggested to solve this problem. In this contribution, an implicit representation of the regularized mathematical model is proposed. It eliminates the complete impact of regularized estimation on a mathematical model and delivers the misclosures analytically free from the influence of regularization. Thus, one can construct the GLR test, which belongs to the UMPI family, and then formulate the test statistic in terms of misclosures.
SummaryThe XSoDEx (eXperiment of Sodankylä Deep Exploration) project acquired in total 82 km of seismic reflection and refraction data to improve the understanding of the crustal composition and, consequently, the mineral systems of the Sodankylä region in Northern Finland. The Sodankylä region is part of the Central Lapland Greenstone belt, which is famous for its mineral resources. Here, we present the first subsurface images resulting from the seismic reflection and refraction data processing, and provide the first geological interpretation of the data. Our workflow comprised time domain signal processing, migration velocity model building and finally, focussing pre-stack depth migration. The results along the acquired seismic profile lines show a rich inventory of imaged reflectors throughout the upper crust, which in some parts can be correlated clearly with geological features at the surface and also show the complex structure of the lithological units of the Central Lapland Greenstone Belt in the investigation area. Moreover, the presumable top of the Archaean basement can be traced through all lines. The basement is partly bent up to the shallow subsurface. In places, the basement forms a dome-like outcrop. The derived results of the seismic data are in good accordance with earlier interpretations of adjacent seismic investigations. The XSoDEx seismic profiles connect the imaged reflective structures to these surveys, which were acquired over known mineral deposits.
SummaryWe invert 122 147 P, S, and PmP phase arrival-times from 1549 local earthquakes for both isotropic and azimuthally anisotropic lithospheric P-wave velocity structure beneath the region of the Longmenshan Fault zone, China. The use of PmP data significantly improves the spatial resolution of the middle-lower crust tomography. Our results show that widespread low-Vp anomalies exist in the middle and lower crust of the Songpan-Ganzi block and the Chuandian block, which contribute most crustal anisotropy. Moderate and strong earthquakes mainly occurred in the high-Vp and low-Vp transition zone, and obvious low-Vp anomalies appear below the seismogenic zone, indicating that the occurrence of earthquakes is affected by crustal fluids. The upper-crust anisotropy is mainly controlled by the stress field and local faults. The fast Vp directions (FVDs) on the Longmenshan fault zone are NE-SW in the lower crust and uppermost mantle, suggesting that the material flow is blocked by the Sichuan basin, so the flow moves in the NE-SW direction. The FVDs in the Longmenshan fault zone are different from SKS splitting measurements, suggesting that the crust and lithospheric mantle are decoupled there. Our anisotropy results also suggest that the thickening deformation of the upper crust and the middle-lower crustal flow jointly control the uplift and deformation of the Longmenshan mountain.
SummaryThe sensitivity of Rayleigh wave amplitude to Earth structure has applications to seismic tomography, both in cases where amplitude information is used to supplement phase velocity data to improve images of elastic parameters, and to correct amplitudes for local Earth structure in attenuation tomography. We review the theoretical basis of the ray theoretical approximation, in which the wave amplitudes are controlled by a combination of geometrical spreading and local changes in energy density due to Earth structure. We focus mainly on the latter effect, which we term the constant energy flux approximation. We investigate the ray theoretical basis for this approximation, test it against a full waveform simulation that verifies its accuracy, and show how it can be used to compute the sensitivity of amplitude to elastic moduli and density. We investigate how perturbing these parameters in a set of simple Earth models affects Rayleigh wave amplitudes, and demonstrate that a slow velocity heterogeneity can cause either increased or reduced amplitudes, depending upon the depth of the heterogeneity and the observation frequency. Consequently, amplitude sensitivity can be either positive or negative, and its magnitude can vary significantly with frequency. Although an added complication, the very different behavior of phase velocity and amplitudes to changes in Earth structure implies that the two types of data are complementary and suggest the effectiveness of using both in Rayleigh wave tomography.
Abstract
This short article highlights unsolved problems of magnetic reconnection in collisionless plasma. Advanced in-situ plasma measurements and simulations have enabled scientists to gain a novel understanding of magnetic reconnection. Nevertheless, outstanding questions remain concerning the complex dynamics and structures in the diffusion region, cross-scale and regional couplings, the onset of magnetic reconnection, and the details of particle energization. We discuss future directions for magnetic reconnection research, including new observations, new simulations, and interdisciplinary approaches.
The rapid melting and thinning of the Arctic ice has sparked serious concerns in the scientific community. In addition, sea ice thickness has also decreased, which makes ice cover more vulnerable to warming air and ocean temperatures.
Tracking and predicting sea level rise involves more than measuring the height of our oceans: Land along coastlines also inches up and down in elevation. Using California as a case study, a NASA-led team has shown how seemingly modest vertical land motion could significantly impact local sea levels in coming decades.
Scientists in Scotland have developed a new method to understand the heat and intensity of fires that burned out millions of years ago, which could unlock our understanding of wildfires during past and present periods of climate change.
Recent wildfires are larger and more intense than they've ever been in the historical record. If you've been watching the news at any point in the last decade, that's no surprise.
The surface of the Earth's inner core may be changing, as shown by a new study by USC scientists that detected structural changes near the planet's center, published in Nature Geoscience.
In 2018, the side of the Anak Krakatau volcano collapsed in a powerful eruption and produced a tsunami that killed hundreds and injured thousands on nearby Java and Sumatra in Indonesia. A new analysis of satellite data showed the mountainside was slipping for years and accelerated before the eruption—information that could have potentially offered a warning of the collapse.
Throughout the world, extreme weather is driving a growing death toll, exacting billions in damage, threatening food and water security and escalating forced migration. Yet some of the most sophisticated climate models—computer simulations of the Earth's vast, complex climate system, based upon the laws of physics—are missing crucial signals.
Beryllium-10, a rare radioactive isotope produced by cosmic rays in the atmosphere, provides valuable insights into the Earth's geological history. A research team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), in collaboration with the TUD Dresden University of Technology and the Australian National University (ANU), has discovered an unexpected accumulation of this isotope in samples taken from the Pacific seabed.
Nature Geoscience, Published online: 10 February 2025; doi:10.1038/s41561-025-01647-x
The rigid-body motion of Earth’s wandering inner core has now been reliably tracked over the past 20 years. With this knowledge, we can compare seismic recordings obtained when the inner core returns to the same position after moving for several years. More is changing than just the inner core position; the soft outermost inner core probably deforms.
Nature Geoscience, Published online: 10 February 2025; doi:10.1038/s41561-025-01642-2
Earth’s inner core has both changed its relative rotation rate and deformed in the past few decades, according to an analysis of seismic waves recorded when the inner core occupied the same relative location owing to its changing rotation rate.
SummaryGeodetic velocity models, derived from Global Navigation Satellite System (GNSS) velocity solutions, interpolate between sparse GNSS measurements to provide a more comprehensive view of horizontal and vertical intraplate deformation. These models contribute to improved assessment of seismic and volcanic hazards, assist in validating geodynamic models, and enable the integration of diverse datasets for comprehensive Earth science studies. Most interpolation techniques are not adequate to model the velocity distribution, especially for the horizontal velocities where the correlation between the components has to be included. Here, we apply a recent extension of the least-squares collocation interpolation technique to the velocity field solution of the EUREF Permanent GNSS Network Densification (EPND) project (EPND_D2150). The effect of known plate boundaries is accounted for during the interpolation to avoid smoothing across European micro-plates, thereby preserving the high velocity gradients at plate boundaries. The velocity model EuVeM2022 covers Europe and Anatolia, and has a resolution of 0.1○. The model can be applied, amongst other things, to correct models used for ground motion services, support tectonic studies, or identify local deformation along coasts for use in sea-level research.
SummaryThe leaky-mode dispersion extracted from seismograms and noise cross-correlation functions has gained lots of attention in recent years. It has been reported that leaky modes can provide constraints for subsurface structures, especially for P-wave velocities, which may compensate for the limits of traditional surface wave methods. For stable and reliable dispersion-curve inversion, the quantitative analysis of leaky-mode sensitivity is of great importance, which, however, has rarely been studied systematically. Limited by the forward modeling methods, the previous methods for calculating leaky-mode sensitivity are usually hindered by issues of mode skipping, low efficiency, etc. To this end, we propose an effective method that can calculate the leaky-mode sensitivity for various types of models based on the previously proposed forward modeling method named the semi-analytical spectral element method (SASEM). Using the intermediate results of SASEM, we derive analytical expressions for the sensitivity kernels with only matrix operations, which endows the sensitivity calculation procedure with high accuracy and reliability identical to the SASEM. In addition, we suggest a novel modal classification scheme to distinguish different kinds of leaky modes based on the sensitivity features. This scheme facilitates the stable identification of the most attractive guided-P modes from numerous normal and leaky modes, which removes obstacles in the dispersion-curve inversion using guided-P modes to constrain P-wave velocities. Several numerical tests are performed to demonstrate the high accuracy of the sensitivity calculation method and the effectiveness of the modal classification method. To assess the roles of leaky modes in the retrieval of underground structures, we perform comprehensive sensitivity analyses of leaky modes using both crust-scale and near-surface models. Besides the general conclusion that the joint inversion using normal and leaky modes can effectively retrieve P- and S-wave velocities, the feasibility of constraining models with the apparent Σ modes and the split guided-P mode dispersion curves has been demonstrated.
