In this work, we interpreted gravity data to determine the structural characteristics responsible for high-gravity anomalies in Bagodo, North Cameroon. These anomalies had not previously been characterized through a local study. Thus, we undertook a regional–residual separation of the gravity anomalies by using the polynomial method. Geophysical signatures of near-surface small-extent geological structures were revealed. To conduct a quantitative interpretation of the gravity anomalies, one profile was drawn on a residual Bouguer anomaly map and then interpreted by spectral analysis, the ideal body solution, and 2.5-dimensional modeling. Our results showed that the intrusive body in the Bagodo area consists of two trapezoidal blocks. The first and second blocks have roofs approximately 7.5 and 14 km deep, respectively, whereas their bases are approximately 17 km deep. These values are in agreement with those obtained by the ideal body solution, which showed two cells with a density contrast of 0.3 g·cm−3 in comparison with the surrounding rocks. The density of this body was estimated to be approximately 3 g·cm−3. The topography of these rocks showed that they are basaltic rocks that would have cooled in fracture zones as an intrusion.
We present a statistical study of “trunk-like” structures observed in He+ and O+ in the inner magnetosphere. The main characteristic of these structures is that the energy of the peak flux decreases earthward. Using observations from the Helium Oxygen Proton Electron (HOPE) instrument onboard Van Allen Probe A, we identify the trunks observed from November 2012 to June 2019 and obtain the universal time, L shell, magnetic local time (MLT), and energy information of each trunk’s root and tip. We then investigate the behavior of trunks in terms of their frequency of occurrence, temporal evolution, spatial and energy distribution, and trunk dependence on different geomagnetic indices. We find that (1) the trunks are always located at L = 1.5−4.0 and have a preferential location mainly concentrated at MLT = 18−24, (2) the sector within MLT = 14−16 is a forbidden zone without trunk roots, and (3) the energy of He+ trunks is the largest near dusk and gradually decreases in the counterclockwise direction, whereas the energy of O+ trunks is relatively evenly distributed with MLT and L. The differences between He+ and O+ trunks are probably due to the different charge exchange and Coulomb collision lifetime. The dependence on different geomagnetic indices indicates that the trunk structures occur more frequently during relatively quiet periods.
Water is essential for the formation of a magmatic arc by lowering the melting temperature of materials in the mantle wedge. As such, it is logical to attribute the absence of a magmatic arc to insufficient water released from the subducting plate, although a number of other factors may cause volcanic arc quiescence as well, such as a slab window or flat slab subduction. In this contribution, we present a possible but testable correlation between the occurrence of a magmatic arc and seamount subduction in light of bathymetric data obtained near trenches. This correlation, if it holds true, in turn means that a magmatic arc is unlikely to occur when the subducting slabs have not been severely fractured and that one of the main reasons for excluding effects such as the slab window or flat slab subduction may be that the plate is not accompanied by seamounts. Therefore, the role that seamount subduction plays in recycling water back into the mantle deserves more attention from the earth sciences community.
During an experiment involving the alternating O / X mode pump, the Incoherent Scatter Radar (ISR) observation demonstrated that the high frequency enhanced ion line (HFIL) and plasma line (HFPL) did not immediately appear, but were delayed by a few seconds after the pump onset. By examining the initial behaviors of the ion line, plasma line and electron temperature as well as ionosphere condition, it is shown that (1) the HFIL and HFPL are delayed not only in the X mode pump but also in the O mode pump; (2) the HFIL can not be observed until the electron temperature is enhanced. The analysis suggests that (1) the leakage of the X mode to the O mode pump may not be ignored; (2) the spatiotemporal uncertainty, the spatiotemporal change in the profiles of ion mass and electron density, may play an important role in the lack of the Bragg condition; (3) nevertheless, the absence of parametric decay instability can not be ruled out due to the lack of matching condition caused by the spatiotemporal uncertainty.
It is widely believed that the electromagnetic ion cyclotron (EMIC) waves play an important role in influencing the radiation belt and ring current dynamics. Most studies investigated the effects or characteristics of EMIC waves assuming their left-handed polarization. However, recent studies found that the polarization reversal, which occurs at higher latitudes along the wave propagation path, can change the wave-induced pitch angle diffusion coefficients. Whether such a polarization reversal can influence the global ring current dynamics remains unknown. In this study, we investigate the ring current dynamics and proton precipitation loss in association with the polarization reversed EMIC waves using the Ring current - Atmosphere interactions Model (RAM). The results indicate that the polarization reversal of H-Band EMIC waves truly can decrease the scattering rates of protons of 10 to 50 keV or > 100 keV by comparing with the scenario where the EMIC waves are considered as purely left-handed polarized. Additionally, it is found that the global ring current intensity and proton precipitation can be slightly affected by the polarization reversal, especially during the prestorm and recovery phase, but the effects are not that large during the main phase. This is probably because the H-Band EMIC waves contribute to the proton scattering loss primarily at E < 10 keV, an energy range that is not strongly affected by the polarization reversal.
The plasma density is an important factor in determining wave-particle interaction in the magnetosphere. We develop a machine learning-based electron density (MLED) model in the inner magnetosphere using a data set of electron density from Van Allen Probes between September 25, 2012 and August 30, 2019. This MLED model is a physics-based nonlinear network that employs fundamental physical principles to represent the variation of electron density. It predicts the plasmapause location under different geomagnetic activities and models the electron density of the plasmasphere and trough separately. We train the model using gradient descent and backpropagation algorithms, which can be widely used to deal effectively with nonlinear relationships among physical quantities in space plasma environments. The model gives explicit expressions with few parameters and describes the association of electron density with geomagnetic activity, solar cycle, and seasonal effects. Under various geomagnetic conditions, the electron densities calculated by this model agree well with the observation and provide a good description of the plasmapause movement. This MLED model, which can be easily incorporated into the previously developed radiation belt model, would be very helpful in modeling and forecasting the radiation belt electron dynamics.
In the last decades, global seismic observations have identified increasingly complex anisotropy of the Earth’s inner core. Plenty of seismic studies have confirmed the anisotropy presents hemispherical variations in inner core. Here we report the effect of light elements on the anisotropy of hcp iron under inner core conditions based on ab initio molecular dynamics calculations. We found that light elements have significant effects on the density, sound velocities, and the anisotropy of hcp-Fe-X (X = C, O, Si, and S) binary alloy. For these binary alloys, the anisotropy depends on combined effects of temperature and the type of light element. Furthermore, there is a certain increase of the anisotropy strength with the increasing temperature. Alloying iron with some light elements such as C or O actually does not improve but reduces the strength of anisotropy of pure iron at high temperatures. Oppositely, light element S can significantly enhance the elastic anisotropy strength of hcp-Fe.
The role of Moonquake hazard distribution (peak ground acceleration, PGA; instrumental intensity Moonquakes scale, IIM) on the co-seismic moment is critical for understanding the lunar quake (including the shallow and deep lunar quakes). Here, we use Lagrangian analysis methods and lunar surface image extraction-calibration technologies to investigate the relationship between the co-seismic induced ground motion (PGA and IIM) and the rolling trajectories of the lunar boulder on the lunar slope. First, the inverse algorithm, the validation of IIM (00.18g_m), the certain critical rolling condition between the PGA and the IIM, and the falling boulder are obtained. Then, the correlation between IIM scale (scale I, ~ 0 m⁄s^2 ; scale II, ~ 0.0017g_m; scale III, 0.0017g_m0.014g_m; scale IV, 0.014 g_m0.039g_m; scale V, 0.039 g_m0.092g_m; scale VI, 0.092g_m0.18g_m) and different parameters (e.g., lunar slope 1°44°; lasting time, t, 0.12s ; fixed PGA coefficient, the ratio of the vertical component to the horizontal component of PGA amplitude, A_y0⁄A_x0 =2) is simulated and discussed. All these results play an important role in understanding lunar quakes' mechanism and the internal structure evolution. The elevation extraction-calibration technologies with the particular software for automatically recognizing lunar-terrain observational images and data (e.g., high-resolution satellite lunar imagery from NASA's lunar reconnaissance orbiter narrow-angle camera) driven IIM with observational trajectories of the lunar boulder are presented in Part II and Part III of this three-paper series studies, respectively. We anticipate our studies to be a key point, give new insights for understanding the role of PGA and IIM, and help assess the stabilities of the rovers (e.g., Zhurong rover, Chang'e series rover) in China's Moon and Mars exploration program.
The uplift of the Qinghai-Tibet Plateau (TP) strongly influences climate change, both regionally and globally. Surface observation data from this region have limited coverage and are difficult to obtain. Consequently, the vertical crustal deformation velocity (VCDV) distribution of the TP is poorly constrained. In this study, VCDV from the TP was inverted using data from the gravity recovery and climate experiment (GRACE). Based on the assumption that the gravity signal detected by GRACE is mainly composed of hydrological factors and vertical crustal movement, by deducting hydrological factors, the vertical crustal movement could be obtained. From this, the distribution of the vertical crustal deformation velocity across the TP was inverted. The results show that the VCDV of the southern, eastern, and northern TP is ~1.1 mm/a, ~0.5 mm/a, and −0.1 mm/a, respectively, while that of the region between the Qilian Haiyuan Fault and Kunlun Fault is ~0.0 mm/a. These results are consistent with the distributions of crustal deformation, thrust earthquakes/faults, and regional lithospheric activity. Hydrology, crustal thickness, and topographic factors do not change the overall distribution of the VCDV across the TP. The influence of hydrological factors is marked, with the maximum differences being approximately −0.4 mm/a in the northwest and 1.0 mm/a in the central area. The results of this study are significant for understanding the kinematics of the TP.
Water budget closure is a method used to study the balance of basin water storage and the dynamics of relevant hydrological components (e.g., precipitation, evapotranspiration, and runoff). When water budget closure is connected with terrestrial water storage change (TWSC) estimated from Gravity Recovery and Climate Experiment (GRACE) data, variations in basin runoff can be understood comprehensively. In this study, total runoff variations in the Yangtze River Basin (YRB) and its sub-basins are examined in detail based on the water budget closure equation. We compare and combine mainstream precipitation and evapotranspiration models to determine the best estimate of precipitation minus evapotranspiration. In addition, we consider human water consumption, which has been neglected in earlier studies, and discuss its impact. To evaluate the effectiveness and accuracy of the combined hydrological models in estimating subsurface runoff, we collect discharge variations derived from in situ observations in the YRB and its sub-basins and compare these data with the models’ final estimated runoff variations. The estimated runoff variations suggest that runoff over the YRB has been increasing, especially in the lower sub-basins and in the post-monsoon season, and is accompanied by apparent terrestrial water loss.
The tidal Love numbers of the Moon are a set of nondimensional parameters that describe the deformation responses of the Moon to the tidal forces of external celestial bodies. They play an important role in the theoretical calculation of the Moon’s tidal deformation and the inversion of its internal structure. In this study, we introduce the basic theory for the theoretical calculation of the tidal Love numbers and propose a new method of solving the tidal Love numbers: the spectral element method. Moreover, we explain the mathematical theory and advantages of this method. On the basis of this new method, using 10 published lunar internal structure reference models, the lunar surface and lunar internal tidal Love numbers were calculated, and the influence of different lunar models on the calculated Love numbers was analyzed. Results of the calculation showed that the difference in the second-degree lunar surface Love numbers among different lunar models was within 8.5%, the influence on the maximum vertical displacement on the lunar surface could reach ±8.5 mm, and the influence on the maximum gravity change could reach ±6 μGal. Regarding the influence on the Love numbers inside the Moon, different lunar models had a greater impact on the Love numbers h2 and l2 than on k2 in the lower lunar mantle and core.
The Neogene Terror Rift in the Antarctic Victoria Land Basin (VLB) of the Ross Sea, Antarctica, is composed of the Discovery Graben and the Lee Arch. Many Neogene volcanoes are aligned in the north-south direction in the southern VLB, belonging to the McMurdo Volcanic Group. However, due to multiple glaciations and limited seismic data, the volcanic processes are still unclear in the northern VLB, especially in the Terror Rift. Multichannel seismic profiles were collected at the VLB from the 32nd Chinese National Antarctic Research Expedition (CHINARE). We utilized four seismic profiles from the CHINARE and additional historical profiles, along with gravity and magnetic anomalies, to analyze faults and stratigraphic characteristics in the northern Terror Rift and volcanism in the VLB. Negative flower structures found in the northern Terror Rift suggest that the Terror Rift was affected by dextral strike-slip faults extending from the northern Victoria Land (NVL). After the initial orthogonal tension, the rift transited into an oblique extension, forming a set of downward concaving normal faults and accommodation zones in the Terror Rift. On the Lee Arch, several imbricated normal faults formed and converged into a detachment fault. Under gravitational forces, the strata bent upward and formed a rollover anticline. Many deep faults and thin strata subjected to erosion facilitated volcanic activity. A brittle volcanic region in the VLB was affected by dextral strike-slip movements and east-west extension, resulting in two Neogene volcanic chains that connect three igneous provinces in the VLB: the Hallett, Melbourne, and Erebus Provinces. These two chains contain mud volcanoes with magnetic nuclei, volcanic intrusions, and late-stage volcanic eruptions. Volcanisms have brought about opposite polarities of magnetic anomalies in Antarctica, indicating the occurrence of multiple volcanic activities.
Because of the viscoelasticity of the subsurface medium, seismic waves will inherently attenuate during propagation, which lowers the resolution of the acquired seismic records. Inverse-Q filtering, as a typical approach to compensating for seismic attenuation, can efficiently recover high-resolution seismic data from attenuation. Whereas most efforts are focused on compensating for high-frequency energy and improving the stability of amplitude compensation by inverse-Q filtering, low-frequency leakage may occur as the high-frequency component is boosted. In this article, we propose a compensation scheme that promotes the preservation of low-frequency energy in the seismic data. We constructed an adaptive shaping operator based on spectral-shaping regularization by tailoring the frequency spectra of the seismic data. We then performed inverse-Q filtering in an inversion scheme. This data-driven shaping operator can regularize and balance the spectral-energy distribution for the compensated records and can maintain the low-frequency ratio by constraining the overcompensation for high-frequency energy. Synthetic tests and applications on prestack common-reflection-point gathers indicated that the proposed method can preserve the relative energy of low-frequency components while fulfilling stable high-frequency compensation.
In a recent paper (Luo H et al., 2022), we found that the peak amplitudes of diurnal magnetic variations, measured during martian days (sols) at the InSight landing site, exhibited quasi Carrington-Rotation (qCR) periods at higher eigenmodes of the natural orthogonal components (NOC); these results were based on ~664 sols of magnetic field measurements. However, the source of these periodic variations is still unknown. In this paper we introduce the neutral-wind driven ionospheric dynamo current model (e.g., Lillis et al., 2019) to investigate the source. Four candidates — the draped IMF, electron density/plasma density, the neutral densities, and the electron temperature in the ionosphere with artificial qCR periodicity, are applied in the modeling to find the main factor likely to be causing the observed surface magnetic field variations that exhibit the same qCR periods. Results show that the electron density/plasma density, which controls the total conductivity in the dynamo region, appears to account for the greatest part of the surface qCR variations; its contribution reaches about 67.6%. The draped IMF, the neutral densities, and the electron temperature account, respectively, for only about 12.9%, 10.3%, and 9.2% of the variations. Our study implies that the qCR magnetic variations on the Martian surface are due primarily to variations of the dynamo currents caused by the electron density variations. We suggest also that the time-varying fields with the qCR period could be used to probe the Martian interior's electrical conductivity structure to a depth of at least 700 km.
Numerous linear grooves have long been recognized as covering the surface of Phobos, but the mechanisms of their formation are still unclear. One possible mechanism is related to the largest crater on Phobos, the Stickney crater, whose impact ejecta may slide, roll, bounce, and engrave groove-like features on Phobos. When the launch velocity is higher than the escape velocity, the impact ejecta can escape Phobos. A portion of these high-velocity ejecta are dragged by the gravitational force of Mars, fall back, and reimpact Phobos. In this research, we numerically test the hypothesis that the orbital ejecta of the Stickney crater that reimpact Phobos could be responsible for a particular subset of the observed grooves on Phobos. We adopt impact hydrocode iSALE-2D (impact-Simplified Arbitrary Lagrangian Eulerian, two-dimensional) to simulate the formation of the Stickney crater and track its impact ejecta, with a focus on orbital ejecta with launch velocities greater than the escape velocity of Phobos. The launch velocity distribution of the ejecta particles is then used to calculate their trajectories in space and determine their fates. For orbital ejecta reimpacting Phobos, we then apply the sliding boulder model to calculate the ejecta paths, which are compared with the observed groove distribution and length to search for causal relationships. Our ejecta trajectory calculations suggest that only ~1% of the orbital ejecta from the Stickney crater can reimpact Phobos. Applying the sliding boulder model, we predict ejecta sliding paths of 9−20 km in a westward direction to the east of the zone of avoidance, closely matching the observed grooves in that region. The best-fit model assumes an ejecta radius of ~150 m and a speed restitution coefficient of 0.3, consistent with the expected ejecta and regolith properties. Our calculations thus suggest the groove class located to the east of the zone of avoidance may have been caused by reimpact orbital ejecta from the Stickney crater.