Gravity Signal Research Articles

Effective action and black hole solutions in asymptotically safe quantum gravity

We derive the quantum effective action and the respective quantum equations of motion from multi-graviton correlation functions in asymptotically safe quantum gravity. The fully momentum-dependent couplings of three- and four-graviton scatterings are computed within the functional renormalization group approach and the effective action is reconstructed from these vertices. The resulting quantum equations of motion are solved numerically for quantum black hole geometries. Importantly, the black hole solutions show signatures of quantum gravity outside the classical horizon, which manifest in the behavior of the temporal and radial components of the metric. Three different types of solutions with distinct causal structures are identified and the phase structure of the solution space is investigated. Published by the American Physical Society 2024

GCMEbox: A MATLAB toolbox for extracting and analyzing common-mode errors from GNSS time series

High-precision global navigation satellite system (GNSS) time series data contain rich tectonic and non-tectonic motion information. However, such data also have common-mode errors (CME) related to spatiotemporal characteristics. CME will produce bias in accurate and reliable GNSS station positions and velocities estimations, ultimately deciphering erroneous geophysical signals. Currently, CME extraction methods can be divided into three categories: regional stack filtering, reference frame filtering, and statistical signal decomposition. The third method is widely used in geodetic data processing, including GNSS time series analysis, global time-varying gravity signal extraction, interferometric synthetic aperture radar (InSAR) time series analysis, etc. The demand for GNSS time series analysis software with interactive, visualization, and multifunctional features has also increased with the increase in GNSS stations. Therefore, we developed gCMEbox based on MATLAB. The gCMEbox’s primary functions include GNSS time series preprocessing, multiple statistical signal decomposition algorithms for extracting CME, GNSS time series analysis, visualization, velocity field construction, and generation of multiple time series post-processing products. Based on GNSS time series data, this study utilized the gCMEbox for data preprocessing, including format conversion, outlier removal, missing data recovery, etc. By applying statistical signal decomposition methods, gCMEbox successfully extracted CME. The primary objective of this study is to share this toolbox with the scientific community, providing a comprehensive tool for GNSS time series analysis and applications.

Refined Bathymetric Prediction Based on Feature Extraction of Gravity Field Signals: BATHY‐FE

AbstractThe resolution of altimetry‐derived gravity signals renders traditional bathymetry inversion methods inadequate for detecting short‐wavelength bathymetric features. This study presents a new global seafloor topography model by merging regional models constructed via a deep learning approach recently developed by the authors. Feature extraction techniques were used to refine each regional bathymetric model, resulting in sharpened features that are fuzzily revealed (or not seen) in global bathymetric models such as GEBCO_2023 and SRTM15+V2, especially in areas close to the poles. This is proof that, with regard to current gravity field products, conventional bathymetry inversion methods are weaker at generalizing to uncharted locations of the global ocean floor. At test points, the global seafloor model has mean error and error standard deviation of 1.75 ± 81.15 m. The refined seafloor topography can be used to supplement existing seafloor maps, especially in the polar regions. It is useful for studying seafloor geography, and also for studies in which seafloor ruggedness is required.

Lake gravity anomalies from ICESat-2 laser altimetry and geodetic radar altimetry

In the current most accepted global geopotential model, EGM2008, there are often data gaps in the source data used to compute the model over inland water. As a result, EGM2008 may be less reliable over lakes. Satellite altimetry has the potential to estimate gravity anomalies and update EGM2008 over lakes. Here, we evaluate the first attempt to extract gravity anomalies from ICESat-2 laser altimetry over several medium (100–1000 km2) and large (>1000 km2) lakes and compare them with conventional radar altimetry from CryoSat-2 and SARAL to investigate the performance of ICESat-2 for gravity determination over lakes. Aerial gravimetry from the GRAV-D project over the United States are utilized as the best estimate of the gravity field over the lakes. Gravity determination from altimetry is done using Fast Fourier Techniques (FFT) within a remove-restore geoid-to-gravity approach. The resulting altimetry derived gravity anomalies are then compared to the EGM2008 geoid over each lake with respect to GRAV-D. 18 lakes with area ranging from 108 km2 to 82,220 km2 across the United States were considered. Overall, gravity determination from ICESat-2 provides more reliable estimates than the other two radar altimetry missions. For all considered lakes, the performance of ICESat-2, measured in terms of standard deviation with GRAV-D, is comparable or better than the EGM2008 field over the same lake. Lake Pend Orielle is the best performing case, in which the standard deviation of the ICESat-2 derived gravity field is 2.14 mGal and the standard deviation of the EGM2008 gravity field is 2.66 mGal with respect to the GRAV-D measurements. Over Lake Tahoe, which is surrounded by mountainous terrain, ICESat-2 performs comparably to EGM2008 and captures clear gravity signal related to the lake’s bathymetry, whereas CryoSat-2 produces very unstable results. The method presented here for deriving gravity anomalies from altimetry applied to ICESat-2 laser altimetry data produces results that validate in supplement to the GRAV-D project over medium to large lakes in the United States.

A fresh look at the Gulf of St. Lawrence, Eastern Canada: Geophysical imaging of salt bodies and volcanic rocks in the upper Paleozoic Magdalen Basin

In the Gulf of St. Lawrence, the late Middle Devonian to early Permian Magdalen Basin hosts numerous salt bodies, but their number and geometry remained poorly constrained due to the poor quality of industry-seismic data. Salt originates from the Middle Mississippian (Visean) Windsor Group, which includes marine carbonates and evaporites. In this study, we use multibeam bathymetry as well as unpublished aerogravity and aeromagnetic data to better characterize the geometry of salt bodies. These datasets show a high degree of coherency and illustrate deformation on the seafloor, gravity lows and magnetic highs, all associated with salt bodies and overlying volcanic rocks. In map view, the geometry of individual salt bodies varies from nearly circular to ovoid and strongly elongated. Some salt bodies coalesce in complex-shaped salt walls elongated NNE, parallel to some of the faults that controlled the early stages of the Magdalen Basin development. Forward modeling indicates that low density salt bodies overlain by a 100–300 m thick volcanic pile may account for both gravity and magnetic signals. The ubiquity of mafic volcanic rocks indicates that the late Visean to Serpukhovian volcanic episode is more voluminous than previously thought. This episode is possibly associated with a series of dykes continuous for up to 225 km and with a period of underplating now recorded by a lower crustal layer with high seismic velocity.

Impact of salt diapir geometry and caprock composition on gravity survey results

With respect to difficulties seismic and magnetotellurics may have in accurate definition of exact salt diapir geometry, we performed various gravity simulations and calculations to investigate such exploration targets. Our motivation included the fact that not much has been done on caprock impact on the gravity signal. A very significant favorable condition is the high contrast of rock density between salt and basin sedimentary formations, especially carbonates. However, this can be more complicate if caprock formation is present. Therefore we defined approximate bulk density of typical caprock formation based on its usual composition, resulting in density values 2.45–2.70 g/cm3.We modelled by forward and inverse procedures the gravity signal Gz of salt diapirs with caprock of variable thickness to demonstrate to which extent the salt diapir negative gravity anomaly may be reduced by the impact of caprock formation. In the tested cases the gravity anomaly was reduced by more than 30% depending on respective caprock composition and thickness. Significant contribution to the delineation of salt diapirs themselves, as well as diapirs hidden under caprock, came from the application of horizontal gravity gradients Gzx. We showed the difference of Gzx spikes indicating the edges of density contacts according to the type of gravity survey – land or airborne. It was also proved by calculating the gravity effect of laboratory analogue models of salt deformation and extrusion.We demonstrated that gravity is still a valuable and relatively cheap tool for in-detail investigations of the salt structures within exploration projects.

Joint flexural-density modeling of the Taltal, Copiapó, and Iquique hotspot ridges and the surrounding oceanic plate, offshore Chile

Abstract Based on gravity and bathymetric data and using a novel two-dimensional joint flexural-density modeling approach, this work studies the physical properties of the oceanic Nazca plate around the Taltal, Copiapó, and Iquique hotspot ridges offshore northern Chile. The area is located westward of the Chilean Trench where the Taltal and Copiapó Ridges collide with the continental margin. The results show that the variability in density structure at different scales is a key factor in explaining the observed gravity signal, playing an important role in the lithospheric flexure and hence the elastic properties of the Nazca plate in this setting. The results can be interpreted as evidence of spatial and temporal heterogeneities in the plate-weakening process at the hotspots, magmatic underplating, and crustal and upper mantle fracturing and/or hydration. These processes might be relevant for the ascent of magma pathways of later (secondary) volcanism and influence the mechanical segmentation of the oceanic plate. The latter is critical in explaining the active seismogenic contact between the oceanic Nazca and overriding South America plates.

BTA2 regulates tiller angle and the shoot gravity response through controlling auxin content and distribution in rice.

Tiller angle is a key agricultural trait that establishes plant architecture, which in turn strongly affects grain yield by influencing planting density in rice. The shoot gravity response plays a crucial role in the regulation of tiller angle in rice, but the underlying molecular mechanism is largely unknown. Here, we report the identification of the BIG TILLER ANGLE2 (BTA2), which regulates tiller angle by controlling the shoot gravity response in rice. Loss-of-function mutation of BTA2 dramatically reduced auxin content and affected auxin distribution in rice shoot base, leading to impaired gravitropism and therefore a big tiller angle. BTA2 interacted with AUXIN RESPONSE FACTOR7 (ARF7) to modulate rice tiller angle through the gravity signaling pathway. The BTA2 protein was highly conserved during evolution. Sequence variation in the BTA2 promoter of indica cultivars harboring a less expressed BTA2 allele caused lower BTA2 expression in shoot base and thus wide tiller angle during rice domestication. Overexpression of BTA2 significantly increased grain yield in the elite rice cultivar Huanghuazhan under appropriate dense planting conditions. Our findings thus uncovered the BTA2-ARF7 module that regulates tiller angle by mediating the shoot gravity response. Our work offers a target for genetic manipulation of plant architecture and valuable information for crop improvement by producing the ideal plant type.

Automatic gait events detection with inertial measurement units: healthy subjects and moderate to severe impaired patients

BackgroundRecently, the use of inertial measurement units (IMUs) in quantitative gait analysis has been widely developed in clinical practice. Numerous methods have been developed for the automatic detection of gait events (GEs). While many of them have achieved high levels of efficiency in healthy subjects, detecting GEs in highly degraded gait from moderate to severely impaired patients remains a challenge. In this paper, we aim to present a method for improving GE detection from IMU recordings in such cases.MethodsWe recorded 10-meter gait IMU signals from 13 healthy subjects, 29 patients with multiple sclerosis, and 21 patients with post-stroke equino varus foot. An instrumented mat was used as the gold standard. Our method detects GEs from filtered acceleration free from gravity and gyration signals. Firstly, we use autocorrelation and pattern detection techniques to identify a reference stride pattern. Next, we apply multiparametric Dynamic Time Warping to annotate this pattern from a model stride, in order to detect all GEs in the signal.ResultsWe analyzed 16,819 GEs recorded from healthy subjects and achieved an F1-score of 100%, with a median absolute error of 8 ms (IQR [3–13] ms). In multiple sclerosis and equino varus foot cohorts, we analyzed 6067 and 8951 GEs, respectively, with F1-scores of 99.4% and 96.3%, and median absolute errors of 18 ms (IQR [8–39] ms) and 26 ms (IQR [12–50] ms).ConclusionsOur results are consistent with the state of the art for healthy subjects and demonstrate a good accuracy in GEs detection for pathological patients. Therefore, our proposed method provides an efficient way to detect GEs from IMU signals, even in degraded gaits. However, it should be evaluated in each cohort before being used to ensure its reliability.

Subsurface tidal gravity variation and gravimetric factor

SUMMARY Taking advantage of the simultaneous recording during 471 d between 2019 and 2021 by two superconducting gravimeters installed at the surface and 520 m under the surface at the Low Noise Underground Laboratory (LSBB) in Rustrel, France, we investigate whether a difference between the tidal gravity signals at the two locations can be detected. First, we model the periodical variations of the Earth’s gravity owing to the tidal influence from the Sun and Moon, at the Earth’s surface and at shallow depths. We provide analytical formulae for the Love numbers, gravimetric factor and gravity variation of simple spherical planetary models. We also numerically compute those parameters and function for a realistic spherical Earth model. We find that the fractional difference between the semi-diurnal tidal gravity variations at the surface and 520 m below is as small as 8.5 × 10$^{-5}$. We next evaluate the effect on the amplitude of the recorded gravity signal due to the calibration factors of the two superconducting gravimeters at LSBB. Finally, we compute the spectra of the difference between the gravity variations measured on and under the surface in the semi-diurnal band of the M$_2$ tidal wave. We find that the uncertainties associated to the calibration factors are larger than the theoretical or observational difference between the tidal gravity variations on the surface and at a 520-m depth.

Introduction to this special section: Subsurface uncertainty

Handling the nonuniqueness and ambiguity of geophysical inversion results is a major challenge in characterizing the subsurface. Geophysical inversion is the process of estimating the physical properties of the subsurface from the measured geophysical data, such as seismic, electromagnetic, gravity, or magnetic signals. However, there are often many different subsurface models that can fit the same data adequately well. Therefore, it is important to evaluate the uncertainty and reliability of the inverted models and integrate other sources of information, such as geologic, petrophysical, or geochemical data, to reduce uncertainty. Despite the industry's advances in recent decades, the number of subsurface outcomes that fall outside predicted ranges is disproportionate to the supposed certainty of those ranges. This leads to inefficient allocation of investment budgets, which is particularly painful due to the capital-intensive nature of the oil and gas industry.

Transcriptome analysis reveals critical genes and pathways of regulating the branching architecture of Lagerstroemia Indica in response to gravity signal

The branching architecture, as the main category of plant architecture, has a profound impact on creating natural beauty and plant production. Also, the gravitropic responses are involved in directional growth of all plants on earth. The crape myrtle as a kind of important ornamental plants is widely applied to urban landscaping. However, the regulatory mechanism controlling the branching architecture in response of gravity signal is poorly understood in crape myrtle. To identify the putative molecular mechanism, the transcriptome sequencing of crape myrtle in gravitropic growth was performed. Paraffin section analysis displayed dominant difference in the horizontal and erect branches. Also, large numbers of differentially expressed genes (DEGs) were identified between normal condition and gravitropic growth. Based on the KEGG analysis, the DEGs were mainly enriched in GA biosynthesis and signal transduction, starch and sucrose metabolism, and plant MAPK signaling pathway. This research enhanced our molecular comprehension of branching architecture in response to gravity signal while also enabling the practical application of these insights to improved crape myrtle as a significant ornamental species.

Quantum signature of gravity in optomechanical systems with conditional measurement

Quantum signature of gravity in optomechanical systems with conditional measurement

The relationship between GRACE gravity and the seismic b-value: a case study of the Northern Chile Triple Junction (25° S–40° S)

SUMMARY The northern Chile Triple Junction (CTJ) is characterized by the ongoing subduction of the Nazca plate beneath the South American plate. The geological structures within the subduction zone undergo complex changes, resulting in significant tectonic activities and intense seismicity along the western margin of South America. Based on the Gravity Recovery and Climate Experiment (GRACE) data and earthquake catalogues, this study selects the northern CTJ area (25° S–40° S, 75° W–65° W) as the research object, adopts the mathematical methods of independent component analysis (ICA) and principal component analysis (PCA) to separate the earthquake-related signals within the GRACE data, and fits the changes of seismic b-values through the frequency–magnitude relationship. The characteristics of gravity changes before and after seismic events, the seismic activity parameter b-values, and the relationship between the gravity signals and b-values are discussed. The results show that mathematical methods can effectively extract seismic-related gravity components from the GRACE data. ICA, compared to PCA, provides better results in capturing the temporal variations associated with b-value time-series, which exhibit good consistency in long-term trend changes. The average change of b-values in the study area is 0.66 ± 0.003, fluctuating over time. Generally, prior to larger seismic events, b-values tend to decrease. Along the western margin of South America, b-values are low; this aligns with the active tectonic activities between subducting plates. Additionally, a certain correlation between b-values and gravity changes is observed, but due to the influence of tectonic activities, the correspondence between b-values and gravity anomalies may not be consistent across different areas. The b-value is highly consistent with the strain rate model. Low b-values correspond to high strain rates along the western edge of South America, which is in line with the tectonic characteristics of frequent seismic activity in this area. A gradual concentration of gravity anomalies before major earthquakes is observed, accompanied by the gradual accumulation of smaller seismic events. Meanwhile, several months before the two major earthquakes, the spatial distribution of gravity appears to be similar to the coseismic signals, but the nature of its generation remains to be explored. These methods and results not only add to the applications of GRACE in seismic studies but also raise questions for further exploration.

Accuracy assessment of high and ultra high-resolution combined GGMs, and recent satellite-only GGMs – Case studies of Poland and Ethiopia

Abstract The launch of dedicated satellite gravity missions (CHAMP, GRACE, GOCE, and GRACE–FO), as well as the availability of gravity data from satellite altimetry and terrestrial/airborne gravity measurements have led to a growing number of Global Geopotential Models (GGMs) developed. Thus, the evaluation of GGMs is necessary to ensure their accuracy in recovering the Earth’s gravity field on local, regional, and global scales. The main objective of this research is to assess the accuracy of recent GGMs over Poland in Central Europe and Ethiopia in East Africa. Combined GGMs of high (degree and order (d/o) 2190) and ultra high-resolution (d/o 5540) as well as five satellite-only GGMs were evaluated using gravity data from absolute gravity measurements and airborne gravity surveys over Poland and Ethiopia, respectively. Based on this evaluation, the estimated accuracy of the high-resolution combined GGM is at the level of 2 mGal. The estimated accuracy for the ultra-high-resolution combined GGM is ~2.5 times lower. The satellite-only GGMs investigated recover the gravity signal at an accuracy level of 10 mGal and 26 mGal, for the areas of Poland and Ethiopia, respectively. When compensating for the omitted gravity signal using a high-resolution combined GGM and the topography model, an accuracy of 2 mGal can be achieved.

Parallel evolution of gravity sensing.

Omnipresent gravity affects all living organisms; it was a vital factor in the past and the current bottleneck for future space exploration. However, little is known about the evolution of gravity sensing and the comparative biology of gravity reception. Here, by tracing the parallel evolution of gravity sensing, we encounter situations when assemblies of homologous modules result in the emergence of non-homologous structures with similar systemic properties. This is a perfect example to study homoplasy at all levels of biological organization. Apart from numerous practical implementations for bioengineering and astrobiology, the diversity of gravity signaling presents unique reference paradigms to understand hierarchical homology transitions to the convergent evolution of integrative systems. Second, by comparing gravisensory systems in major superclades of basal metazoans (ctenophores, sponges, placozoans, cnidarians, and bilaterians), we illuminate parallel evolution and alternative solutions implemented by basal metazoans toward spatial orientation, focusing on gravitational sensitivity and locomotory integrative systems.

Subsurface geology detection from application of the gravity-related dimensionality constraint

Geophysics aims to locate bodies with varying density. We discovered an innovative approach for estimation of the location, in particular depth of a causative body, based on its relative horizontal dimensions, using a dimensionality indicator (I). The method divides the causative bodies into two types based on their horizontal spread: line of poles and point pole (LOP–PP) category, and line of poles and plane of poles (LOP–POP) category; such division allows for two distinct solutions. The method’s depth estimate relates to the relative variations of the causative body’s horizontal extent and leads to the solutions of the Euler Deconvolution method in specific cases. For causative bodies with limited and small depth extent, the estimated depth (z^0) corresponds to the center of mass, while for those with a large depth extent, z^0 relates to the center of top surface. Both the depth extent and the dimensionality of the causative body influence the depth estimates. As the depth extent increases, the influence of I on the estimated depth is more pronounced. Furthermore, the behavior of z^0 exhibits lower errors for larger values of I in LOP–POP solutions compared with LOP–PP solutions. We tested several specific model scenarios, including isolated and interfering sources with and without artificial noise. We also tested our approach on real lunar data containing two substantial linear structures and their surrounding impact basins and compared our results with the Euler deconvolution method. The lunar results align well with geology, supporting the effectiveness of this approach. The only assumption in this method is that we should choose between whether the gravity signal originates from a body within the LOP–PP category or the LOP–POP category. The depth estimation requires just one data point. Moreover, the method excels in accurately estimating the depth of anomalous causative bodies across a broad spectrum of dimensionality, from 2 to 3D. Furthermore, this approach is mathematically straightforward and reliable. As a result, it provides an efficient means of depth estimation for anomalous bodies, delivering insights into subsurface structures applicable in both planetary and engineering domains.

IGT/LAZY genes are differentially influenced by light and required for light-induced change to organ angle

BackgroundPlants adjust their growth orientations primarily in response to light and gravity signals. Considering that the gravity vector is fixed and the angle of light incidence is constantly changing, plants must somehow integrate these signals to establish organ orientation, commonly referred to as gravitropic set-point angle (GSA). The IGT gene family contains known regulators of GSA, including the gene clades LAZY, DEEPER ROOTING (DRO), and TILLER ANGLE CONTROL (TAC).ResultsHere, we investigated the influence of light on different aspects of GSA phenotypes in LAZY and DRO mutants, as well as the influence of known light signaling pathways on IGT gene expression. Phenotypic analysis revealed that LAZY and DRO genes are collectively required for changes in the angle of shoot branch tip and root growth in response to light. Single lazy1 mutant branch tips turn upward in the absence of light and in low light, similar to wild-type, and mimic triple and quadruple IGT mutants in constant light and high-light conditions, while triple and quadruple IGT/LAZY mutants show little to no response to changing light regimes. Further, the expression of IGT/LAZY genes is differentially influenced by daylength, circadian clock, and light signaling.ConclusionsCollectively, the data show that differential expression of LAZY and DRO genes are required to enable plants to alter organ angles in response to light-mediated signals.

Fusion of altimetry-derived model and ship-borne data in preparation of high-resolution marine gravity determination

SUMMARY Satellite altimetry provides major data sources for marine gravity recovery, and typical altimetry derived models, for example, DTU21 and SS V32.1, were usually released with 1 arcmin × 1 arcmin gridding interval. Their true resolution is much lower than the nominal ∼2 km level. By contrast, the in situ ship-borne measurements are considered to have better short-wavelength resolution. In this paper, we aim to propose a new method to fully utilize satellite altimetry data and ship-borne measurements, namely the frequency-domain fusion method, and give certain analysis of new method along with two spatial-domain fusion methods. Comprehensive analysis is focus on four aspects: gravity signals in fusion images, numerical verifications, power spectra, as well as coherence analysis. Initial evaluation indicates that, first, the frequency-domain fusion method has advantage in flexibility, since it can autonomously select dominant bands to fuse different data sets. Secondly, the new method retains medium-long wavelength signals from altimetry-derived model and effectively incorporate dominant short-wavelength signals of in-situ measurements, while the spatial-domain methods are essentially full-wavelength fusion and inevitably diminish the role of satellite altimetry. To some extent, the new method maximize the positive contribution of satellite altimetry measurements and efficiently exploit the benefits of ship-borne data. Finally, verification experiments were similarly designed in three regions with different amount and ratio of ship-borne data to thoroughly evaluate various methods. In two regions with gridded and dense along-cruise ship-borne data, the average accuracy of this frequency-domain fusion results is improved by 0.346 and 0.613 mGal, respectively. In a region with sparse ship-borne data, we still recommend using spatial-domain fusion methods since the new method is unable to align ship-borne data with model grid. It is concluded from the above analysis that the new method effectively incorporates the short-wavelength signals from ship-borne data into the altimetry-derived gravity field model, and it is significant that the new method maximizes the application of advantageous bands from different data sources.

Enhancement of quantum gravity signal in an optomechanical experiment

Enhancement of quantum gravity signal in an optomechanical experiment