Space Geodetic Data Research Articles

GREAT: A scientific software platform for satellite geodesy and multi-source fusion navigation

The software platform named GNSS + REsearch, Application and Teaching (GREAT) has been designed and developed by Wuhan University for satellite geodesy and multi-source fusion navigation. GREAT is a comprehensive software platform based on C++ language, with modular structure, cross-platform capabilities and efficient performance. The software mainly focuses on space geodetic data processing, precise positioning and orbit determination, and multi-source fusion navigation. With the integration of multiple space geodetic techniques at observation level, GREAT can achieve the determination of global geodetic parameters. Meanwhile, GREAT can also achieve real-time precise orbit and clock determination by processing GNSS data from globally distributed stations, and the accuracies are about 3–6 cm for orbit and 0.1–0.4 ns for clock. Based on high-precision orbit and clock products, centimeter-level onboard positioning accuracies can be achieved with PPP-RTK in open-sky scenarios. Furthermore, centimeter-level multi-source fusion navigation can be achieved in urban scenarios though the integrated system of PPP-RTK/MEMS/VIS/LiDAR. Additionally, efficiency optimization algorithms such as parallel computing are applied to enable the software to handle the data-intensive and calculation-intensive situations.

Space Geodetic Insights to the Dramatic Stress Rotation Induced by the February 2023 Turkey‐Syria Earthquake Doublet

AbstractThe February 2023 Turkey‐Syria Earthquake doublet ruptured multiple segments of the East Anatolian Fault (EAF) Zone. Dominating seismicity focal mechanism shifted dramatically from strike‐slip to normal‐faulting after the doublet. To better understand this shift, here we derived a comprehensive 3D co‐seismic displacement field and performed the stress analysis. Abundant space geodetic data were used to generate high‐resolution 3D surface displacement, which provide tight constraints on fault geometry, slip distribution and stress field. Together with stress inversion from aftershock focal mechanisms, we show that the principal stress direction rotation in the region with the most normal‐faulting aftershocks is the staggering 29°. The induced heterogenous stress may explain the shift of the dominant focal mechanism toward normal faulting. We suggest that the extensional horsetail splay faults, likely formed through geologic time scale related to the releasing bend on the EAF, are the hosts of most of the normal faulting aftershocks.

Rupture Geometry and Slip Distribution of the Mw 7.2 Nippes Earthquake, Haiti, From Space Geodetic Data

AbstractOn 14 August 2021 the Mw 7.2 Nippes earthquake struck southern Haiti, rupturing a segment of the Enriquillo‐Plantain Garden Fault system (EPGF), a 300 km‐long strike‐slip fault system that accommodates half of the highly oblique convergence displacement between the Caribbean and the North American plates. We use coseismic surface displacements from Interferometric Synthetic Aperture Radar and Global Navigation Satellite System (GNSS) to estimate the geometry of the rupture through a systematic parametric exploration, determine its mechanism, and relate them to the regional tectonics derived from interseismic GNSS measurements. We show that the earthquake ruptured a north dipping fault (66 ± 4° dip) with a geodetically determined moment release that is 40% reverse and 60% strike‐slip. We cannot conclude whether this north‐dipping structure is the EPGF itself or a distinct fault running parallel to the EPGF. The rupture then evolved to the west on a vertical (86 ± 2° dip) fault parallel to the EPGF, the Ravine du Sud fault, with left‐lateral strike‐slip motion. The coseismic slip distribution of the 2010 Léogane and 2021 Nippes earthquakes, consistent with the transpressional interseismic strain rate field, show a segmentation of the Caribbean–North American plate boundary in southern Haiti and imply a revision in our understanding of the mode of earthquake rupture within the EPGF system.

Space Geodetic Data and Fault model for the 2021 Nippes Earthquake, Haiti

Space Geodetic Data and Fault model for the 2021 Nippes Earthquake, Haiti

Space Geodetic Data and Fault model for the 2021 Nippes Earthquake, Haiti

Space Geodetic Data and Fault model for the 2021 Nippes Earthquake, Haiti

Space Geodetic Data and Fault model for the 2021 Nippes Earthquake, Haiti

Space Geodetic Data and Fault model for the 2021 Nippes Earthquake, Haiti

Coseismic and early post-seismic deformations due to the 2019 earthquake sequence in Ridgecrest, California

SUMMARYThe 2019 Ridgecrest earthquake sequence in the Mojave Desert that ruptured a complex orthogonal conjugate fault system offers a rare opportunity to probe the mechanics of the intraplate lithosphere of the central eastern California shear zone (ECSZ). We used space geodetic data to investigate the coseismic and post-seismic deformations attributable to this earthquake sequence. A triangular dislocation inversion scheme was used to derive the coseismic and post-seismic slip distributions on five non-planar faults in a homogeneous elastic crust. A wide range of viscoelastic relaxation models with varying upper mantle viscosities were also tested to constrain the rheological structure. The inferred coseismic slip exhibited a pronounced (approximately 60 per cent) shallow slip deficit (SSD), only a small proportion of which was recovered by early aseismic afterslip. Inversions of GPS and InSAR data suggest that the near-field post-seismic transient was dominated by afterslip at depths of 3–8 km. Viscosity modelling yielded a robust lower bound of approximately 8.0 × 1017 Pa s on the viscosity of the upper mantle. Both the GPS observations and the modelled viscosity at each individual station showed a lateral heterogeneous relaxation process on both northeast and southwest ECSZ. The effective viscosity of the mantle asthenosphere to the northeast was inferred to be approximately two times lower than that to the southwest, which is consistent with the pattern expected for regional heat flow. A comparison among the static coseismically induced Coulomb stress changes, the cumulative distribution of aftershocks and the afterslip distribution suggests that aftershocks and shallow afterslip could be responses to coseismically induced stresses, but the aftershock and afterslip distribution are poorly correlated. We argue that the pronounced SSD and lack of shallow afterslip during the Ridgecrest earthquake sequence are indicative of an immature fault. Furthermore, we suggest similar rheological structures for the southern and central ECSZ and infer a relatively low effective viscosity for the mantle to the northeast because of its high heat flow. We also propose that the afterslip may illuminate the rate-strengthening regions that mostly slip aseismically, but the aftershocks may illuminate fluid-saturated areas near ruptures.

Geometric estimates of variations in space geodetic data

Well-known statistical parameters have some disadvantages when analyzing space geodetic data. Geometric parameters are proposed here for estimating the variation properties of samples for various discrete datasets. The proposed parameters are logically related to each other and are based on the simplest well-known statistical parameters; they do not depend on the type of distribution of the sample under study. “Variation asymmetry” shows the shift of the arithmetic mean relative to the center of the variation interval in the units of the studied sample. “Density of variation” characterizes the level of average variability in sample units. This parameter has several times greater discriminatory sensitivity to extremely different types of variations than linear and standard deviations. The relative parameter “proportion of maximum density” shows the closeness of variation to a uniform distribution in the ranked sample and complements the indicator of variation density. An algorithm for separating different structural levels of the useful signal from emissions (noise) is proposed here based on the calculation of geometric characteristics. The iterations of dividing the sample into structurally homogeneous segments can be stopped at the level of the proportion of maximum density ≥0.9 when analyzing real GPS coordinates.

Tehri Reservoir Operation Modulates Seasonal Elastic Crustal Deformation in the Himalaya

AbstractThe filling and emptying cycles of reservoir operations may change hydrological mass loading, leading to a flexural deformation of the crust that may compromise the infrastructure safety or trigger earthquakes. In this study, we investigate the seasonal crustal response of the Tehri reservoir in the Garhwal Himalaya, northern India, using interferometric synthetic aperture radar (InSAR), Global Positioning System, the Gravity Recovery and Climate Experiment, radar altimetry, and in‐situ water‐level measurements. Results show that the evolution of vertical ground deformation is modulated elastically by the reservoir operation, whereas the horizontal displacement measured near the reservoir exhibits a time lag of ∼65 days with respect to the vertical displacements and water‐level variations. The delayed deformation transients indicate that the reservoir loading/unloading cycles affect the near‐surface hydrology in its neighborhood. The broader distribution and higher amplitude of ground deformation during the loading periods revealed by the InSAR time series can be explained by water–rock interactions, which cause a decrease in the effective Young's modulus within the top 300‐m crustal layer. Our results demonstrate the potential of using space geodetic data to ensure a better understanding of the solid Earth response to regional hydrological changes.

Surge of Mangla reservoir loading promoted failure on active Décollement of western Himalayas

The extreme rainfall weather during the Indian monsoon season has increased in recent decades changing the hydrological mass distribution that may be responsible for triggering regional earthquakes. In the western Himalayas, a shallow Mw 5.7 earthquake took place right after the withdrawal of the 2019 unusual Indian summer monsoon resulting in a rapid increase of ~4.5 km3 of water storage at the nearby Mangla reservoir within three months. Through a joint inversion of space geodetic and teleseismic data, we found that the mainshock occurred on the décollement structure of the Main Himalayan Thrust in the western Himalayas, which was previously underdetermined. The significant water loading, and pore pressure diffusion led to Coulomb stress increases of ~10 kPa on the maximum coseismic slip zone promoting fault failure. Our findings demonstrate that climate change could influence certain reservoir-associated earthquakes in the Himalayas. We provide recommendations to improve the regulations for the reservoir operations in Mangla and probably other contexts with similar tectonic settings in the Himalayas during the monsoon season.

Insight into the May 2015 summit inflation event at Kīlauea Volcano, Hawai‘i

We use ground and space geodetic data to study surface deformation at Kīlauea Volcano from January to September 2015. This period includes an episode of heightened activity in April and May 2015 that culminated in a magmatic intrusion beneath the volcano's summit. The data set consists of Global Navigation Satellite System (GNSS), tilt, visual and seismic time series along with 25 descending and 15 ascending acquisitions of the Sentinel-1 satellite. We identify four different stages of surface deformation and volcanic activity, which we attribute to pressure changes and the movement of magma in response to an imbalance between magma supply and withdrawal in the shallow plumbing system, eventually leading to an intrusion beneath the summit area. In particular, we model the deformation as due to pressure changes in two subsurface magma bodies: the Halema‘uma‘u Reservoir (HMMR) and South Caldera Reservoir (SCR). The SCR was best described by an ellipsoidal source at 2.8 (2.65–3.07 at 95% confidence) km depth below the south caldera region. The HMMR was modeled as a point source located just east of Halema‘uma‘u crater at 1.5 (0.95–2.62) km depth. We suggest that a short-term increase in the magma supply rate to the volcano is a potential mechanisms for the intrusion, although other factors, like the filling of available void space or a reduced efficiency of magma transport through the volcano's East Rift Zone, may also play a role.

Joint adjustment for large-area, multi-source vertical data: method, validation and application

In order to reveal the residual distribution pattern and obtain a wide range of high-accurate vertical movement field, we systematically analyzed the joint geodetic adjustment with vertical rate parameters (denoted as joint adjustment) issues based on the simulated and actual multi-source vertical data. First of all, 1000 sets of simulated leveling data containing rand noise were constructed and processed. The corresponding adjustment results show that network shape and observation interval are two main factors affecting the reliability of the vertical rates. Particularly, vertical rates of the small loops, internal points and loops with longer intervals are prior to those of large loops, edge points and loops with short intervals, respectively. Subsequently, we developed a Helmert adjustment program, which can jointly process leveling data and space geodetic data. Compared with the single leveling data adjustment (SLDA), the joint adjustment results of leveling data and 500 geodetic observations (including 2–4 mm/yr errors) demonstrate that the Helmert adjustment can reduce the residual distribution range by roughly 46%. Finally, both SLDA and Helmert methods are applied to actual survey data in eastern China. We find that the error of the latter approach is decreased by about 48% compared with the former. In summary, the Helmert adjustment method can significantly improve the reliability and accuracy of vertical movement in large area.

Rupture kinematics of 2020 January 24 Mw 6.7 Doğanyol-Sivrice, Turkey earthquake on the East Anatolian Fault Zone imaged by space geodesy

SUMMARYHere, we present the results of a kinematic slip model of the 2020 Mw 6.7 Doğanyol-Sivrice, Turkey Earthquake, the most important event in the last 50 yr on the East Anatolian Fault Zone. Our slip model is constrained by two Sentinel-1 interferograms and by 5 three-component high-rate GNSS (Global Navigation Satellite System) recordings close to the earthquake source. We find that most of the slip occurs predominantly in three regions, two of them at between 2 and 10 km depth and a deeper slip region extending down to 20 km depth. We also relocate the first two weeks of aftershocks and find a distribution of events that agrees with these slip features. The HR-GNSS recordings suggest a predominantly unilateral rupture with the effects of a directivity pulse clearly seen in the waveforms and in the measure peak ground velocities. The slip model supports rupture propagation from northeast to southwest at a relatively slow speed of 2.2 km s−1 and a total source duration of ∼20 s. In the absence of near-source seismic stations, space geodetic data provide the best constraint on the spatial distribution of slip and on its time evolution.

Finite Slip Models of the 2019 Ridgecrest Earthquake Sequence Constrained by Space Geodetic Data and Aftershock Locations

ABSTRACTThe July 2019 Ridgecrest, California, earthquake sequence involved two large events—the M 6.4 foreshock and the M 7.1 mainshock that ruptured a system of intersecting strike-slip faults. We present analysis of space geodetic observations including Synthetic Aperture Radar and Global Navigation Satellite System data, geological field mapping, and seismicity to constrain the subsurface rupture geometry and slip distribution. The data render a complex pattern of faulting with a number of subparallel as well as cross-cutting fault strands that exhibit variations in both strike and dip angles, including a “flower structure” formed by shallow splay faults. Slip inversions are performed using both homogeneous and layered elastic half-space models informed by the local seismic tomography data. The inferred slip distribution suggests a moderate amount of the shallow coseismic slip deficit. The peak moment release occurred in the depth interval of 3–4 km, consistent with results from previous studies of major strike-slip earthquakes, and the depth distribution of seismicity in California. We use the derived slip models to investigate stress transfer and possible triggering relationships between the M 7.1 mainshock and the M 6.4 foreshock, as well as other moderate events that occurred in the vicinity of the M 7.1 hypocenter. Triggering is discouraged for the average strike of the M 7.1 rupture (320°) but encouraged for the initial orientation of the mainshock rupture suggested by the first-motion data (340°). This lends support to a scenario according to which the earthquake rupture nucleated on a small fault that was more optimally oriented with respect to the regional stress and subsequently propagated along the less-favorably oriented pre-existing faults, possibly facilitated by dynamic weakening. The nucleation site of the mainshock experienced positive dynamic Coulomb stress changes that are much larger than the static stress changes, yet the former failed to initiate rupture.

Geostatistical evaluation of spatial variability of land subsidence rates in Lagos, Nigeria

Accurate land subsidence prediction is fundamental for effective management of land subsidence and other associated geohazards. Lagos, the most densely populated city in Nigeria, has been adversely affected by widespread land subsidence. Previous studies have largely been restricted to analyzing space geodetic technique data. Unfortunately, this technique imposes spatial limitations resulting in incomplete coverage of the study areas due to atmospheric effects, orbital satellite characteristics, or surface characteristics. The application of geostatistics to georeferenced data obtained from space-based measurements can reliably provide complete information on spatial variability. The objective of this study is to provide an overview of current subsidence rates and to assess the spatial variability of land subsidence in the study area by using geostatistics that integrate semivariogram and ordinary kriging. The study area was partitioned into eight subregions; for each subregion, the experimental variogram was determined from the observed data and fitted to the optimal models. Seven subregions were fitted to exponential models and one was fitted to the spherical model. The model semivariograms were used in the kriging analysis to estimate the spatial variability of subsidence rates. The results showed that the nugget-to-sill ratio lies between 44 and 70%, indicating that the spatial variation of subsidence rates at the scale under study is moderately distributed and the mechanism of deformation is similar. The nugget effect of the subsidence rate is between 0.25 and 0.75, indicating that subsidence rates are influenced by various contributions. The predicted spatial variability of subsidence rates by Ordinary Kriging presents reliable values of R-squared (0.32–0.42) and RMSE (0.21–0.30). Critical subsidence rates characterised the areas around the Atlantic Ocean coastal alluvium deposit, the Lagos lagoon, and the Ogun River flood alluvium. This study successfully demonstrates the suitability of the geostatistical tools to evaluate spatial variability of subsidence rates.

Improved Global Nonlinear Surface Mass Variation Estimates From Geodetic Displacements and Reconciliation With GRACE Data

AbstractSpatiotemporal coverage gaps and the nature of distant signature sources in Global Navigation Satellite System (GNSS) and The Gravity Recovery and Climate Experiment (GRACE) data require global inversions of data combinations for cross validation and complete and continuous monitoring of surface water mass variations. For spectral completeness, accurate data‐based degree‐1 surface mass variation coefficient or equivalent geocenter motion estimates are also desired but very difficult to obtain. To improve the reliability of such estimates, we carry out a new effort to combine different space geodetic technique data in a Kalman filter and time series approach to Terrestrial Reference Frame realization using an advanced formulation. With origin at the center of mass of the Earth system, the new parameterization now includes site displacements in the state vector explicitly for realistic assessment of their covariance matrices. More robust geocenter motion results are achieved when the displacement information is combined further with GRACE gravity data in a unified inversion. Previously, various systematic effects in GNSS data resulted in rather large discrepancies in global surface mass change estimates when compared with those from GRACE gravity data. Here, we show that significantly improved GNSS data after reprocessing and the refined Estimating the Circulation and Climate of the Ocean (ECCO) bottom pressure model reveal a global surface mass variation pattern that has been largely reconciled with that from GRACE data.

Outlier-insensitive Bayesian inference for linear inverse problems (OutIBI) with applications to space geodetic data

SUMMARYInverse problems play a central role in data analysis across the fields of science. Many techniques and algorithms provide parameter estimation including the best-fitting model and the parameters statistics. Here, we concern ourselves with the robustness of parameter estimation under constraints, with the focus on assimilation of noisy data with potential outliers, a situation all too familiar in Earth science, particularly in analysis of remote-sensing data. We assume a linear, or linearized, forward model relating the model parameters to multiple data sets with a priori unknown uncertainties that are left to be characterized. This is relevant for global navigation satellite system and synthetic aperture radar data that involve intricate processing for which uncertainty estimation is not available. The model is constrained by additional equalities and inequalities resulting from the physics of the problem, but the weights of equalities are unknown. We formulate the problem from a Bayesian perspective with non-informative priors. The posterior distribution of the model parameters, weights and outliers conditioned on the observations are then inferred via Gibbs sampling. We demonstrate the practical utility of the method based on a set of challenging inverse problems with both synthetic and real space-geodetic data associated with earthquakes and nuclear explosions. We provide the associated computer codes and expect the approach to be of practical interest for a wide range of applications.

Logarithmic Model Joint Inversion Method for Coseismic and Postseismic Slip: Application to the 2017 Mw 7.3 Sarpol Zahāb Earthquake, Iran

AbstractInterferometric synthetic aperture radar (InSAR) has become an important technique for studying earthquake cycle deformation. However, due to the limited satellite revisit time, it is often difficult to fully separate coseismic and postseismic slip from InSAR data. Nevertheless, accurately estimating spatiotemporal coseismic and postseismic fault slip distribution models is important for quantifying earthquake slip, understanding the kinematics of seismogenic faulting, and evaluating seismic hazards. Here, we develop a logarithmic model‐based method (LogSIM) for the joint inversion of coseismic and postseismic fault slip using InSAR data from multiple platforms in different orbits. This method considers the nature of early postseismic slip following logarithmic decay. The coseismic slip, the decay time constant, and the decay amplitude of the logarithmic model can be jointly estimated from unwrapped interferograms without the need for InSAR time series calculations, thereby reducing the number of unknown parameters and stabilizing the inversion. The robustness of LogSIM is first validated with synthetic experiments. We then apply LogSIM to invert for the coseismic and postseismic slip models of the 2017 Mw 7.3 Sarpol Zahāb earthquake. We find that the maximum afterslip value and postseismic moment release during the first four months reported in previous studies are underestimated by ~26% and ~31%, respectively, due to the unavailability of the first five days of postseismic deformation. The estimated afterslip distribution spatially overlaps with the aftershocks in the updip region of the fault plane. LogSIM could potentially be extended to integrate different space geodetic data in earthquake cycle deformation modeling.

Modeling 3D Free-geometry Volumetric Sources Associated to Geological and Anthropogenic Hazards from Space and Terrestrial Geodetic Data

Recent decades have shown an explosion in the quantity and quality of geodetic data, mainly space-based geodetic data, that are being applied to geological and anthropogenic hazards. This has produced the need for new approaches for analyzing, modeling and interpreting these geodetic data. Typically, modeling of deformation and gravity changes follows an inverse approach using analytical or numerical solutions, where normally regular geometries (point sources, disks, prolate or oblate spheroids, etc.) are assumed at the initial stages and the inversion is carried out in a linear context. Here we review an original methodology for the simultaneous, nonlinear inversion of gravity changes and/or surface deformation (measured with different techniques) to determine 3D (three-dimensional) bodies, without any a priori assumption about their geometries, embedded into an elastic or poroelastic medium. Such a fully nonlinear inversion has led to interesting results in volcanic environments and in the study of water tables variation due to its exploitation. This methodology can be used to invert geodetic remote sensing data or terrestrial data alone, or in combination.

First Field Evidence of Coseismic Land‐Level Change Associated with the 25 December 2016 Mw 7.6 Chiloé, Chile, Earthquake

Assessments of megathrust earthquake rupture patterns provide fundamental insights into the processes that control the seismic cycle along subduction zones. When large earthquakes occur in regions with sparse geodetic networks, as was the case for the magnitude (⁠ Mw ⁠) 7.6 Chiloe, Chile, earthquake of 25 December 2016, estimates of vertical coseismic deformation from fixed intertidal biotic indicators provide important evidence that help to constrain fault slip. Ten months after the Chiloe earthquake, we observed a white fringe of bleached coralline algae (Corallinaceae) along the southeastern coastline of Isla Quilan, south of Isla de Chiloe, killed by reduced tidal wetting resulting from coseismic land uplift. Our quantitative measurements of the vertical extent of algal mortality provide the first field‐based report of the effects of the 2016 earthquake. We infer Isla Quilan coseismically uplifted by 25.8±14.3 cm ⁠. The vertical extent of mortality (VEM) and the aspect (compass direction) of the bedrock surface are uncorrelated, but we find that exposure to waves and shielding from insolation may prevent or delay mortality. Focusing on sites sheltered from waves, we demonstrate that with a large number of measurements (⁠ >100 ⁠), land‐level changes as low as 25 cm may be quantitatively assessed. The absence of bleaching on Isla de Chiloe may reflect the smaller magnitude of coseismic uplift at this location or the lack of suitably sheltered bedrock surfaces. Previously published fault dislocation models are consistent with our field observations; however, the coralline algae data are on their own insufficient to discriminate between competing hypotheses over the amount of fault slip. By combining our field data with space geodetic data in a model that uses detailed fault geometry, we constrain peak slip to ∼3 m ⁠, approximately 80% of the maximum cumulative plate convergence since the last great earthquake in the region.