Geophys Res Research Articles

Retrieval and validation of the Secchi disk depth values (Zsd) from the Sentinel-3/OLCI satellite data in the Persian Gulf and the Gulf of Oman.

In this study, the Secchi disk depth (Zsd) values as an indicator of seawater clarity/transparency were estimated using the ESA (European Space Agency) Sentinel-3A and Sentinel-3B OLCI (S3/OLCI) satellite data in the Persian Gulf and the Gulf of Oman (PG&GO). To do so, two procedures were evaluated including an existing methodology developed by Doron et al. (J Geophys Res: Oceans 112(C6) 2007 and (Remote Sens Environ 115:2986-3001 2011) and an empirical model proposed in this research formed by employing the blue (B4) and green (B6) bands of S3/OLCI data. In this regard, a total number of 157 field-measured Zsd values (114 training points for calibration of the models and 43 control points for accuracy assessment of them) were observed during eight research cruises conducted by the research vessel, the Persian Gulf Explorer, in the PG&OS between 2018 and 2022. The optimum methodology was then selected based on the statistical indicators including R2 (coefficient of determination), RMSE (root mean square error), and MAPE (mean absolute percentage error). However, after the indication of the optimal model, the data of all 157 observations were utilized for the calculation of unknown parameters of the model. The final results demonstrated that compared to the existing empirical model proposed by Doron et al. (J Geophys Res: Oceans 112(C6) 2007 and (Remote Sens Environ 115:2986-3001 2011), the developed model in this study which was formed based on the linear and ratio terms of B4 and B6 bands, has more efficiency in the PG&GO. Consequently, a model in form of Zsd = e1.638B4/B6-8.241B4-12.876B6+1.26 was suggested for the estimation of Zsd values from S3/OLCI in the PG&GO (R2 = 0.749, RMSE = 2.56m, and MAPE = 22.47%). The results also showed that the annual oscillation of the Zsd values in the GO (5-18m) is evidently higher compared with those in the PG (4-12m) and the SH (7-10m) regions.

Microscale THMC Modeling of Pressure Solution in Salt Rock: Impacts of Geometry and Temperature

Pressure solution, a mechanism that involves tight coupling between the geometry and thermal-hydro-mechanical-chemical (THMC) processes, plays an important role in diagenesis. In this study, we make the first attempt to conduct microscale THMC modeling to understand and quantify the impacts of geometry and temperature on pressure solution, taking natural salt rock as an example. This modeling capability is achieved by expanding a novel MC code that we developed previously (Hu et al. J Geophys Res: Solid Earth 126:e2021JB023112, 2021) to include temperature effects. We first conduct a simulation of an example that involves a single brine inclusion within a single halite grain and find that the temperature impact is limited for that case. We then extract geometry from an image of a natural salt rock and conduct simulations with different cases: (A) only temperature and no stress, (B) only stress and no temperature, and (C) with both stress and temperature. These different cases result in quite different phenomena. In case A, dissolution and precipitation occur across the entire system due to isolated pore space reaching a localized mass balance between dissolution, precipitation, and diffusion. In case B, intense geometric features (e.g., major asperities, inclusions) in one area undergo stress concentration, thus dominating pressure solution in that area. In case C, pressure solution is spread out at contacting highly stressed geometric features close to the hotter side. We conclude that geometric features dominate stress distribution, thus dominating pressure solution in a natural salt rock that may be affected by the temperature if a sufficient temperature gradient is applied.

Recent activity and paleoseismicity of an intraplate extensional fault: the Calamocha fault (Jiloca graben, central Iberian Chain)

The Calamocha fault is an 18-km-long, NNW–SSE striking pure normal fault that moves down the northern sector of the Jiloca graben with respect to the Neogene infill of the Calatayud basin (central Iberian Chain). Its structure and kinematics are characterized by means of detailed geological mapping, morphotectonic analysis and data recording at the outcrop scale. The Calamocha fault represents the inversion of a previous contractional fault zone under the recent tensional stress field (WSW–ENE trending σ3 trajectories). The extensional activity started during the Late Pliocene (ca. 3.8 Ma), accumulating a maximum net slip of 190–230 m (long-term slip rate of 0.05–0.06 mm/a). The palaeoseismological study of three artificial exposures near Calamocha town evidenced recurrent slip during the Late Pleistocene, which proves its active character. Analysis of faulted clastic alluvial units, dated by means of optically stimulated luminescence (OSL), reveals at least eight slip events since 145.9 ± 9.1 ka, the last one being younger than 13.8 ± 0.9 ka. Only a few events represent visible accumulated displacement on the main synthetic rupture surfaces; this allows a rough estimate of the short-term slip rate (during the Late Pleistocene) of about 0.1 mm/a, faster than the long-term rate. The Calamocha fault could potentially produce a characteristic earthquake (in the sense of Schwartz and Coppersmith, J Geophys Res 89:5681–5698, 1984) with moment magnitude Mw ≈ 6.7 ± 0.3 (Mw ≈ 6.9 ± 0.3 in a scenario of activation of the whole Calamocha–Daroca fault zone), average coseismic displacement of 0.5–1.3 m and average recurrence period under 15 ka.

Reducing the risks of nuclear war to humanity

Reducing the risks of nuclear war to humanity

Consistent estimation of strain-rate fields from GNSS velocity data using basis function expansion with ABIC

Present day crustal displacement rates can be accurately observed at stations of global navigation satellite system (GNSS), and crustal deformation has been investigated by estimating strain-rate fields from discrete GNSS data. For this purpose, a modified least-square inversion method was proposed by Shen et al. (J Geophys Res 101:27957–27980, 1996). This method offers a simple formulation for simultaneously estimating smooth velocity and strain-rate fields from GNSS data, and it has contributed to clarify crustal deformation fields in many regions all over the world. However, we notice three theoretical points to be examined when we apply the method: mathematical inconsistency between estimated velocity and strain-rate fields, difficulty in objectively determining the optimal value of a hyperparameter that controls smoothness, and inappropriate estimation of uncertainty. In this study, we propose a method of basis function expansion with Akaike’s Bayesian information criterion (ABIC), which overcomes the above difficulties. Application of the two methods to GNSS data in Japan reveals that the inconsistency in the method of Shen et al. is generally insignificant, but could be clear in regions with sparser observation stations such as in islet areas. The method of basis function expansion with ABIC shows a significantly better performance than the method of Shen et al. in terms of the trade-off curve between the residual of fitting and the roughness of velocity field. The estimated strain-rate field with the basis function expansion clearly exhibits a low strain-rate zone in the forearc from the southern Tohoku district to central Japan. We also find that the Ou Backbone Range has several contractive spots around active volcanoes and that these locations well correspond to the subsidence areas detected by InSAR after the 2011 Tohoku-oki earthquake. Thus, the method of basis function expansion with ABIC would serve as an effective tool for estimating strain-rate fields from GNSS data.

Ensemble Kalman inversion: mean-field limit and convergence analysis

Ensemble Kalman inversion (EKI) has been a very popular algorithm used in Bayesian inverse problems (Iglesias et al. in Inverse Probl 29: 045001, 2013). It samples particles from a prior distribution and introduces a motion to move the particles around in pseudo-time. As the pseudo-time goes to infinity, the method finds the minimizer of the objective function, and when the pseudo-time stops at 1, the ensemble distribution of the particles resembles, in some sense, the posterior distribution in the linear setting. The ideas trace back further to ensemble Kalman filter and the associated analysis (Evensen in J Geophys Res: Oceans 99: 10143–10162, 1994; Reich in BIT Numer Math 51: 235–249, 2011), but to today, when viewed as a sampling method, why EKI works, and in what sense with what rate the method converges is still largely unknown. In this paper, we analyze the continuous version of EKI, a coupled SDE system, and prove the mean-field limit of this SDE system. In particular, we will show that 1. as the number of particles goes to infinity, the empirical measure of particles following SDE converges to the solution to a Fokker–Planck equation in Wasserstein 2-distance with an optimal rate, for both linear and weakly nonlinear case; 2. the solution to the Fokker–Planck equation reconstructs the target distribution in finite time in the linear case, as suggested in Iglesias et al. (Inverse Probl 29: 045001, 2013).

Forecasting the North Atlantic Oscillation index using altimetric sea level anomalies

The objective of this paper is to present a new approach for forecasting NAO index (NAOi) based on predictions of sea level anomalies (SLAs). We utilize significant correlations (Pearson’s r up to 0.69) between sea surface height (SSH) calculated for the North Atlantic (15–65°N, basin-wide) and winter Hurrell NAOi, as shown by Esselborn and Eden (Geophys Res Lett 28:3473–3476, 2001).We consider the seasonal and monthly data of Hurrell NAOi, ranging from 1993 to 2017. Weekly prognoses of SLA are provided by the Prognocean Plus system which uses several data-based models to predict sea level variation. Our experiment consists of three steps: (1) we calculate correlation between the first principal component (PC1) of SSH/SLA data and NAOi, (2) we determine coefficients of a linear regression model which describes the relationship between winter NAOi and PC1 of SLA data (1993–2013), (3) we build two regression models in order to predict winter NAOi (by attaching SLA forecasts and applying coefficients of the fitted regression models). The resulting 3-month prognoses of winter NAOi are found to reveal mean absolute errors of 1.5 or less. The choice of method for preparing SLA data for principal component analysis is shown to have a stronger impact on the prediction performance than the selection of SLA prediction method itself.

New Source Duration Relationships for Mexican Earthquakes: Practical Application to Stochastic Summation Methods

From the gathering of 127 source time functions (STFs) of seismic events in Mexico, relationships have been developed between the seismic moment (M0) and the total source rupture duration (τd), for normal-faulting inslab, interplate and strike-slipe mechanisms. This relationship has been explored by different authors like Furomoto and Nakanishi (J Geophys Res 88:2191–2198, 1983), Tanioka and Ruff (Seismol Res Lett 68:386–400, 1997), Singh et al. (Bull Seismol Soc Ame 90:468–482, 2000), among others; the latter authors present a similar general relationship for Mexico, considering 53 STFs and with information until 1998. In this research, complementary databases have been integrated, and the available functions updated base on recent research works about the SCARDEC method are used (Vallee et al. in Geophys J Int 184:338–358, 2011; Vallee and Douet in Phys Earth Planet Interiors 257:149–157, 2016). With the proposed expressions, it is possible to estimate reasonably, the main parameters of interest for algorithms of stochastic summation, such as the corner frequencies or stress drops in order to simulate strong ground motions, commonly used for source-rupture studies, site-amplification analysis, or for earthquake-resistant design. Besides, a new flexible model of stochastic summation is presented, which allows considering several ways to generate more realistic motions, according to the spectral behavior, both for low and for intermediate frequencies, under earthquakes with moderate and high magnitude; this model was compared with results from a two-stage alternative method considering two corner frequencies.

Modeling equatorial ionospheric vertical plasma drifts using machine learning

We present the results of an effort to model quiet-time vertical plasma drifts in the low-latitude F-region ionosphere using the random forest machine learning technique. The model is capable of describing the climatological variation of the drifts as a function of universal time, day of the year, solar flux, and altitude (200–600 km). The model has been trained using measurements of the vertical plasma drifts made by the incoherent scatter radar of the Jicamarca Radio Observatory (11.95^circ hbox { S}, 76.87^circ W, sim 1^circ dip lat). In our analysis, we compare our machine learning model results with the Scherliess and Fejer (J Geophys Res 104:6829–6842, 1999) model (SF99 model), a widely used empirical model of the vertical drifts developed using a different set of Jicamarca measurements. We find that the machine learning model is able to capture the overall features of the diurnal variation of the equatorial drifts for different seasonal and solar flux conditions. The model is also capable of capturing the mean height variation of the drifts, particularly the height gradient enhancements that have been observed near sunrise and sunset. Finally, the model can easily be expanded and improved as more drift measurements are made and become available for training.

Patterns of the Seismic Cycle in the Kuril Island Arc from GPS Observations

The 2006–2007 Simushir earthquakes started a new episode in the rupture history of the Kuril-Kamchatka subduction zone. This earthquake doublet terminated the seismic silence in the Central Kurils, which had lasted for almost a century. The analysis of seismologic, geologic and GPS data over the Kuril Islands region allows us to reveal the patterns of deformation of the lithosphere in the Kuril subduction zone, in particular, the peculiarities of accumulation and relaxation of elastic stresses during the seismic cycle. We analyzed > 9 years of continuous GPS observations on the Kuril Islands to determine the surface displacements caused by the geodynamic processes in the subduction zone. We used available GPS data to model the coseismic stress release and postseismic stress relaxation related to the 2006–2007 Simushir earthquakes. We showed that the duration of postseismic relaxation after the 2006 earthquake exceeds 10 years, preventing transition of the central Kurils to the interseismic stage and thus delaying the beginning of the new seismic cycle. The value of Maxwell viscosity of the asthenosphere found in this study (3 × 1017 Pa s) in the Kuril Island arc is substantially lower than the values determined for several other subduction zones. This contrast in viscosity agrees with Kogan et al. (J Geophys Res 118:3691–3706, 2013), who used shorter GPS time series than in our study. The results of our analysis show that multidirectional motions along the Kurils Islands are explained by the fact that segments of the island arc are at different stages of the seismic cycle.

The Subjectivity in Identification of Martian Channel Networks and Its Implication for Citizen Science Projects

The Martian surface is incised by numerous valley networks, which indicate the planet experienced sustained widespread flowing water in the past (e.g. Carr in Water on Mars, Oxford University Press, New York, 1996; Phil Trans R Soc A 370:2193–2212, 2012. https://doi.org/10.1098/rsta.2011.0500). Examining the distribution and geometries of these valley networks provides invaluable information about the Martian climate during the period of formation. The recent advancement in high resolution images has provided an opportunity to build upon past valley maps of Mars (Bahia et al. in LPSC 2018, 2018), however, the identification of these valley networks is extremely time-consuming. A citizen science project may aid in reducing this time-consuming process; this project conducts a valley mapping task with participants of varying expertise in valley mapping to determine whether a citizen science project of this kind should be worth pursuing. This was conducted in a region adjacent to Vogel Crater (36.1° S, 10.2° W). Repeated mapping of the area (a repeatability test) found that participants with low experience in valley mapping (22 a-level physics student’s representative of the public) were inconsistent when mapping valleys. Additionally, when comparing the results of participants within this group (a reproducibility test), the majority of reproduced valleys are false positives (i.e. incorrectly traced valleys). These results were consistent with those found for the medium experience group (45 2nd year geology undergraduates). The validated tracings of the low experience group improve upon the number and total length of valleys mapped by previous studies (Hynek et al. in J Geophys Res 115:1–14, 2010). To validate these valleys requires the input of an expert to remove false positives which is less time consuming than manually mapping the images; this may indicate that a citizen science project is worth pursuing. However, to effectively identify the maximum amount of valleys an expert is required.

The energetics of internal tides at the Luzon Ridge

Three-dimensional simulations of the M2 and K1 internal tides using the MIT General Circulation Model (MITgcm) configured for the Luzon Ridge are presented. The energetics of M2 and K1 internal tides are studied by analyzing the full barotropic and baroclinic energy budgets and the barotropic and baroclinic kinetic energy budgets. The conversion rate of M2 tide is also investigated using the approximate expression by Nycander (J Geophys Res 110:C10028, 2005). The results show that about 15.10 GW is transferred from the M2 barotropic tide to the M2 baroclinic tide at the Luzon Ridge, which is about 88% of the loss by the barotropic tide. The net baroclinic energy flux is about 4.46 GW, and the total dissipation is about 11.33 GW. Additionally, it is found that the potential energy changes are small in the full energy budget when comparing the result between the full barotropic and baroclinic energy budgets and the barotropic and baroclinic kinetic energy budgets. The expression by Nycander (J Geophys Res 110:C10028, 2005) is found to be sensitive to the model resolution, but may underestimate the conversion rate at the Luzon Ridge at high resolution compared with the model results.

Implementation of snow albedo schemes of varying complexity and their performances in offline Noah and Noah coupled with NCEP CFSv2

The representation of snow albedo in global models is recognized as one of the key sources of uncertainty in the simulation of mean and variability of climate. The Climate Forecast System version 2 (CFSv2), which is used for subseasonal-to-seasonal forecast of weather and climate, also suffers from large overestimation of surface albedo, particularly over the snow region. In order to improve the snow albedo biases, performances of three snow albedo schemes: the existing ‘maximum snow albedo’ (MSA) scheme of land surface model Noah, temperature dependent scheme of Roeckner et al. (The atmospheric general circulation model ECHAM5—part 1. Technical Report 349, Max Planck Institute for Meteorology, 2003) (RK03) and prognostic albedo scheme of Dutra et al. (J Hydrometeor 11:899–916, 2010) (DU10) are evaluated in offline mode. While offline Noah performs better with MSA scheme as compared to RK03 and DU10 in simulating climatological mean albedo, DU10 scheme shows a better skill in simulating monthly albedo and also captures the interannual variability with high fidelity. Therefore, MSA and DU10 schemes are also evaluated in coupled model along with the existing albedo scheme of Briegleb (J Geophys Res 97:7603–7612, 1992) (BR92) in CFSv2. The performance of MSA scheme is found to be better in simulating surface albedo, snow water equivalent and 2 m air temperature as compared to those using DU10 and BR92 schemes. Furthermore, the improved albedo have positive impact in the simulation of Indian summer monsoon rainfall, that reduces the dry bias over the Indian subcontinent, and cold bias in sea surface temperature and improves rainfall teleconnection. Thus, among four schemes (MSA, RK03, DU10 and BR92) evaluated here, MSA appears to be the most suitable snow albedo scheme for CFSv2.

Analysis of dust wet deposition in the mid-latitudes of the Northern Hemisphere

Wet deposition is the efficient removal process for fine dust aerosol. Dust wet deposition in the mid-latitudes of the Northern Hemisphere is investigated in this study by analyzing the dust simulations with the Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model, measurements from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and the meteorological and hydrological fields from Modern Era-Retrospective Analysis for Research and Applications (MERRA) reanalysis. The dust aerosol optical depth (AOD) and dust extinction coefficient from CALIPSO observation and GOCART simulation, in conjunction with the wind field from MERRA, show that the dust plume extending eastward from Asia to Pacific in the mid-latitudes becomes strongest in spring, while Taklamakan, Sahara, and Gobi dust are the main components and distribute vertically in the upper, middle, and lower parts of the dust layer across North Pacific, respectively. The wet deposition of dust in the mid-latitudes is mainly in the large-scale wet removal process, which becomes strongest in spring. The occurrence of wet deposition is accompanied by dust loading or transport. The comparison of wet deposition from GOCART simulation with the cloud water mixing ratio and precipitation production rate from MERRA indicated that wet deposition is mainly related to the water amount in ice cloud, and has a positive relationship with the precipitation in ice cloud layer. On the other hand, over arid and semiarid regions in central and eastern Asia with high dust loading, the absence of cloud water caused by the semidirect effect of dust (Huang et al., Geophys Res Lett 33(19), 2006b), can lower the amount of wet deposition. The comparison of wet deposition from GOCART simulation with the cloud water mixing ratio and vertical pressure velocity from MERRA demonstrates that a large-scale dynamic process, the ascending motion in the subpolar low-pressure system over the North Pacific, can increase the water amount in cloud and cause much more wet deposition of dust, which explains the occurrence of the largest wet deposition over the North Pacific.

Declustering of Iran earthquake catalog (1983–2017) using the epidemic-type aftershock sequence (ETAS) model

The main goal of this article is to decluster Iranian plateau seismic catalog by the epidemic-type aftershock sequence (ETAS) model and compare the results with some older methods. For this purpose, Iranian plateau bounded in 24°–42°N and 43°–66°E is subdivided into three major tectonic zones: (1) North of Iran (2) Zagros (3) East of Iran. The extracted earthquake catalog had a total of 6034 earthquakes (Mw > 4) in the time span 1983–2017. The ETAS model is an accepted stochastic approach for seismic evaluation and declustering earthquake catalogs. However, this model has not yet been used to decluster the seismic catalog of Iran. Until now, traditional methods like the Gardner and Knopoff space–time window method and the Reasenberg link-based method have been used in most studies for declustering Iran earthquake catalog. Finally, the results of declustering by the ETAS model are compared with result of Gardner and Knopoff (Bull Seismol Soc Am 64(5):1363–1367, 1974), Uhrhammer (Earthq Notes 57(1):21, 1986), Gruenthal (pers. comm.) and Reasenberg (Geophys Res 90:5479–5495, 1985) declustering methods. The overall conclusion is difficult, but the results confirm the high ability of the ETAS model for declustering Iranian earthquake catalog. Use of the ETAS model is still in its early steps in Iranian seismological researches, and more parametric studies are needed.

On the Importance of Thermo-elastic Stressing in Injection-Induced Earthquakes

The sustainability of geothermal fields is based on a paradox. On one side, fractures are targeted on heat-flow improvement, and on the other side, the same fractures are avoided because of induced seismicity risk. In this context, we developed analytical approaches for estimating (1) thermo–poro-elastic stresses in a fractured geothermal system, and (2) seismicity rates based on the model of Dieterich (J Geophys Res 99:2601–2618, 1994). We modeled cold water injected at a constant rate into a single fracture surrounded by hot impermeable layers. The rationale for focusing on one single isolated fracture was that flow in the vicinity of injection wells is often concentrated in a couple of fractures instead of being homogeneously distributed. Heat flow appeared to be dominated by advection inside the fracture and conduction outside it. Poro- and thermo-elastic stresses around the single fracture were estimated separately following two independent analytical approaches; and for any potential fault around the single fracture, the induced Coulomb stress rates were resolved. The role of thermal stresses appeared to be the leading one. We show that thermal-stressing rates can induce an increase in the rate of seismicity of more than a 1000-fold at distances up to 200 m from the single fracture. Our fast forward models are suitable for data assimilation and they open the route for heat-flow optimization while keeping seismicity at a relatively low magnitude.

Comparison of the Uniaxial Compressive Strength of the Belencito Claystone Under Stress Control and Suction Control Paths

The uniaxial compressive strength of Belencito claystone was studied through stress control and suction control path tests. Short-term uniaxial compression tests on conditioned specimens at different values of suction and long-term hydro-mechanical tests using a climatic box were performed. Volumetric deformation data and acoustic emission measurements from the short-term tests were used to determine σCD (crack damage stress threshold). Regardless of the level of suction, the σCD threshold occurred between 70 and 83% of the σpeak.short-term. The experimental results confirmed that the interpretation made by Brace and Bombolakis (J Geophys Res 68:3709–3713, 1963) and Bieniawski (Int J Rock Mech Min Sci 4:395–406, 1967) regarding long-term and short-term rock strength remains valid when considering the hydro-mechanical behaviour.

Direct evidence of surface exposed water ice in the lunar polar regions.

Water ice may be allowed to accumulate in permanently shaded regions on airless bodies in the inner solar system such as Mercury, the Moon, and Ceres [Watson K, et al. (1961) J Geophys Res 66:3033-3045]. Unlike Mercury and Ceres, direct evidence for water ice exposed at the lunar surface has remained elusive. We utilize indirect lighting in regions of permanent shadow to report the detection of diagnostic near-infrared absorption features of water ice in reflectance spectra acquired by the Moon Mineralogy Mapper [M (3)] instrument. Several thousand M (3) pixels (∼280 × 280 m) with signatures of water ice at the optical surface (depth of less than a few millimeters) are identified within 20° latitude of both poles, including locations where independent measurements have suggested that water ice may be present. Most ice locations detected in M (3) data also exhibit lunar orbiter laser altimeter reflectance values and Lyman Alpha Mapping Project instrument UV ratio values consistent with the presence of water ice and also exhibit annual maximum temperatures below 110 K. However, only ∼3.5% of cold traps exhibit ice exposures. Spectral modeling shows that some ice-bearing pixels may contain ∼30 wt % ice that is intimately mixed with dry regolith. The patchy distribution and low abundance of lunar surface-exposed water ice might be associated with the true polar wander and impact gardening. The observation of spectral features of H2O confirms that water ice is trapped and accumulates in permanently shadowed regions of the Moon, and in some locations, it is exposed at the modern optical surface.

Equation of state of solid Ne inter-calibrated with the MgO, Au, Pt, NaCl-B2, and ruby pressure scales up to 130 GPa

ABSTRACTWe measured the unit-cell volume of thermally annealed solid Ne at 30–130 GPa, which is loaded together with MgO and Pt or Au in diamond-anvil cells. Laser annealing significantly reduced the deviatoric stress and the data scatter. We fit our data to the 3rd-order Birch–Murnaghan and Vinet equations of state (EOS) with the MgO pressure scale from [Ye Y, Prakapenka V, Meng Y, Shim SH. J Geophys Res. 2017;122:3450] (hereafter MgO-Y17 scale). In order to make consistent comparison, we converted the pressures of the reported datasets for isothermal compression on Ne, so that they are consistent with the MgO-Y17 scale. The discrepancy among different datasets reduces significantly after pressure conversion. We also identified the internally consistent EOSs of Ne, MgO, Pt, Au and NaCl-B2, together with the ruby scale. Our findings contribute to internally consistent comparison of different experimental datasets on the pressure-dependent behaviors of materials.

Hydrology signal from GRACE gravity data in the Nelson River basin, Canada: a comparison of two approaches

The Gravity Recovery and Climate Experiment (GRACE) satellite mission measures the combined gravity signal of several overlapping processes. A common approach to separate the hydrological signal in previous ice-covered regions is to apply numerical models to simulate the glacial isostatic adjustment (GIA) signals related to the vanished ice load and then remove them from the observed GRACE data. However, the results of this method are strongly affected by the uncertainties of the ice and viscosity models of GIA. To avoid this, Wang et al. (Nat Geosci 6(1):38–42, 2013. https://doi.org/10.1038/NGEO1652; Geodesy Geodyn 6(4):267–273, 2015) followed the theory of Wahr et al. (Geophys Res Lett 22(8):977–980, 1995) and isolated water storage changes from GRACE in North America and Scandinavia with the help of Global Positioning System (GPS) data. Lambert et al. (Postglacial rebound and total water storage variations in the Nelson River drainage basin: a gravity GPS Study, Geological Survey of Canada Open File, 7317, 2013a, Geophys Res Lett 40(23):6118–6122, https://doi.org/10.1002/2013GL057973, 2013b) did a similar study for the Nelson River basin in North America but applying GPS and absolute gravity measurements. However, the results of the two studies in the Nelson River basin differ largely, especially for the magnitude of the hydrology signal which differs about 35%. Through detailed comparison and analysis of the input data, data post-processing techniques, methods and results of these two works, we find that the different GRACE data post-processing techniques may lead to this difference. Also the GRACE input has a larger effect on the hydrology signal amplitude than the GPS input in the Nelson River basin due to the relatively small uplift signal in this region. Meanwhile, the influence of the value of alpha , which represents the ratio between GIA-induced uplift rate and GIA-induced gravity-rate-of-change (before the correction for surface uplift), is more obvious in areas with high vertical uplift, but is smaller in the Nelson River basin. From Gaussian filtering of simulated data, we found that the magnitude of the peak gravity signal value can decrease significantly after Gaussian filtering with large average radius filter, but the effect in the Nelson River basin is rather small. More work is needed to understand the effect of amplitude restoration in the post-processing of GRACE g-dot signal. However, it is encouraging to find that both the methodologies of Wang et al. (2013, 2015) and Lambert et al. (2013a, b) can produce very similar results if their inputs are the same. This means that their methodologies can be applied to study the hydrology in other areas that are also affected by GIA provided that the effects of post-processing of their inputs are under control.