Vertical Surface Displacements Research Articles

Persistent Scatterer Interferometry for Pettimudi (India) Landslide Monitoring using Sentinel-1A Images

The continuous monitoring of land surface movement over time is of paramount importance for assessing landslide triggering factors and mitigating landslide hazards. This research focuses on measuring horizontal and vertical surface displacement due to a devastating landslide event in the west-facing slope of the Rajamala Hills, induced by intense rainfall. The landslide occurred in Pettimudi, a tea-plantation village of the Idukki district in Kerala, India, on August 6–7, 2020. The persistent-scatterer synthetic aperture radar interferometry (PSInSAR ) technique, along with the Stanford Method for Persistent Scatterers (StaMPS), was applied to investigate the land surface movement over time. A stack of 20 Sentinel-1A single-look complex images (19 interferograms) acquired in descending passes was used for PSInSAR processing. The line-of-sight (LOS ) displacement in long time series, and hence the average LOS velocity, was measured at each measurement-point location. The mean LOS velocity was decomposed into horizontal east–west (EW ) and vertical up–down velocity components. The results show that the mean LOS, EW, and up–down velocities in the study area, respectively, range from –18.76 to +11.88, –10.95 to +6.93, and –15.05 to +9.53 mm/y, and the LOS displacement ranges from –19.60 to +19.59 mm. The displacement values clearly indicate the instability of the terrain. The time-series LOS displacement trends derived from the applied PSInSAR technique are very useful for providing valuable inputs for disaster management and the development of disaster early-warning systems for the benefit of local residents.

Diffuse Deformation and Surface Faulting Distribution from Submetric Image Correlation along the 2019 Ridgecrest, California, Ruptures

ABSTRACT The 2019 Mw 6.4 and 7.1 Ridgecrest, California, earthquake sequence (July 2019) ruptured consecutively a system of high-angle strike-slip cross faults (northeast- and northwest-trending) within 34 hr. The complex rupture mechanism was illuminated by seismological and geodetic data, bringing forward the issue of the interdependency of the two fault systems both at depth and at the surface, and of its effect on the final surface displacement pattern. Here, we use high-resolution (WorldView and Pleiades) optical satellite image correlation to measure the near-fault horizontal and vertical surface displacement fields at 0.5 m ground resolution for the two earthquakes. We point out significant differences with previous geodetic- and geologic-based measurements, and document the essential role of distributed faulting and diffuse deformation in producing the observed surface displacement patterns. We derive strain fields from the horizontal displacement maps, and highlight the predominant role of rotation and shear strain in the surface rupture process. We discuss the segmentation of the rupture based on the fault geometry and along-strike slip variations. We also image several northeast-trending faults with similar orientation to the deeply embedded shear fabric identified in aftershock studies, and show that these cross faults are present all along the rupture, including at a scale <100 m. Finally, we compare our results to kinematic slip inversions, and show that the surface diffuse deformation is primarily associated with areas of shallow slip deficit; however, this diffuse deformation cannot be explained using elastic modeling. We conclude that inelastic processes play an important role in contributing to the total surface deformation associated with the 2019 Ridgecrest sequence.

Geomorphology and InSAR-Tracked Surface Displacements in an Ice-Rich Yedoma Landscape

Ice-ridge Yedoma terrain is susceptible to vertical surface displacements by thaw and refreeze of ground ice, and geomorphological processes of mass wasting, erosion and sedimentation. Here we explore the relation between a 3 year data set of InSAR measurements of vertical surface displacements during the thaw season, and geomorphological features in an area in the Indigirka Lowlands, Northeast Siberia. The geomorphology is presented in a geomorphological map, based on interpretation of high resolution visible spectrum satellite imagery, field surveys and available data from paleo-environmental research. The main landforms comprise overlapping drained thaw lake basins and lakes, erosion remnants of Late Pleistocene Yedoma deposits, and a floodplain of a high-sinuosity anastomosing river with ancient river terrace remnants. The spatial distribution of drained thaw lake basins and Yedoma erosion remnants in the study area and its surroundings is influenced by neotectonic movements. The 3 years of InSAR measurement include 2 years of high snowfall and extreme river flooding (2017–2018) and 1 year of modest snowfall, early spring and warm summer (2019). The magnitude of surface displacements varies among the years, and show considerable spatial variation. Distinct spatial clusters of displacement trajectories can be discerned, which relate to geomorphological processes and ground ice conditions. Strong subsidence occurred in particular in 2019. In the wet year of 2017, marked heave occurred at Yedoma plateau surfaces, likely by ice accumulation at the top of the permafrost driven by excess precipitation. The spatial variability of surface displacements is high. This is explored by statistical analysis, and is attributed to the interaction of various processes. Next to ground ice volume change, also sedimentation (peat, colluvial deposition) and shrinkage or swelling of soils with changing water content may have contributed. Tussock tundra areas covered by the extreme 2017 and 2018 spring floods show high subsidence rates and an increase of midsummer thaw depths. We hypothesize that increased flood heights along Siberian lowland rivers potentially induce deeper thaw and subsidence on floodplain margins, and also lowers the drainage thresholds of thaw lakes. Both mechanisms tend to increase floodplain area. This may increase CH4 emission from floodplains, but also may enhance carbon storage in floodplain sedimentary environments.

Calculation of Average Reservoir Pore Pressure Based on Surface Displacement Using Image-To-Image Convolutional Neural Network Model

The average pore pressure during oil formation is an important parameter for measuring the energy required for the oil formation and the capacity of injection–production wells. In past studies, the average pore pressure has been derived mainly from pressure build-up test results. However, such tests are expensive and time-consuming. The surface displacement of an oilfield is the result of change in the formation pore pressure, but no method is available for calculating the formation pore pressure based on the surface displacement. Therefore, in this study, the vertical displacement of the Earth’s surface was used to calculate changes in reservoir pore pressure. We employed marker-stakes to measure ground displacement. We used an improved image-to-image convolutional neural network (CNN) that does not include pooling layers or full-connection layers and uses a new loss function. We used the forward evolution method to produce training samples with labels. The CNN completed self-training using these samples. Then, machine learning was used to invert the surface vertical displacement to change the pore pressure in the oil reservoir. The method was tested in a block of the Sazhong X development zone in the Daqing Oilfield in China. The results showed that the variation in the formation pore pressure was 83.12%, in accordance with the results of 20 groups of pressure build-up tests within the range of the marker-stake measurements. Thus, the proposed method is less expensive, and faster than existing methods.

SChina20: A Stable Geodetic Reference Frame for Ground Movement and Structural Deformation Monitoring in South China

We have established a stable regional geodetic reference frame, designated as SChina20, using approximately 10-year observations (2010–2019) at 40 Global Navigation Satellite System (GNSS) sites in South China. The regional reference frame is tied to the International GNSS Service (IGS) Reference Frame 2014 (IGS14) at epoch 2020.0. The primary products from this study are seven parameters for transforming the positional time series from IGS14 to SChina20 and a seasonal model for predicting vertical land surface displacements in South China. The frame stability of SChina20 is 0.4 mm/year in all three directions. We suggest that the scope of usage of SChina20 is spatially limited to the South China region and temporally limited to the 25-year time window from 2000 to 2025. We have also established a local-scale reference frame for the Hong Kong–Zhuhai–Macau (HZM) area, designated as HZM20. Applications of SChina20 in delineating urban subsidence and landslide are demonstrated in this article. SChina20 will be updated every few years to mitigate degradation of the frame stability over time and to synchronize with future updates of the IGS reference frame.

Three-Dimensional Surface Displacement of the Eastern Beijing Plain, China, Using Ascending and Descending Sentinel-1A/B Images and Leveling Data

Surface displacement is an common environmental geological phenomenon in the Beijing Plain. Research on surface displacement in the Beijing Plain has mainly focused on vertical surface displacement, whereas the horizontal displacement has scarcely been studied. To investigate the 3-D surface displacement in the Beijing Plain, we construct a leveling-constrained multidirectional PS-InSAR 3-D surface displacement estimation method to obtain the 3-D surface displacement information. The results show that the surface displacement in the study area during 2016–2018 was mainly vertical displacement with two main northern and southern subsidence centers; the vertical displacement ranged from −150 mm/year (down) to 5 mm/year (up), and the east–west horizontal displacement ranged from 20 mm/year (east) to 22 mm/year (west). Validation results show that the 3-D surface displacement estimation results agree well with leveling data and GPS data, indicating the reliability of the 3-D surface displacement datasets. The 3-D surface displacement results show that horizontal displacement is obvious in the areas with a large vertical displacement in the eastern Beijing Plain. Additionally, the horizontal displacement is directed toward the center of vertical displacement. The compressive strain is observed close to the centers of vertical displacement, whereas tensile strain occurs far from the centers of vertical displacement. The main cause of the 3-D surface displacement in the study area is the long-term groundwater overexploitation, especially deep groundwater exploitation. The spatial and temporal extents of displacement do not exactly match the locations of the groundwater sinks in different aquifers; instead, geological structures and stratigraphic/lithological conditions may have a combined effect. Moreover, the spatial and temporal distributions of surface displacement are closely related to ground fissure activity, and both influence each other.

Time Series InSAR Three-Dimensional Displacement Inversion Model of Coal Mining Areas Based on Symmetrical Features of Mining Subsidence

The three-dimensional (3-D) displacements of mining areas is the basis of studying the mining subsidence law and obtaining surface movement parameters. The traditional multi-temporal interferometry synthetic aperture radar (InSAR) technology can only obtain the surface deformation in line-of-sight (LOS) direction, even if some methods can obtain the 3-D displacements of mining area based on InSAR. However, it has high data requirements for data types, which are not conducive to the inversion of 3-D displacements. In this paper, the symmetry of the surface basin caused by mining subsidence under different mining degrees is analyzed. According to the basic symmetrical features of mining subsidence—that the surface vertical displacement and horizontal displacement in near horizontal coal seam is symmetrical with respect to the main section of the basin, combined with time series InSAR technology (TS-InSAR)—a novel method for retrieving the 3-D displacement results from a single-geometry InSAR dataset based on symmetrical features (hereafter referred to as the SGI-SF method) is proposed. The SGI-SF method first generates multi-temporal observations of LOS displacement from a single-geometry InSAR dataset, and then transforms them into multi-temporal observations of 3-D displacement datasets according to symmetrical features. There is no necessity to obtain the surface movement parameters from the measured data to calculate 3-D displacement fields. Finally, the time series of 3-D displacements are estimated from multi-temporal 3-D displacements using the singular value decomposition (SVD) method. Nine descending Sentinel-1 images from the Yulin mining area of China are used to test the proposed SGI-SF method. The results show that the average root mean square errors (RMSE) in the vertical and horizontal direction of the three-dimensional deformations are approximately 9.28 mm and 13.10 mm, respectively, which are much smaller than mining-induced displacements and can provide support for deformation monitoring in mining areas.

Influences of buried depth and grain size distribution on seepage erosion in granular soils around tunnel by coupled CFD-DEM approach

For tunnels built in the saturated silty sand ground, fine particles may be migrated into tunnels through seams of tunnel segmental joints and then seepage erosion is triggered, which may induce ground settlement. However, the process from fine particles erosion to the stress redistribution and soil properties’ change surrounding the tunnel and ground settlement has not been clarified up to now. For this purpose, five numerical tests of seepage erosion in granular soils around the tunnel are conducted using the Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) coupling method. The influences of buried depth and grain size distribution (GSD) of gap graded soils (mainly controlled by the fines content and mean particle size ratio from coarse to fine) on the seepage erosion around the tunnel are investigated. Eroded mass, fines loss mode, surface vertical displacement, stress redistribution, fabric anisotropy, soil behavior and water pressure around the tunnel during the seepage erosion process for five tests are presented and compared. The following results can be upscaled to the practical tunnel engineering, such as: (1) the number of fines loss, the eroded zone and the ground settlement increase with buried depth and mean particle size ratio; (2) the earth pressure near the crack significantly increases due to the stress redistribution induced by fines loss, and the stress redistributed area expands with buried depth; (3) the strength and stiffness of granular soils around the crack are significantly reduced by the seepage erosion. All results revealed that the CFD-DEM simulations provide a new sight on understanding the mechanics of tunnel seepage erosion from a microscopic perspective.

Seasonal variations in amplitudes and resonance frequencies of the HVSR amplification peaks linked to groundwater

SUMMARYFollowing the installation of a temporary seismological network in western Greece north of the Gulf of Patras, we determined the quality of the sites of each of the 10 stations in the network. For this, we used the horizontal-to-vertical spectral ratio (HVSR) method and calculated an average curve over randomly selected days between 0 and 10 Hz. The daily HVSR curve is determined by the HVSR 12-hr calculation (1 hr every two) without distinction between seismic ambient noise and earthquake signal. The HVSR curves obtained can be classified in three categories: flat curves without amplification, curves with a amplification peaks covering a large frequency range, and curves with one or more narrow peaks. In this third category C3, one station has one peak, two have two and one has three. On the contrary of what it is commonly assumed, the amplitudes and the resonance frequencies of these narrow peaks are not stable over time in C3. We determined the maximum of the amplitude of each peak with the corresponding central frequency for each day during 2.5 yr. Except for the station with three peaks, which finally appears stable within the uncertainties, the principal peak exhibits a seasonal variation, with a maximum in winter and a minimum in summer, the observations being more dispersed during winter. The second peak, when it exists, varies in the same way except at one station where it varies oppositely. These variations are clearly correlated with the loading and unloading cycle of the underlying aquifers as shown by the comparison with water level and yield measurements from wells located close to the stations. Moreover, they are also correlated with the vertical surface displacements observed at continuously recording GPS stations. The dispersion of the observed maximum amplitude in winter is probably related to the rainfall and the soil moisture modifying the S-wave velocity as revealed by other studies. From this study, we would like to emphasize that the use the HVSR method to constrain the S-wave velocity and the thickness of the sediment layer over the bedrock in the basin, has to be done with caution. Upon further confirmation of its robustness, the HVSR methodology presented here could be a good and easy-to-use tool for a qualitative survey of the aquifer backdrop and its seasonal behaviour, and of the soil moisture conditions.

Vertical surface displacement of mainland China from GPS using the multisurface function method

The annual periodic deformation of Earth’s surface can be obtained indirectly using existing models. However, model reliability is affected by numerous uncertain factors such as indirect observation, inversion algorithms, and other factors. In this study, a model of annual vertical surface displacements of mainland China is built based on the direct observation of deformation by 234 continuous Global Positioning System (GPS) stations and unified data processing using the multisurface function method (referred to as the GPS model). The GPS model shows that the weighted root mean square (WRMS) is reduced for 97% of the GPS stations after applying the model correction. The average, maximum, and minimum reductions in the WRMS are 11.6%, 37.2%, and −3.6%, respectively. The slope of the fit lines are 0.40 and 0.61 for the GPS/SLM and GPS/GRACE annual periodic amplitudes, respectively, while a slope of 0.79 for GPS/GPS model from this paper, showing the advantage of GPS model in the representing of surface displacement. Additionally, the GPS model can accurately reflect the detailed motion characteristics of mainland China, particularly in areas between large and small hydrological changes. The difference between models and GPS observation in mainland China may be related to the leakage errors in the GRACE data processing and large uncertainty in the land water storage in SLM, indicating that GPS model may provide more realistic load estimates in mainland China. The GPS model can accurately describe the annual signal, which will be extremely important for practical applications and geoscience research in the future.

RSE-based flooding prediction within territories of closed coal mines of Ukraine

The article highlights the aspects of RSE technologies adaptation during the forward hydrogeological predictions development and for the purposes of the surface flooding zones spreading estimation within coal-mines fields, being flooded. Previously developed numerical geofiltration model allows to return filtration settings of the massif of rocks, that was broken due to coal extraction, and to identify the influence features of the mine workings flooding regime on the general hydrodynamic settings around the flooded mines. As a result of geofiltration modeling the forecast cartographic scheme of groundwater table level position at the final stage of mine workings flooding was obtained. To take into account the influence of surface subsidence over the mine workings on flooding zones distribution, the values of maximum possible vertical surface displacements over the mine workings contours were calculated, based on geological and surveying data. The relief mathematical model was developed with given expected vertical deformations using the GIS-techniques and the original DEM of the territory.The result of the radar satellites images processing is a cartographic model that demonstrates the intensity of uplift movements of the earth surface. Areas of distribution of large-amplitude movements (10-20 mm/year) were determines. As a result, an updated scheme of the forecasted flooded zones was developed.

Assimilation of Ground‐Based GPS Observations of Vertical Displacement into a Land Surface Model to Improve Terrestrial Water Storage Estimates

AbstractGround‐based Global Positioning System (GPS) observations of vertical surface displacement can be used to study terrestrial water storage (TWS) change after properly accounting for nonhydrological loading effects. This study systematically merged ground‐based GPS observations of vertical displacement into a land surface model in order to better estimate TWS. Assimilation was conducted across two snow‐dominated watersheds in the western United States using a one‐dimensional ensemble Kalman filter (EnkF). Modeled estimates were compared against TWS retrievals derived from the Gravity Recovery and Climate Experiment (GRACE) mission and in situ measurements of snow water equivalent (SWE), soil moisture, and runoff. The GPS data assimilation (GPS DA) technique improves prediction skill of TWS anomalies relative to the Open Loop (OL; model run without assimilation) when compared against GRACE TWS retrievals, especially during an extended drought period post‐2011 (e.g., correlation coefficient ROL = 0.46 and RGPSDA = 0.82 in the Great Basin). Furthermore, GPS DA improves SWE estimation with improved R values found over 76% and 69% of all pixels collocated with in situ stations in the Great Basin and Upper Colorado watersheds, respectively. GPS DA estimates of surface soil moisture and runoff, however, exhibit degraded performance relative to the OL due to the limited sensitivity of GPS observations to surface soil moisture variations and the lack of a dynamic surface routing scheme as well as other missing model physics (e.g., river and dam regulation, irrigation‐related water withdrawals, surface water impoundments) that are not included in the Catchment Land Surface Model.

New Insights Into the Slip Budget at Nankai: An Iterative Approach to Estimate Coseismic Slip and Afterslip

AbstractThe slip budget at a subduction zone megathrust is met by a spectrum of slip behaviors including coseismic slip from great earthquakes, afterslip, episodic tremor and slip (ETS), long‐term slow slip events (SSEs), and quasisteady interseismic creep. Long‐term geodetic monitoring at the Nankai subduction zone in southwest Japan has recorded deformation observations spanning nearly a complete earthquake cycle, making this region the best study area for obtaining a full understanding of how the slip budget is partitioned along the interface and how the rheological conditions evolve through space and time. In this work, we conduct an iterative inversion of vertical surface displacement data to jointly estimate coseismic slip during the 1944/46 Tonankai and Nankai earthquakes, spatiotemporal afterslip history following those earthquakes, and postseismic mantle flow. A suite of postseismic models with variable elastic slab and plate geometry and mantle viscosity all show at least 30 years of sustained afterslip within the ETS zone and the gap between the top of the ETS zone and the fully coupled zone. This result demonstrates that stable, long‐duration afterslip is possible in the ETS zone. Summing the estimated cumulative slip from this study with estimates from previous studies of cumulative slip during the interseismic period, including episodic SSEs, we find that eastern Shikoku island has nearly met all of its slip budget for a 150‐year interseismic cycle, whereas western Shikoku island has a slip deficit of nearly half the budget (4 out of 8.25 meters) above 20 km depth on the subduction interface.

KINEMATIC MODEL OF THE SLOW-MOVING KOSTANJEK LANDSLIDE IN ZAGREB, CROATIA

The interpretation of landslide kinematics provides important information for those responsible for the management of landslide risk. This paper presents an interpretation of the kinematics of the slow-moving Kostanjek landslide, located in the urbanized area of the city of Zagreb, Croatia. The sliding material (very weak to weak marls, often covered with clayey topsoil) exhibits plastic, rather than rigid behavior. Due to this reason, and low landslide velocities, landslide features, such as main scarps or lateral flanks, are barely noticeable or do not exist in most of the landslide area. The data used for the kinematic interpretation were obtained from 15 GNSS sensors, for the period of 2013-2019. The monitoring data revealed a different spatial and temporal distribution of landslide velocities, resulting as a consequence of geomorphological conditions and forces that govern the landslide movements. Temporally, eight periods of faster movements and seven periods of slower movements were determined. Spatially, velocities measured in the central part of the landslide were higher than on its boundaries. The interpretation of the surface (horizontal and vertical) displacements and the direction of movement reveal a new insight into the engineering geological model and provide important information for the management of the Kostanjek landslide risk.

Land Surface Subsidence Due to Mining-Induced Tremors in the Upper Silesian Coal Basin (Poland)—Case Study

Seismic phenomena threaten land-based buildings, structures, and infrastructure and can transform land topography. There are two basic types of seismic phenomena, namely, tectonic and anthropogenic, which differ mainly in epicenter depth, surface impact range, and magnitude (energy). This article shows how a land surface was changed by a series of seven rock mass tremors of magnitude ML = 2.3–2.6 in March–May 2017. Their immediate cause was the “momentary” acceleration of void clamping, which was activated by local and short-term seismic phenomena caused by human activity. The induced seismic events resulted from the geological structure of the rock mass, which in the specific region of examination was classified as being highly prone to mining tremors. The authors focused on describing vertical surface displacements in the Upper Silesian Coal Basin in the south of Poland. The surface deformations were identified using DInSAR technology, which allows quasi-continuous monitoring of large areas of land surface. The present research used freely available data from the Copernicus Program and seismic data from the European Plate Observing System.

The Relationship between Surface Displacement and Groundwater Level Change and Its Hydrogeological Implications in an Alluvial Fan: Case Study of the Choshui River, Taiwan

Balancing the demand of groundwater resources and the mitigation of land subsidence is particularly important, yet challenging, in populated alluvial fan areas. In this study, we combine multiple monitoring data derived from Multi-Temporal InSAR (MTI), GNSS (Global Navigation Satellite System), precise leveling, groundwater level, and compaction monitoring wells, in order to analyze the relationship between surface displacement and groundwater level change within the alluvial fan of the Choshui River in Taiwan. Our combined time-series analyses suggest, in a yearly time scale, that groundwater level increases with the vertical surface displacement when the effect of pore water pressure dominates. Conversely, this relationship is negative when the effect of water-mass loading predominates over pore water pressure. However, the correlation between the vertical surface displacement and the groundwater level change is consistently positive over the time scale of two decades. It is interpreted that the alluvial fan sequence in the subsurface is not fully elastic, and compaction is greater than rebound in this process. These findings were not well reported and discussed by previous studies because of insufficient monitoring data and analyses. Understanding the combined effect of groundwater level change and vertical surface displacement is very helpful for management of land subsidence and usage of groundwater resources. The spatial and temporal integration of multi-sensors can be applied to overcome the limitations associated with the single technique and provides further insights into land surface changes, particularly in highly populated alluvial fan areas.

Polarization manipulation of surface acoustic waves by metallization patterns on a piezoelectric substrate

Surface acoustic waves (SAWs) with large normal (vertical) surface displacement at the surface are commonly utilized in microfluidic actuators in order to provide the desired momentum transfer to the fluid. We present an alternative concept using a SAW with comparatively small vertical displacement. Such a SAW passes underneath the microfluidic vessel walls with minimum losses but it needs to be converted inside the vessel into surface vibrations with large vertical displacements. The principal operability of the above idea is illustrated by experimental and numerical studies of the polarization conversion of a leaky SAW on 64° rotated Y-cut of lithium niobate owing to the partial metallization of the substrate surface. In particular, it is found that vertical displacements on the metallized surface can be up to 3.5 times higher as compared to their values on the free surface. Results of computations agree reasonably well with measurements carried out with a laser Doppler vibrometer and allow the clarification of some specific features of this polarization conversion by means of spatial frequency analysis.

Effect of antenna snow intrusion on vertical GPS position time series in Antarctica

Vertical surface displacements from continuous Global Positioning System (GPS) stations often show strong seasonal signals, which in some cases may be associated with surface mass loading, including hydrological, and non-tidal oceanic and atmospheric loading. In Antarctica, many GPS stations show vertical motions in phase with seasonal snow accumulation changes, but these variations cannot be fully explained with snow load variations between seasons. Instead we show, for many sites in Antarctica, that a significant component of the annual cycle in vertical GPS coordinates time series may be related to snow/ice inside antennas causing as an artefact apparent seasonal variation, with amplitudes of up to 4 mm. We present a method based on the Empirical Mode Decomposition (EMD) algorithm to remove this artefact signal. The corrected GPS time series show an improvement in the agreement with displacements predicted by elastic modelling using GRACE-derived surface mass loads.

Fine-scale spatiotemporal variation in subsidence across California’s San Joaquin Valley explained by groundwater demand

Achieving sustainable agricultural groundwater use remains a significant challenge worldwide in part because data on groundwater withdrawals are limited. A new generation of interferometric synthetic aperture radar (InSAR) data provide high spatial- and temporal- resolution measurements of subsidence and uplift of the earth’s surface, which are known to reflect change in groundwater storage below. Here, we establish for the first time a quantitative link between local irrigation water demand and InSAR-derived vertical land surface displacements in California’s San Joaquin Valley, with the goal of increasing the utility of remotely sensed displacements for understanding and managing groundwater at fine scales. We relate 100 m, sub-monthly displacements to estimates of irrigation water demand generated from land cover and weather data by performing a suite of physical process-motivated statistical analyses that leverage (i) temporal variations in surface water supplies created by climate, and (ii) spatial variations in water demand created by different land uses. Between 2015 and 2017, cultivated land experienced up to seven times the total subsidence, and up to nine times the dry year subsidence rate, of uncultivated land. In uncultivated areas, subsidence rates differed minimally across dry and wet years. In contrast, within cultivated areas, dry year subsidence rates were more than double wet year rates, indicating increased agricultural groundwater pumping under diminished precipitation and surface water supplies. Mean subsidence, and the marginal response of subsidence to water demand, were greatest for cultivated lands and for field and pasture crops in particular, and were also proportional to distance from surface water supply infrastructure. These findings demonstrate that land surface observations have the potential for use in the quantification of connected surface water and groundwater processes at policy-relevant scales.

Static stiffness of rigid foundation resting on elastic half-space using a Galerkin boundary element method

In this work, a simple and effective numerical model is proposed for studying flexible and rigid foundations in bilateral and frictionless contact with a three-dimensional elastic half-space. For this purpose, a Galerkin Boundary Element Method for the substrate is introduced, and both surface vertical displacements and half-space tractions are discretized by means of a piecewise constant function. The work focuses on a transversely isotropic substrate having the plane of isotropy parallel to the half-space boundary, hence the relationship between vertical displacements and half-space reactions is given by Michell solution, reducing to Boussinesq solution for an isotropic half-space. Several numerical tests are performed for showing the effectiveness of the model, on one hand by determining vertical displacements of flexible rectangular foundations subjected to vertical pressures, on the other hand by accurately determining the translational and rotational stiffness of rigid rectangular and L-shaped foundations. Particular attention is given to the determination of the center of stiffness in case of unsymmetrical foundations, since it turns out to be not coincident with foundation area centroid.