Surface deformation in California's Central Valley (CV) has long been linked to changes in groundwater storage. Recent advances in remote sensing have enabled the mapping of CV deformation and ...associated changes in groundwater resources at increasingly higher spatiotemporal resolution. Here, we use interferometric synthetic aperture radar (InSAR) from the Sentinel‐1 missions, augmented by continuous Global Positioning System (cGPS) positioning, to characterize the surface deformation of the San Joaquin Valley (SJV, southern two‐thirds of the CV) for consecutive dry (2016) and wet (2017) water years. We separate trends and seasonal oscillations in deformation time series and interpret them in the context of surface and groundwater hydrology. We find that subsidence rates in 2016 (mean −42.0 mm/yr; peak −345 mm/yr) are twice that in 2017 (mean −20.4 mm/yr; peak −177 mm/yr), consistent with increased groundwater pumping in 2016 to offset the loss of surface‐water deliveries. Locations of greatest subsidence migrated outwards from the valley axis in the wetter 2017 water year, possibly reflecting a surplus of surface‐water supplies in the lowest portions of the SJV. Patterns in the amplitude of seasonal deformation and the timing of peak seasonal uplift reveal entry points and potential pathways for groundwater recharge into the SJV and subsequent groundwater flow within the aquifer. This study provides novel insight into the SJV aquifer system that can be used to constrain groundwater flow and subsidence models, which has relevance to groundwater management in the context of California's 2014 Sustainable Groundwater Management Act (SGMA).
Key Points
The timing, magnitude, and spatial pattern of deformation in the San Joaquin Valley changes between dry and wet water years
Seasonal amplitudes and peak seasonal uplift timing of deformation indicate possible recharge locations and pathways for groundwater flow
Geodetic observations have the potential to provide insight into aquifer dynamics at policy relevant scales
The driving force for transient vertical motions of Earth's surface remains an outstanding question. A main difficulty lies in the uncertain role of the underlying mantle, especially during the ...geological past. Here I review previous studies on both observational constraints and physical mechanisms of North American topographic evolution since the Mesozoic. I first summarize the North American vertical motion history using proxies from structural geology, geochronology, sedimentary stratigraphy, and geomorphology, based on which I then discuss the published physical models. Overall, there is a progressive consensus on the contribution of mantle dynamic topography due to buoyancy structures associated with the past subduction. At the continental scale, a largely west‐to‐east migrating deformation pattern suggests an eastward translation of mantle dynamic effects, consistent with models involving an eastward subduction and sinking of former Farallon slabs since the Cretaceous. Among the existing models, the inverse model based on an adjoint algorithm and time‐dependent data constraints provides the most extensive explanations for the temporal changes of North American topography since the Mesozoic. At regional scales, debates still exist on the predicted surface subsidence and uplift within both the western and eastern United States, where discrepancies are likely due to differences in model setup (e.g., mantle dynamic properties and boundary conditions) and the amount of time‐dependent observational constraints. Toward the development of the next‐generation predictive geodynamic models, new research directions may include (1) development of enhanced data assimilation capabilities, (2) exploration of multiscale and multiphysics processes, and (3) cross‐disciplinary code coupling.
Key Points
North America experienced a west‐to‐east migrating long‐wavelength dynamic subsidence since 100 Ma
The main control on this dynamic topography is subduction of the Farallon plate since the Mesozoic
Predictive models with data assimilation are promising in deciphering continental evolution
SUMMARY
Constitutive theory for viscoelasticity has broad application to solid mantle or ice deformations driven by tides, surface mass variations, and post-seismic flow. Geophysical models using ...higher order viscoelasticity can better accommodate geodetic observations than lower-order theory, typically provided by tensor versions of Maxwell, 4-parameter Burgers or standard linear (Zener) rheology. We derive, for the first time, a mathematical description of a compressible version of the extended Burgers material (EBM) model paradigm which has a distribution function of relaxation spectra. The latter model is often used for parametrizing high temperature background transient responses in the rock physics and mechanics laboratory setting and have demonstrated application to low frequency seismic wave attenuation. A new generalization of this practical anelastic model is presented and applied to the glacial isostatic adjustment momentum equations, thus providing useful guidance for generating initial-value boundary problem-solving software for quite general coding strategies. The solutions for the vertical motion response to a suddenly imposed surface load reveal a short-term transience of substantial amplitude.
Volcanic crises are often associated with magmatic intrusions or the pressurization of magma chambers of various shapes. These volumetric sources deform the country rocks, changing their density, and ...cause surface uplift. Both the net mass of intruding magmatic fluids and these deformation effects contribute to surface gravity changes. Thus, to estimate the intrusion mass from gravity changes, the deformation effects must be accounted for. We develop analytical solutions and computer codes for the gravity changes caused by triaxial sources of expansion. This establishes coupled solutions for joint inversions of deformation and gravity changes. Such inversions can constrain both the intrusion mass and the deformation source parameters more accurately.
Plain Language Summary
Volcanic crises are usually associated with magmatic fluids that intrude and deform the host rocks before potentially breaching the Earth's surface. It is important to estimate how much fluid (mass and volume) is on the move. Volume can be determined from the measured surface uplift. Mass can be determined from surface gravity changes. The fluid intrusion increases the mass below the volcano, thereby increasing the gravity and pressurizing the rocks. This dilates parts of the host rock and compresses other parts, changing the rock density and redistributing the rock mass. This causes secondary gravity changes, called deformation‐induced gravity changes. The measured gravity change is always the sum of the mass and deformation‐induced contributions. Here, we develop mathematical equations for the rapid estimation of these deformation‐induced gravity changes caused by arbitrary intrusion shapes. This way we can take the mass contribution apart from the deformation contribution. We show that by using this solution not only the intrusion mass, but also other intrusion parameters, including the volume, depth, and shape can be calculated more accurately.
Key Points
We develop analytical solutions for gravity changes due to the point Compound Dislocation Model simulating triaxial expansions
Rapid coupled inversions of deformation and gravity changes, accounting for deformation‐induced gravity changes are now possible
For shallow sources, estimation errors in the chamber volume change may lead to large biases in the simulated gravity changes
Globally uniform (i.e., eustatic) sea-level trends with time scales approaching 100 Myr have been inferred from both seismic and backstripping stratigraphic analysis at a small set of geographic ...sites that are presumed to lie on stable continental platforms and passive continental margins characterized by simple thermal subsidence histories (e.g., the New Jersey margin, the western African margin). We demonstrate, using mantle flow simulations based on high resolution seismic tomography, that both the New Jersey margin and the conjugate western African margin have been subject to orders of 100 m of dynamic (i.e., flow induced) topography change over the last 30 Myr. We also show that the changing pattern of downwelling mantle flow associated with plate subduction is a significant contributor to the background eustatic sea-level trend, which is also of order 100 m during the 30 Myr time window. Therefore, Late-Cenozoic variations of dynamic topography on these passive margin sites are comparable to the eustatic sea-level changes and can partially mask the latter. Furthermore, even if the observed trend could be accurately corrected for local dynamic topography variation, the residual eustatic signal does not merely reflect changes in mean spreading rates at mid-ocean ridges. We conclude that the observed long term sea-level variations at so-called “stable” sites cannot be interpreted as eustatic. Moreover, previous analyses that have used long-term sea-level trends as a proxy for spreading rates and geochemical fluxes must be revisited.
Analysis of high-resolution seismic profiles integrated with archaeological data along the coast has allowed quantifying the last ∼10 ka BP displacements in the offshore part of the Campi Flegrei ...resurgent caldera, one of the world's highest-risk volcanic areas. Previous onland studies revealed that, following the Neapolitan Yellow Tuff (NYT) eruption at 15 ka, post-caldera evolution was associated with rapid ground uplift and subsidence cycles. In this paper, we use the stacking pattern of Prograding Wedges (PWs) and Aggrading Fills (AF) to reconstruct relative sea-level changes and estimate the amount of vertical deformation in the Pozzuoli Bay, the submerged part of the caldera. We document five generations of prograding wedges (PW1 to PW5), associated with as many periods of relative ground stability between uplift and subsidence. Instead, deposition of aggrading fills above prograding wedges underpins the subsidence that typically follows volcanic unrest and uplift. The older wedges PW1 and PW2 are larger and likely indicate whole-caldera uplift events. In particular, the development of PW2 starting from ∼5.2 ka is related to the rapid growth of a resurgent dome in the central part of the caldera. After ∼3.7 ka, subsidence prevailed in the caldera leading to deposition of an aggrading fill (AF2). However, subsidence was interrupted by short-term uplift episodes in historical times at (100 BCE-100 CE, 600–700 CE, 1430–1538 CE) that led to the growth of comparatively minor-sized wedges PW1 to PW3, respectively. Displacement of coastal infrastructures of the Roman age (∼2 ka BP) is consistent with the vertical motion retrieved by the seismostratigraphic analysis, and further indicates the existence of two deformation signals. A short-wavelength signal confined to the Pozzuoli Bay reflects the contribution of an intra-caldera source. This signal is superposed to a long-wavelength regional subsidence increasing between Naples and Procida Island from 1.5 to 2 mm/a, respectively. The east-to-west enhancing subsidence likely reflects the transition between the uplifting Apennines and the foundered Tyrrhenian back-arc basin.
•High-resolution seismic profiles analysis in the offshore Campi Flegrei caldera•Seismostratigraphic bodies document relative sea-level changes•Quantitative reconstruction of vertical ground displacements in the Holocene•Roman-age coastal remains constrain ground deformation in the last 2 ka.•We disentangle the contribution of intra-caldera dynamics and regional tectonics.
Geodetic GNSS observations at 43 sites well distributed over the Southern Patagonian Icefield region yield site velocities with a mean accuracy of 1 mm/a and 6 mm/a for the horizontal and vertical ...components, respectively. These velocities are analyzed to reveal the magnitudes and patterns of vertical and horizontal present-day crustal deformation as well as their primary driving processes. The observed vertical velocities confirm a rapid uplift, with rates peaking at 41 mm/a, causally related to glacial-isostatic adjustment (GIA). They yield now an unambiguous preference between two competing GIA models. Remaining discrepancies between the preferred model and our observations point toward an effective upper mantle viscosity even lower than 1.6⋅1018 Pas and effects of lateral rheological heterogeneities. An analysis of the horizontal strain and strain-rate fields reveals some complex superposition, with compression dominating in the west and extension in the east. This deformation field suggests significant contributions from three processes: GIA, a western interseismic tectonic deformation field related to plate subduction, and an extensional strain-rate field related to active Patagonian slab window tectonics.
•Crustal deformation at the Southern Patagonian Icefield observed at 43 GNSS sites.•Glacial-isostatic adjustment generates crustal uplift of up to 4 cm per year.•Plate collision and the Patagonian slab window contribute also to horizontal strain.
In accordance with the “Liquefaction Experiments and Analysis Projects (LEAP )” guidelines, class-A, B and C predictions are performed for the response of centrifuge tests on a sloped configuration ...of Ottawa-F65 soil in a rigid container. The objective of this paper is to discuss important aspects on the calibration process of a pressure-dependent bounding surface constitutive model for the simulation of centrifuge experiments. The constitutive model used in this study is based on the theory of Critical State Soil Mechanics that has shown to be suitable to represent the behavior of cohesionless soils. Results of class-A predictions match experiment data reasonably well. An attempt is made to find a single set of material parameters to be used for class-B and class-C prediction of all six centrifuge tests.
•Details of a finite element model used for simulating centrifuge test are given.•Results of class-A, B and C prediction on centrifuge tests are presented and discussed.•Discussion on calibration of a constitutive model is given.•Finding a single set of representative material parameter to be used in simulation of different centrifuge experiments is found to be impractical.
This study aims to correct for long-term vertical land motions at tide gauges (TG) by estimating high-accurate GPS vertical velocities at co-located stations (GPS@TG), useful for long-term sea-level ...change studies and satellite altimeter drift monitoring. Global Positioning System (GPS) data reanalyses are mandatory when aiming at the highest consistency of the estimated products for the whole data period. The University of La Rochelle Consortium (ULR) has carried out several GPS data reanalysis campaigns with an increasing tracking network, an improving processing strategy and the best methodology. The geodetic results from the latest GPS velocity field estimated at ULR (named ULR5) are presented here. The velocity field includes 326 globally distributed GPS stations, from which 200 are GPS@TG (30% more than previous studies). The new GPS data processing strategy, the terrestrial frame definition and the velocity estimation procedures are described. The quality of the estimated vertical velocities is empirically assessed through internal and external velocity comparisons, including the analysis of the time-correlated noise content of the position time series, to be better than 0.6mm/yr (2 sigma). The application of this velocity field is illustrated to appraise to what extent vertical land motions contaminate the estimates of satellite altimetry drifts. The impact on the altimeter-derived sea level trends was evaluated to be up to 0.6mm/yr. Worldwide TGs were grouped into regions in order to explore long-term spatial sea level variability in the rates of sea level change. By taking into account the vertical land motion of the tide gauges, the dispersion of the observed sea level rates within each region was reduced by 60%. Long-term regional mean sea level variations up to 70% from the global mean were found.
► A GPS velocity field near tide gauges is applied for sea level change. About 30% more TGs than previous studies are used. ► The precision of the velocities is of 0.3mm/yr and closely spaced GPS stations generally agreeing to 0.4mm/yr. ► The long-term spatial sea level variability is analysed globally. Regional variations of 70% from the global mean are found. ► The vertical land motion of tide gauges contributes to the uncertainty of the altimetry drift estimates up to 0.6mm/yr.
SUMMARY
Studies of glacial isostatic adjustment (GIA) provide important constraints on the Earth's mantle viscosity. Most GIA models assume Newtonian viscosity through the mantle, but laboratory ...experimental studies of rock deformation, observational studies of seismic anisotropy, and modelling studies of mantle dynamics show that in the upper mantle non-Newtonian viscosity may be important. This study explores the non-Newtonian effects on the GIA induced variations in mantle stress and viscosity and on surface observables including vertical displacement, relative sea level (RSL) and gravity change. The recently updated and fully benchmarked software package CitcomSVE is used for GIA simulations. We adopt the ICE-6G ice deglaciation history, VM5a lower mantle and lithospheric viscosities, and a composite rheology that combines Newtonian and non-Newtonian viscosities for the upper mantle. Our results show that: (1) The mantle stress beneath glaciated regions increases significantly during deglaciation, leading to regionally reduced upper mantle viscosity by more than an order of magnitude. Such effects can be rather localized at the periphery of glaciated regions. However, non-Newtonian effects on far-field mantle viscosity are negligibly small. GIA induced stress is also significant in the lithosphere (∼30 MPa) and lower mantle (∼2 MPa). (2) The predicted RSL changes from non-Newtonian models display distinct features in comparison with the Newtonian model, including more rapid sea level falls associated with the rapid deglaciation at ∼14 000 yr ago followed by a more gradual sea level variation for sites near the centres of formerly glaciated regions, and an additional phase of sea level falls for the last ∼8000 yr for sites at the ice margins. Similar time-dependence associated with the deglaciation is also seen for rate of vertical displacement, suggesting a relatively slow present-day rates of vertical displacement and gravity change. These features can be explained by the non-Newtonian effects associated with a loading event which manifest a fast relaxation stage followed by a relative slow relaxation stage. Our results may provide GIA diagnoses for distinguishing non-Newtonian and Newtonian rheology.
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