SUMMARY
Understanding water redistribution on Earth's surface is essential to hydrological applications and water management. Variations in water mass loads have been observed by the Gravity Recovery ...and Climate Experiment (GRACE), but the low spatial resolution of GRACE limits determination of their distribution in detail. Hydrologic models provide higher spatial resolution water mass loads, but may include larger uncertainties. In this study, we develop high-resolution surface mass loads over the Amazon basin using forward modelling by combining GRACE data and a hydrologic model. River routing discharge is also included as a priori information because of the large water volume changes on relatively narrow channels in the Amazon basin. These high-resolution surface mass loads constrained by river routing agree with GRACE observations when spatially smoothed. Vertical deformation estimated from these high-resolution loads agree with Global Navigation Satellite System (GNSS) observations, at both seasonal and inter-annual timescales. In particular the most improved agreement is obtained at the NAUS GNSS station, close to the main channel of the Amazon, relative to predictions made using GRACE data. At two other stations (APSA and MAPA) near the main channel, the estimated vertical deformations apparently differ from observation, but much of the discrepancy is reduced when river path is corrected in river-routing model, indicating the importance of water loads on river channel to understand crustal displacement in the area.
Quaternary paleoshorelines are common landforms on the island of Crete, a forearc high above the Hellenic Subduction Zone. These geomorphic markers are useful on Crete and elsewhere in determining ...coastal uplift rates, the identification of active geologic structures, and to constrain geodynamic models and seismic hazards. Controversy exists in the literature regarding the formation mechanisms and age of late Pleistocene paleoshorelines on Crete that has led to competing models of the uplift history, tectonic evolution, and seismic hazards of the Hellenic forearc. We present new mapping and results from luminescence and radiocarbon geochronology of paleoshoreline deposits that constrain the spatial and temporal pattern of rock uplift around the Cretan coastline. Existing and new radiocarbon data are variable and show no obvious age-elevation trends within individual terrace sequences. By contrast, nearly all luminescence ages, some from shorelines dated with radiocarbon, show positive age-elevation trends and range from 60–220 ka suggesting that all dated paleoshorelines are beyond the limits of radiocarbon. We propose that the inconsistencies between the different geochronological methods are the result of secondary contamination of young carbonate, possibly from meteoric waters, that bias radiocarbon in Cretan Pleistocene marine fossils. Most luminescence ages closely correlate with the timing of mid-to-late Pleistocene relative sea level highstands, consistent with stratigraphic observations. Calculated coastal uplift rates using a Monte-Carlo error analysis range from ∼0–1.2 mm/yr; the lowest uplift rates are found along the northern and eastern coasts of the island, while the most rapid are focused along the southern and western coasts where active normal faults are observed offsetting paleoshoreline sequences. Based on this new data, we favor a tectonic model where slip along upper crustal normal faults acts to locally augment a steady regional signal of uplift along the south and west coast, interpreted to result from the deep underplating of rock at the base of the subduction wedge beneath Crete. Arcward of the contact between the upper plate Moho and the top of the subducting slab, crustal thinning will occur in the orogenic wedge resulting in subsidence along the north coast of Crete.
•New luminescence and radiocarbon geochronology from paleoshorelines on Crete, Greece.•Paleoshorelines form during eustatic sea level highstands.•We derive a coastal mid-to-late Pleistocene uplift rate map for Crete and Gavdos.•South coast uplift is partially generated by footwall uplift along extensional faults.•Footwall uplift is accompanied by a regional uplift signal likely from underplating.
Using measurements of continuous GPS stations and GRACE across the southeastern Tibetan Plateau, we found that the GRACE-derived vertical displacements are highly correlated with GPS-modeled vertical ...annual and semiannual displacements, which demonstrates that the vertical seasonal variations on ground surface are mainly caused by hydrological mass loading. After removing GRACE-modeled seasonal variations from the GPS time series, we used a stacking technique to filter out the common mode errors. Then we estimated the best noise model for the filtered time series, which can be best characterized by power law noise model. Finally, we determined the rates of vertical crustal movement of southeastern Tibetan Plateau. Our results suggest that the southeastern Tibetan Plateau is undergoing uplift, whereas the southern Sichuan–Yunnan fragment is subsiding with respect to the region to the north. The assumption of uniform extension throughout the crust does not explain the subsidence of southern Sichuan–Yunnan fragment.
•GRACE and GPS vertical seasonal variations are highly correlated in study region.•CMEs were filtered out after removing GRACE-modeled seasonal variations from GPS.•The filtered GPS time series can be best characterized by power law noise model.•The vertical crustal movement of southeastern Tibetan Plateau was obtained.
Greenland's bedrock responds to ongoing ice loss with an elastic vertical land motion (VLM) that is measured by Greenland's Global Navigation Satellite System (GNSS) Network (GNET). The measured VLM ...also contains other contributions, including the long‐term viscoelastic response of the Earth to the deglaciation of the last glacial period. Greenland's ice sheet (GrIS) produces the most significant contribution to the total VLM. The contribution of peripheral glaciers (PGs) from both Greenland (GrPGs) and Arctic Canada (CanPGs) has not carefully been accounted for in previous GNSS analyses. This is a significant concern, since GNET stations are often closer to PGs than to the ice sheet. We find that, PGs produce significant elastic rebound, especially in North and East Greenland. Across these regions, the PGs produce up to 32% of the elastic rebound. For a few stations in the North, the VLM from PGs is larger than that due to the GrIS.
Plain Language Summary
The solid Earth has long been compressed by the weight of overlying ice caps and ice sheets. As climate change causes ice to melt, and these loads diminish, the solid Earth relaxes, producing instantaneous elastic rebound and delayed viscoelastic rebound of the bedrock. Such displacements are recorded by the 58 permanent Global Navigation Satellite System (GNSS) stations that comprise the Greenland GNSS Network (GNET). So far, only the ice mass changes from the ice sheet have been considered in the analyses of deformation recorded by GNET. Here, we evaluate the contribution from the peripheral glaciers, which are often much closer to the stations than the ice sheet. We find that at many stations, the signal produced by the peripheral glaciers is non‐negligible, especially in North and East Greenland. This allows us to better understand the residual rebound signal produced by the end of the last ice age.
Key Points
Elastic rebound due to ice loss from peripheral glaciers can exceed that due to ice sheet loss
This effect is most significant at Global Navigation Satellite System Network (GNET) sites in North and East Greenland
Peripheral glacier loss should be acknowledged when isolating glacial isostatic adjustment from GNET
SUMMARY
The relationship between the Green's function and the average correlations of the elastic displacements within a diffuse field has been firmly established. The energies of horizontal and ...vertical motion in such a field are proportional to the imaginary part of the corresponding diagonal components of the Green's tensor for coincident source and receiver. Given this remarkable connection, we examine the partitions of elastic waves due to dynamic horizontal and vertical surface loads in a layered elastic media. The elastic radiation characteristics for horizontally layered media are much more complicated than for the homogeneous half-space. While the corresponding power partitions of the different types of waves in a half-space do not vary with respect to frequency, even in an elastic medium consisting of layers over a half-space, the modal structure shows strong variations in the frequency, mainly around the main peak and the minimum of the horizontal-to-vertical spectral ratio (HVSR). Using a test model with a moderately high impedance contrast, we find that most of the energy density of the horizontal displacements is concentrated in the fundamental mode of the Love waves, reaching ∼80 per cent of the power in the horizontal components. The vertical displacement of the P-SV body waves reaches a maximum of ∼85 per cent, while the fundamental mode of Rayleigh waves reaches a maximum of ∼99 per cent of the available power in the vertical motion. With this analysis, it is possible to analyse the multimodal effects in the dispersion diagrams and explicitly relate the partition of the energy density with the dispersion curves and the HVSR under the diffuse field assumption.
We performed a numerical study to understand the dynamical mechanisms of back-arc basin formation induced by slab rollback. To this end, we used two-dimensional numerical models of an integrated ...plate–mantle convection system with 410- and 660-km phase transitions. Retrograde slab migration occurs when the slab stagnates in the transition zone or when the deep section of the slab is vertical. In both cases, slab rollback occurs because the deep slab section obstructs the descending motion of the shallow slab section with an inclination. Buoyancy of the 660-km phase boundary acts as the obstructing force in the case of stagnant slab formation, and an anchoring force against the horizontal motion works similarly in the case of vertical slabs. To balance the horizontal component of the obstructing force, a suction force at the plate boundary pulls the overriding plate toward the ocean. Back-arc spreading is produced by means of slab rollback when the overriding plate with a weak area is fixed to the model boundary. The back-arc deformation becomes compressional when the overriding plate is freely movable despite trench retreat, because the wedge mantle flow viscously drags the overriding plate toward the trench. This implies that forces tending to actuate the overriding plate away from the trench are necessary to generate back-arc extension even when trench retreat is generated by slab rollback.
► We performed numerical simulations of slab rollback with back-arc basin formation. ► Obstruction of the shallow slab motion by the deep section drives the rollback. ► Stagnant slab formation and vertical slab anchoring generate the obstructing force. ► Wedge mantle flow strongly drags a movable overriding plate toward the trench. ► Mobility of the overriding plate influences back-arc deformation.
Global Navigation Satellite System (GNSS) is used in seismology to study the ground displacements as well as to monitor the ionospheric total electron content (TEC) perturbations following seismic ...events. The aim of this work is to combine these two observations in one real-time method based on the Total Variometric Approach (TVA) to include the GNSS real-time data stream in future warning systems and tsunami genesis estimation observing both, ground motion and TEC. Our TVA couples together the Variometric Approach for Displacement Analysis Stand-alone Engine (VADASE) with the Variometric Approach for Real-Time Ionosphere Observation (VARION) algorithms. We apply the TVA to the Mw 8.3 Illapel earthquake, that occurred in Chile on September 16, 2015, and we demonstrate the coherence of the earthquake ground shaking and the TEC perturbation by using the same GNSS data stream in a real-time scenario. Nominally, we also highlight a stronger kinetic energy released in the north of the epicenter and visible in both, the ground motion and the TEC perturbation detect at 30 s and around 9.5 min after the rupture respectively. The high spatial resolution of ionospheric TEC measurement seems to match with the extent of the seismic source. The GNSS data stream by TVA of both the ground and ionospheric measurement opens today new perspectives to real-time warning systems for tsunami genesis estimation.
The E–W trending Atlas System of Maghreb consists of weakly shortened, intra-continental fold belts associated with plateau areas (“Mesetas”), extending between the south-westernmost branch of the ...Mediterranean Alpine Belt (Rif-Tell) and the Sahara Platform. Although the Atlas system has been erected contemporaneously from Morocco to Algeria and Tunisia during the Middle Eocene to Recent, it displays a conspicuous longitudinal asymmetry, with i) Paleozoic outcrops restricted to its western part; ii) highest elevation occurring in the west, both in the Atlas System and its foreland (Anti-Atlas); iii) low elevation corridors (e.g. Hodna) and depressed foreland (Tunisian Chotts and Sahel area) in the east. We analyse the origin of these striking contrasts in relation with i) the Variscan heritage; ii) crustal vertical movements during the Mesozoic; iii) crustal shortening during the Cenozoic and finally, iv) the occurrence of a Miocene–Quaternary hot mantle anomaly in the west. The Maghreb lithosphere was affected by the Variscan orogeny, and thus thickened only in its western part. During the Late Permian–Triassic, a paleo-high formed in the west between the Central Atlantic and Alpine Tethys rift systems, giving birth to the emergent/poorly subsident West Moroccan Arch. During the late Middle Jurassic–Early Cretaceous, Morocco and western Algeria were dominantly emergent whereas rifting lasted on in eastern Algeria and Tunisia. We ascribe the uplift of the western regions to thermal doming, consistent with the Late Jurassic and Barremian gabbroic magmatism observed there. After the widespread transgression of the high stand Cenomanian–Turonian seas, the inversion of the Atlas System began during the Senonian as a consequence of the Africa–Eurasia convergence. Erosion affected three ENE-trending uplifted areas of NW Africa, which we consider as lithospheric anticlines related to the incipient Africa–Europe convergence. In contrast, in eastern Algeria and Tunisia a NW-trending rift system developed contemporaneously (Sirt rifting), normal to the general trend of the Atlas System. The general inversion and orogenesis of the Atlas System occurred during two distinct episodes, Middle–Late Eocene–Oligocene and Late Miocene–Pliocene, respectively, whereas during the intervening period, the Africa–Europe convergence was mainly accommodated in the Rif-Tell system. Inversion tectonics and crustal thickening may account for the moderate uplift of the eastern Atlas System, not for the high elevation of the western mountain ranges (Middle Atlas, High Atlas, Anti-Atlas). In line with previous authors, we ascribe part of the recent uplift of the latter regions to the occurrence of a NE-trending, high-temperature mantle anomaly, here labelled the Moroccan Hot Line (MHL), which is also marked by a strip of late Miocene–Quaternary alkaline magmatism and significant seismicity.
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.
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