Consolidated Sediments Research Articles

Processes Influencing Autocompaction Modulate Coastal Wetland Surface Elevation Adjustment With Sea-Level Rise

The fate of coastal wetlands and their ecosystem services is dependent upon maintaining substrate elevations within a tidal frame that is influenced by sea-level rise. Development and application of morphodynamic models has been limited as few empirical studies have measured the contribution of key processes to surface elevation change, including mineral and organic matter addition, autocompaction of accumulating sediments and deep subsidence. Accordingly, many models presume that substrates are in equilibrium with relative sea-level rise (RSLR) and the composition of substrates are relatively homogenous. A 20-year record of surface elevation change and vertical accretion from a large tidal embayment in Australia coupled with analyses of inundation frequency and the character of sediments that have accumulated above mean sea level was analyzed to investigate processes influencing surface elevation adjustment. This study confirms the varying contribution of addition, decomposition and compression of organic material, and mineral sediment consolidation. Autocompaction of substrates was proportional to the overburden of accumulating sediments. These processes operate concurrently and are influenced by sediment supply and deposition. Vertical accretion was linearly related to accommodation space. Surface elevation change was related to vertical accretion and substrate organic matter, indicated by carbon storage above mean sea level. Surface elevation change also conformed to models that initially increase and then decrease as accommodation space diminishes. Rates of surface elevation change were largely found to be in equilibrium with sea-level rise measured at the nearest tide gauge, which was estimated at 3.5 mm y–1 over the period of measurements. As creation of new accommodation space with sea-level rise is contrary to the longer-term history of relative sea-level stability in Australia since the mid-Holocene, striking stratigraphic variation arises with deeper sediments dominated by mineral sands and surficial sediments increasingly fine grained and having higher carbon storage. As the sediment character of substrates was found to influence rates of surface elevation gain, we caution against the unqualified use of models derived from the northern hemisphere where substrates have continuously adjusted to sea-level rise and sediment character is likely to be more homogenous.

Grey Box Modelling of Decanter Centrifuges by Coupling a Numerical Process Model with a Neural Network

Continuously operating decanter centrifuges are often applied for solid-liquid separation in the chemical and mining industries. Simulation tools can assist in the configuration and optimisation of separation processes by, e.g., controlling the quality characteristics of the product. Increasing computation power has led to a renewed interest in hybrid models (subsequently named grey box model), which combine parametric and non-paramteric models. In this article, a grey box model for the simulation of the mechanical dewatering of a finely dispersed product in decanter centrifuges is discussed. Here, the grey box model consists of a mechanistic model (as white box model) presented in a previous research article and a neural network (as black box model). Experimentally determined data is used to train the neural network in the area of application. The mechanistic approach considers the settling behaviour, the sediment consolidation, and the sediment transport. In conclusion, the settings of the neural network and the results of the grey box model and white box model are compared and discussed. Now, the overall grey box model is able to increase the accuracy of the simulation and physical effects that are not modelled yet are integrated by training of a neural network using experimental data.

Assessment of Consolidation-Induced Contaminant Transport for In Situ Capping of Subaqueous Contaminated Sediments

This paper presents an investigation of the effect of sediment consolidation on contaminant transport through a sediment-cap system for in situ cappings of subaqueous contaminated sediments. Numerical simulations were conducted using the model CST3 and consider coupled consolidation and contaminant transport for representative layer geometry, material properties, and applied stress conditions. Simulation results indicate that sediment consolidation can have significant effects on contaminant breakthrough time, mass flux, cumulative mass outflow, and concentration distribution within the sediment-cap system. These effects manifest not only during the consolidation process but also long after consolidation has been completed. Traditional advective-dispersive transport analyses fail to consider transient advection induced by sediment consolidation and associated contaminant migration and changes in material properties that can lead to significantly unconservative transport results and adverse environmental impact. For example, simulation results indicate that failure to account for sediment consolidation yields a cumulative contaminant mass outflow that is underestimated by a factor greater than 6,000 within the first 3 years after cap placement and by a factor of 2 at the end of a 100-year simulation period, even though consolidation essentially is completed in the first 1.5 years.

Cephalic biomechanics underpins the evolutionary success of trilobites

AbstractArthropods (i.e. insects, spiders, crustaceans, myriapods and others), are the most successful Phanerozoic animals. The group is characterized by the possession of a segmented body, jointed limbs and a hard cuticle that is episodically moulted. One highly successful but now extinct group of arthropods is the trilobites. Trilobites underwent episodic moulting (ecdysis), and most trilobites possess facial sutures, lines of weakness in the cephalon, via which the exuviae is shed and the animal emerges. However, zones of weakness appear to represent a structural trade‐off or constraint, particularly during burrowing; sacrificing a consolidated head region useful in burrowing for the ability to moult. Here we reconcile this trade‐off by using biomechanical modelling to demonstrate that facial sutures exist in regions of low stress during the application of burrowing loads. Furthermore, facial sutures and the structure of the cephalon enable sutured trilobites to withstand greater stresses than their non‐suture counterparts. We suggest that this ability to withstand greater burrowing loads enabled trilobites to successfully invade bioturbated and more consolidated sediments of the Cambrian Sediment Revolution, thus facilitating their diversification in the Cambrian and Ordovician and contributing to the evolutionary success of this iconic arthropod group.

Simulation of the dynamic disturbance characteristics of the soft sediment in the Diexi ancient dammed lake, China

In an earlier study of the Diexi ancient dammed lake along the Minjiang River in Southwest China, 10 disturbed layers with envelope and flame structures were found in more than 240 m of lacustrine sediments. In this paper, the soft-sediment disturbances caused by earthquakes in the Diexi ancient dammed lake were studied based on field investigations and laboratory core observations. A two- to three-degree-of-freedom spring-type earthquake simulation vibration table was used to carry out disturbance tests on lacustrine sediments under different dynamic conditions. The results support the following conclusions: (1) The disturbance layers in the lacustrine sediments were caused by strong earthquakes in the region. (2) The characteristics of the disturbance layers are related to the seismic parameters and the degree of sediment consolidation. (3) The greater the earthquake intensity is, the greater the disturbance amplitude is; moreover, the lower the consolidation degree is, the greater the disturbance amplitude. (4) The simulation tests verify that the disturbance layers in the sediments of the Diexi ancient dammed lake correspond to strong earthquakes in the region. These results are valuable for ongoing palaeoseismic research in the region.

Evidence for a grounding line fan at the onset of a basal channel under the ice shelf of Support Force Glacier, Antarctica, revealed by reflection seismics

Abstract. Curvilinear channels on the surface of an ice shelf indicate the presence of large channels at the base. Modelling studies have shown that where these surface expressions intersect the grounding line, they coincide with the likely outflow of subglacial water. An understanding of the initiation and the ice–ocean evolution of the basal channels is required to understand the present behaviour and future dynamics of ice sheets and ice shelves. Here, we present focused active seismic and radar surveys of a basal channel, ∼950 m wide and ∼200 m high, and its upstream continuation beneath Support Force Glacier, which feeds into the Filchner Ice Shelf, West Antarctica. Immediately seaward from the grounding line, below the basal channel, the seismic profiles show an ∼6.75 km long, 3.2 km wide and 200 m thick sedimentary sequence with chaotic to weakly stratified reflections we interpret as a grounding line fan deposited by a subglacial drainage channel directly upstream of the basal channel. Further downstream the seabed has a different character; it consists of harder, stratified consolidated sediments, deposited under different glaciological circumstances, or possibly bedrock. In contrast to the standard perception of a rapid change in ice shelf thickness just downstream of the grounding line, we find a flat topography of the ice shelf base with an almost constant ice thickness gradient along-flow, indicating only little basal melting, but an initial widening of the basal channel, which we ascribe to melting along its flanks. Our findings provide a detailed view of a more complex interaction between the ocean and subglacial hydrology to form basal channels in ice shelves.

Monitoring and analysis of land subsidence in modern Yellow River Delta using SBAS-InSAR Technology

Modern Yellow River Delta has become one of the areas with serious land subsidence disaster in the plain area of Shandong Province. In this paper, Small Baseline Subsets - Interferometry Synthetic Aperture Radar (SBAS-InSAR) technology was used to process the Sentinel-1A data from August 2018 to October 2019 in the modern Yellow River Delta, in order to obtain the range and rate of land subsidence in the study area. At the same time, use the Leveling results of the same period to verify the accuracy. By selecting four larger land subsidence rate as feature points to analyze the characteristics of surface time series deformation, the influencing factors of land subsidence in this area are found out. The results show that during the past 2018-2019 years, the land subsidence in the the Yellow River Delta area was mainly distributed in Xianhe Town, southern the Huanghekou Town, Hubin Town, Guangrao County and its surrounding areas, DaWang Town, Yingli Town, Yangkou Town and the western part of Binhai Township, the most serious subsidence area is located in Xianhe Town, with an annual settlement rate of -204.7 mm/a. The land subsidence in the Yellow River Delta is mainly affected by groundwater overdraft, and the distribution characteristics of land subsidence funnel and deep groundwater depression funnel are basically consistent. In addition, natural factors such as consolidation of Quaternary loose sediments and regional tectonic movement also exacerbate the occurrence of land subsidence.

PREDICTION OF CONSOLIDATED COHESIVE BOTTOM EROSION BY WAVE ACTION

A consolidated cohesive sediment layer exists below a layer of sand on some beaches along the Great Lakes (glacial till) and the Gulf of Mexico. The erosion process of consolidated cohesive sediment may be gradual but irreversible (no recovery) apart from sand and gravel released from the eroded consolidated cohesive sediment. The cohesive sediment erosion rate is increased by a thin mobile layer of sand and decreased by a thick sand layer. The complicated interactions of waves, sand and cohesive bottom are simplified and incorporated into an existing cross-shore numerical model.

The nearest prospect of iodine production in Ukraine

Ukraine ranks the last place in Europe in iodized salt consumption per head of population, and mandatory salt iodization level has not yet been legalized. Iodine deficiency causes growth inhibition and memory impairment in children, efficiency decrease and endocrine system diseases – in adults. Iodized salt has not been widely used in Ukraine and the increase in the laminaria prices has been constraining its consumption. Since 1972 iodine reserves of Ukraine are recorded to be found in the waters of Severo-Sivaskoye field in Azov Sea, but due to high cost of drilling the offshore wells, iodine had not been extracted from the reservoir. The growing demand of Ukraine for iodine is met by its import from the producing countries. The rate of consolidated sediments accumulation in Krukenitsk depression of the Sarmatian basin reached 1 cm/year, and its current thickness is 6 (!) km. Formation waters from wells overfilled from flow rates up to 300 m3/d. The layers of oligomictic and polymictic sandstones with carbonaceous cement thickness up to 5 m, porosity up to 26 %, permeability –10 mD and carbonate content level up to 20 % serve as reservoirs of formation waters in Sarmatian molasses. There are no records of regularities in change of iodine content in waters of Krukenitsk depression; iodine concentration in Chop-Mukachevo depression increases to the southwest from the axis of the Vihorlat-Gutin Area. Iodinated waters contain dissolved hydrocarbon gas in small volumes with a methane content of up to 92 %. The iodine resources estimated within the studied areas of 15 km2 at Krukenitsky depression and 10 km2 at Chop-Mukachevo depression, allow its profitable commercial production for more than 50 years. Waste formation waters will be disposed through available highly permeable aquifers. In order to perform iodine production feasibility evaluation, further formation water study and detailed iodine compounds analyses are needed.

Impacts of soft soil compaction and groundwater extraction on subsidence in the Yellow River Delta

Recently, many of the world’s major river deltas have been sinking, making them increasingly vulnerable to floods and storm surges, salinization and permanent inundation. For the Yellow River delta, annual subsidence rates of several to dozens of centimeters have been reported in the past few years. The extraction of a considerable amount of groundwater due to continuous pumping is suggested as the main driver of the groundwater depression cone. Despite its scale and severity, methods to quantify subsidence are scarce. We introduce a soil mechanics approach to quantify subsidence due to the compaction of soft soil. The largest reduction in soft soil thickness, which is more than 2.6 m, occurred in the salt field area to the north of the Yellow River. Furthermore, by estimating the primary consolidation of soft soil, the subsidence caused by groundwater exploitation is quantified. In the coastal area of the delta, due to excessive exploitation of shallow underground brine resources, the maximum accumulated subsidence is as high as 2 m. Since the natural consolidation of these deltaic sediments has ended, if the current groundwater exploitation intensity is maintained, major subsidence disasters, such as subsidence depressions and ground fissures, will occur.

Restoration of Lake Okeechobee, Florida: mission impossible?

Canfield DE Jr, Bachmann RW, Hoyer MV. 2020. Restoration of Lake Okeechobee, Florida: mission impossible? Lake Reserv Manage. XX:XXX–XXX. Legally mandated eutrophication restoration goals for Lake Okeechobee (FL) are unachievable, therefore assigning managers a “mission impossible.” Since the 1970s, restoration efforts have focused on reducing pelagic total phosphorus (TP) to ∼40 µg/L. A total daily maximum load (TMDL) of 140 metric tons (t)/yr was adopted by the Florida Department of Environmental Protection in 1999 (effective date 2015) to restore the lake’s balance of flora and fauna. Phosphorus (P) loads (1975–2018) averaged 516 t/yr with no significant change over time, yet average TP significantly increased from 51 µg/L (1974–1977) to 146 µg/L (2015–2019). Greater TP values in 2019 were due to Hurricane Irma and an early June storm event. Annual P-loads and pelagic TP were not significantly correlated. Instead, TP was strongly correlated with turbidity (R 2 = 0.85), which is generated by wave-driven resuspension of P-rich unconsolidated sediments. Since 1973, >13,000 t of TP has been added to Okeechobee’s sediments that have accumulated over the past century due to the lowering of water levels and the construction of the Herbert Hoover Dike. Prior to settlement, high water levels allowed turbid lake waters to flood large areas of adjacent wetlands, where suspended sediments were removed from the lake. With the minimization of this self-cleansing mechanism after construction of the Herbert Hoover Dike, P-rich fine sediments accumulated, and periodic hurricanes disrupted consolidated sediments. Unconsolidated sediments are easily resuspended into the water column, raising TP. Efforts to reduce Okeechobee’s pelagic TP through reductions of P-loads alone will not work due to sediment accumulation and resuspension.

Shaking Water Out of Sands: An Experimental Study

AbstractStrong earthquakes can cause different kinds of hydrological responses, and several mechanisms have been suggested to explain them. Verification of these mechanisms, however, is often lacking. Here we test some hypotheses with a laboratory experiment, in particular the hypothesis that dynamic strain mobilizes trapped water in the unsaturated zone. We construct a sand chamber, partially saturated with water, and subject it to “seismic” shaking of controlled energy. Pore pressure in the saturated and unsaturated zones is monitored before and after shaking. We identify three distinct mechanisms: consolidation of sediments in the saturated zone, release of capillary water from the capillary fringe, and mobilization of isolated pore water in the unsaturated zone. Each mechanism may cause pore pressure in the saturated zone to suddenly increase with shaking, and each may offer new insights to understand the source of the extra water and other shallow hydrological responses that appear after earthquakes.

Land subsidence of the Yellow River Delta in China driven by river sediment compaction

Many of the world's largest deltas are sinking due to multiple natural and anthropogenic causes. This is particularly evident for the modern Yellow River Delta (YRD) in China, which is one of the most dynamic coastal systems on Earth. The YRD has experienced complicated patterns of accretion and erosion as well as significant compaction settlements. However, spatiotemporal variability and the long-term settlement rates law in this complex delta system remain poorly understood. Evidently, the surface settlement is supposedly controlled by a long-term natural compaction process of sediments. We first combined the Small Baseline Subset (SBAS) Interferometric Synthetic Aperture Radar (InSAR) method with a geotechnical model and geological, geomorphological, hydrogeological, and geotechnical data to assess the delta-wide long-term spatiotemporal settlement triggered by the consolidation and compaction of river sediments. The combination of satellite and field observations allows us to gain insights into the primary processes controlling surface movement. A total of seventy-five SAR images acquired by ERS and Envisat from 1992 to 2010 are used to generate three independent interferometric subsets calibrated with leveling to unveil spatiotemporal settlement variability. The densely distributed spatiotemporal measurements enable us to acquire the characteristics of the spatiotemporal variations of land movements. Moreover, the annual average settlement rates are observed within a range of 0 to >30 mm. Results suggest that the relative inland stability of the delta contrasts with the decreasing coastal margin trend at an average annual rate of 15 mm. Moreover, the variability is significantly correlated with the delta evolution and variations in subsoil architecture. A comparative analysis has also been conducted between time series InSAR measurements and the theoretical estimates of settlement derived from the geotechnical model. The strong agreement between the InSAR measurements and the geotechnical modeled results indicates that long-term settlement (in a decade-to-century scale) is primarily driven by the compaction of river sediments. The more the delta sub-lobe was newly formed, the more significant the settlement. Decreasing trends in annual settlement rates from approximately 70 mm to 0 mm in the long-term deposit compaction process are also identified. These findings are useful to understand the YRD morphological evolution and may provide insights into the changes in other deltas worldwide.

Consolidating Waste Slurry by Vacuum Preloading with Flocculation

Anionic polyacrylamide (APAM) and quicklime are used to improve vacuum preloading of waste slurry in Shanghai, China. To investigate the influence of these reagents on waste slurry sediment consolidation, tests on laboratory-scale models with and without the reagents were conducted and the results analyzed. Sediment settling was recorded and used to calculate the water content changes during vacuum consolidation. After vacuum consolidation, the water content of sediment samples collected at different distances from the drain at the center of the model were measured and pore properties were determined by mercury intrusion porosimetry. The tests with and without reagents indicated that anionic polyacrylamide (APAM) and quicklime can decrease the water content of waste slurry and change the slurry's properties. In addition, the results of the settlement analysis were used to investigate the characteristics of vacuum consolidation.

Classification of soft-sediment deformation in carbonates based on the Lower Cretaceous Vigla Formation, Kastos, Greece

Soft-sediment deformation (SSD) structures are widespread within the Lower Cretaceous Vigla Formation (limestones and shales) that are exposed in a 7–10 km long and 100 m high section along the east coast of Kastos Island in the Ionian Sea. SSD was observed both in limestones and in shales, and formed during or immediately after deposition, during the first stage of sediment consolidation. They are classified into six (6) different types of deformations: (1) Thick synclines and anticlines, formed due to strong synsedimentary deformation, that were produced mostly from N-S directed normal faults or from the interaction between normal and transfer faults, and are situated between undeformed horizons. (2) Thin slumps ascribed to normal fault activity and especially slumping in the footwall of the active fault, prograding orthogonal to the fault direction. (3) Thin to medium slumps produced from the synsedimentary interaction of N–S normal faults and E–W directed transfer faults, showing multiply directions of progradation. (4) Thin SSD related to diapiric intrusions that also associated with fault activity. (5) Thick slump horizons displaying erosional contacts with the neighboring undeformed limestones in the same horizon, resulting from gravity-driven mass-transport deposits that flowed across inclined basin floors. (6) Thin slumps, with chert nodules, within a slumped horizon, resulting from a slumping phase both after the sedimentation and after early diagenesis in carbonates deposits, but during the sedimentation of the lower Cretaceous Vigla limestones. All the above categories were characterized as seismites or deformation due to fault activity. This tectonism resulting in tilted blocks, the creation of space in hangingwall downthrown blocks, and changes of inclination of the basin floor, outcrops with high lateral extent in different directions adds constraints to the geometry of slumps. The transition zone between Vigla limestones and shales showed particularly abundant deformation structures. Although the Vigla Formation limestones have low primary porosity, the presence of many SSD horizons could increase secondary porosity in this formation.

Load-bearing characteristic of methane hydrate within coarse-grained sediments – Insights from isotropic consolidation

Gas hydrate, as a solid pore constituent, can potentially share external load with sediment matrix, and critically impact geological evolution of its hosting sediments, well integration and sediment settlement during gas production depending on its contribution to support external loading. We aim to address the question of whether hydrate shares the load with the soil skeleton through isotropic consolidation experiments. Our results highlight the formation of methane hydrate does not affect the integrity of sediment skeletons if the effective stress previously applied on the skeleton remains constant, which indicates that methane hydrate would not actively support the load. Subsequent external load applied to the sediments after hydrate formation can be supported by hydrate. Secondly, hydrate as well as hydrate-bearing sediments exhibit creep behavior. As hydrate creeps, the load transfers to the sediment skeleton with time and hydrate gradually retreats from the status of load-bearing. When hydrate saturation is low and the coexisting pore fluid can percolate through sediments, the local deformation of hydrate due to sediment consolidation induces excess pore pressure, which dissipates by pushing out the pore fluid. When the coexisting pore fluid is enclosed in hydrate mass in high hydrate saturation environments, the dissipation of excess pore pressure relies on the viscous flow of hydrate. This pressure dissipation could last for millions of years according to analytical analysis based on Terzaghi's consolidation theory, during which hydrate cannot completely escape the status of load-bearing. These observations conclude that load-bearing is a dynamic status rather than a stagnant pore habit, countering conventional thinking that load-bearing joins grain-coating, cementing and pore-filling as a pore habit of gas hydrate.

Sediment consolidation in ephemeral river: the effect of applied loading on soil properties and dredging method selection

ABSTRACT Bengawan Solo River, a typical large ephemeral river in Indonesia, is facing stream problems induced by the erosion and deposition of sediment. Imbalance between these two phenomena on the riverbed can lead to excessive sedimentation, increased risk of flooding, and formation of sandbars. One proposed solution to address this problem is dredging. However, this process can have potential negative effects on the environment, such as removal or destruction of the biota in the dredged materials, increased turbidity, as well as coverage of the benthos in the vicinity. Also, different dredging methods are needed to suit sediments with different properties. Therefore, the knowledge of the deposited sediment properties is required so that appropriate methods can be selected. The sediment characteristics were obtained by performing laboratory tests on physical and consolidation properties and shear strength tests of a soil sample. The results indicate that the materials were broadly grouped into sandy sediment in downstream areas and clayey sediment in estuary areas. The distribution of sediment properties varies with depth because of subsequent erosion and deposition over time. Additionally, the distribution also shows that sand content decreases as the origin of sample approaches estuary areas. Erosion is predominant at locations with small hydraulic radius and high flow velocity, mostly at downstream areas, whereas deposition is predominant at locations with a large hydraulic radius and low flow velocity, specifically at estuary areas. The shear strength increases as the loads imposed by the self-weight of sediment layer increase. The analysis suggests that sediments cannot be eroded naturally as they have a shear strength that exceeds the small-capacity dredging method (); therefore, the removal of excess sediment in such areas requires dredging methods of larger capacities (such as grab dredger).

The problem of genesis of quaternary deposits of the Barents Sea as a reflection of the overall crisis of glacial theory

This article continues the discussion on quaternary geology and paleogeography of the vast and well-studied shelf of the Barents Sea. The object this research is the relief and quaternary formations of the Barents shelf. The data of seismic-acoustic profiling and materials of engineering-geological drilling were used. Since the Barents shelf is a high-latitude area of Holocene sedimentation, the author analyzes various aspects of the quaternary sediments genesis, taking into account the geographic zoning of marine sedimentation processes and an increase in the gravitational consolidation of sediments down through the section. The genetic link between the microstructure and the degree of consolidation of clayey sediments with their seismic image was revealed, which was considered in interpretation of seismic profiling materials. Over the Barents shelf, the cover of weakly consolidated sediments of the last marine transgression is separated from the underlying morainelike or pre-quaternary sediments by a diachronous boundary of stratigraphic and sometimes angular unconformity. The transgression is not of glacioeustatic, but of tectonic nature. During the hiatus that preceded it, an erosional relief with river valleys and their tributaries was formed, the main features of which have been preserved in the northern deep-water part of the sea. The conclusion is argued that approbation of the glacial theory on the example of high-latitude Arctic shelf contradicts the facts and main provisions of glaciology, reflecting the overall crisis of this theory.

Rapid consolidation characteristics of Yellow River-derived sediment: Geotechnical characterization and its implications for the deltaic geomorphic evolution

The Yellow River, which presently discharges into the western Bohai Sea, has been widely recognized as having one of the highest sediment loads on Earth. Understanding the consolidation characteristics of Yellow River-derived sediments is critical for improving our knowledge of the riverine sediment transport, depositional processes, and evolution of the Yellow River Delta morphology. In this study, we conducted in situ experiments from 2004 to 2008 at an abandoned subaqueous delta lobe (Diaokou lobe) in order to investigate the consolidation process of the sediments. Our results show that the initial consolidation of Yellow River-derived sediment is a rapid process when the excess pore-water pressure caused by sediment aggradation can completely dissipate in ~1500 min. The change in the physical and geotechnical properties during the consolidation endows the sediments with a certain shear strength. However, due to the hydrodynamic conditions, the distribution of the sediment strength is both temporally and spatially inhomogeneous. Furthermore, a hard layer can develop at the depths of 10–30 cm and the adjacent layer can become a potential sliding surface. This study offers some insight into the formation and evolution processes of the Yellow River Delta's sedimentary and geomorphic forms.

Mechanical and hydrological effects of seamount subduction on megathrust stress and slip

Subduction of rough seafloor and seamounts is thought to impact a broad range of geodynamic processes, including megathrust slip behaviour, forearc fluid flow and long-term structural evolution in the overriding plate. Although there are many conceptual models describing the effects of seamount subduction, our quantitative and mechanistic understanding of the underlying deformation and fluid processes remains incomplete. Here we investigate the interplay between sediment consolidation, faulting and the evolution of stress and pore fluid pressure in response to seamount subduction, using a numerical model that couples mechanical and hydrological processes and is constrained by laboratory and field observations. Our results show that subducting topography drives marked spatial variations in tectonic loading, sediment consolidation and megathrust stress state. Downdip of a subducting seamount on its leading flank, enhanced compression and drainage lead to large fault-normal stress and overconsolidated wall rocks. A stress shadow in the seamount’s wake leads to anomalously high sediment porosity. These variations help explain observed patterns of megathrust slip, with earthquakes and microseismicity favoured at the downdip edge of seamounts and aseismic or slow slip in the updip stress shadow. Changing stresses and pore fluid pressures during subduction of seamounts, as simulated with a numerical model that couples mechanical and hydrological processes, help explain observed patterns of megathrust slip.