Shallow Regions Research Articles

Bottom Topography Effect on the Seasonal Mode Generation of the Tsugaru Warm Current

Abstract Several regions in the World Ocean are known to exhibit eddies with characteristic structures controlled by bottom topography and surrounding currents. Here, we analyzed the generation of one such eddy, an anticyclonic gyre that seasonally forms the gyre mode (GM) of the Tsugaru Warm Current (TWC) along its path downstream of the Tsugaru Strait. This eddy greatly influences surface temperature and water mass distributions in this region of high fishery productivity. We constructed composite fields based on relative vorticity for both the GM and the coastal mode (CM) of the TWC, when it flows directly along the meridional Sanriku coast downstream of the strait. Within the strait, the CM-composite path is known to be located south of the GM-composite path. We found that clockwise turning of the barotropic CM-composite flow in shallow regions due to potential vorticity conservation generates the southward components of the outflow from the strait, connecting it smoothly to the meridional coastal current. In contrast, the rather baroclinic GM-composite flow is affected by the topography only near the bottom; as a result, it flows eastward from the strait, where the gyre is generated as has previously been investigated analytically and in laboratory experiments. We also found that the gyre includes both an isolated circulation surrounded by the TWC path and a lower layer with an isopycnal surface depression down to about 1000-m depth. This deep structure is supported by observation data.

Carbon storage and sequestration of five planting patterns of Picea crassifolia plantations in Qilian mountains

Forest plantations play a critical role in mitigating climate change, with their carbon storage and sequestration capacity significantly influenced by planting patterns. This study focuses on Picea crassifolia plantations in the shallow mountainous region of the Qilian Mountains, aiming to investigate the effects of five planting patterns (pure forests, mixed forests, and uneven-aged forests) on vegetation and soil organic carbon (SOC) dynamics. The research provides a scientific basis for optimizing forest management strategies in arid and semi-arid regions. Fifteen sample plots were established in the Qilian Mountains, Gansu Province, covering five planting patterns: pure forests with 1.5 × 1.5 m (P1.5) and 2 × 2 m (P2) spacing, uneven-aged pure forests (PX), mixed forests of P. crassifolia and Pinus sylvestris var. mongholica (PC), and mixed forests of P. crassifolia, P. sylvestris, and Caragana korshinskii (PPC). Vegetation biomass (tree height, DBH, crown width) and soil samples (0 – 80 cm depth) were collected. Carbon content was determined using the potassium dichromate oxidation method, and carbon stocks were estimated using national biomass models. Statistical analyses (one-way ANOVA) and membership function evaluation were applied to assess carbon sink potential. Results showed that: 1. Planting spacing: The 2 × 2 m pure forest (P2) exhibited higher vegetation-layer carbon storage (10 t·ha−1) compared to the 1.5 × 1.5 m pure forest (P1.5, 5 t·ha−1). 2. Age heterogeneity: The uneven-aged pure forest (PX) showed the highest vegetation-layer carbon storage (6.61 t·ha−1), but its total carbon stock (106.98 t·ha−1) was slightly lower than P2 (111.08 t·ha−1) due to P2’s superior SOC content in deeper soil layers (13.64 g·kg−1 at 60–80 cm). 3. Pure vs. mixed forests: Pure forests (P2) outperformed mixed forests (PC, PPC) in total carbon storage, driven by soil-layer contributions (>95% of total stocks). The 2 × 2 m pure forest (P2) demonstrated optimal carbon sequestration potential in the Qilian Mountains, with soil carbon dominance highlighting the importance of deep-layer SOC accumulation. While uneven-aged forests (PX) showed strong vegetation carbon storage, long-term carbon sinks require integrated soil management. These findings provide critical insights for arid-region plantation configurations. Future studies should combine remote sensing for dynamic carbon monitoring and explore diversified mixed-species systems to enhance ecosystem stability.

First Observations of a Deep-Water Seagrass Meadow (Thalassodendron ciliatum) on an Oceanic Reef in the Southern Coral Sea Marine Park, Australia.

Tropical seagrass meadows are important global marine ecosystems that provide critical ecosystem goods and services. The extent of global seagrass meadows is mostly mapped from shallow coastal regions and not well known or sampled from deeper offshore locations. Seagrasses can, however, form deep-water meadows, which likely significantly increase the total area of global seagrass ecosystems and may contribute important ecological functions to offshore tropical seascapes. Here we report the first observation of a dense meadow of Thalassodendron ciliatum at a depth of 25 m using remotely operated vehicles (ROVs) from the Coral Sea Marine Park (CSMP). Despite significant survey effort in the region, to date there have only been three other observations of seagrass in the CSMP, all sparse and small patches of Halophila ovalis and Halophila decipiens. We discuss the significance of this newly discovered meadow within the context of current reef health monitoring of the CSMP, reef fish biodiversity and the ecological value of deep-water seagrass habitats for offshore coral reef systems like the Coral Sea.

A Succession of Microbiome Communities in the Early Establishing Process of an Epilithic Algal Matrix in a Fringing Reef.

An epilithic algal matrix (EAM) exhibits rapid expansion, recovery capacity, and high adaptability, leading to widespread distribution in degraded coral reef habitats. However, limited research on the dynamic processes of succession hinders a comprehensive understanding of EAM formation. To examine the influence of succession processes and environmental factors on the composition of EAM microbial communities, a three-factor (time × depth × attached substrate type) crossover experiment was conducted in the Luhuitou Reef Area, Sanya, China. Microbial community compositions were analyzed through 16S rRNA gene amplicon sequencing. The community was predominantly composed of proteobacteria (61.10-92.75%), cyanobacteria (2.47-23.54%), bacteroidetes (0.86-8.49%), and firmicutes (0.14-7.76%). Successional processes were found to significantly shape the EAM-associated microbial communities in the Luhuitou Reef Area. Proteobacteria played a crucial role in biofilm formation during this process, while cyanobacteria contributed to the structural complexity of microhabitats within the EAM. A chaotic aggregation stage of approximately one month was observed before transitioning into an expansion stage, eventually stabilizing into a low-diversity community. Although the relatively smooth substrate supported high biodiversity, microorganisms displayed no preference for the three different substrates. While no significant differences in community composition were observed at small-scale depths, cyanobacteria and bacteroidetes showed positive correlations with light and temperature, respectively. The EAM-associated microbial community exhibited higher complexity in the shallower regions under increased light intensity and temperature. Given the characteristics of the microbial community succession process, continuous monitoring of changes in microbial community structure and key taxa (such as proteobacteria and cyanobacteria) during EAM formation is recommended.

Optimizing crop management strategies for improved yield, water productivity, and sustainability of quinoa in shallow basaltic semi-arid regions.

Recently, quinoa (Chenopodium quinoa Willd.) has gained global recognition as a nutritious, adaptable crop suitable to adverse soil and climatic conditions. However, knowledge about optimal management practices for its cultivation in marginal areas of India is limited. In this context, a field experiment was conducted in a split-split plot design with four sowing dates (D1: 1st November; D2: 15th November; D3: 1st December, D4: 15th December) in main plots, two irrigation levels (I1: 40% ETc; I2: 80% ETc) in sub-plots, and three nitrogen doses (N1: 100 kg N ha-1; N2: 150 kg N ha-1; N3: 200 kg N ha-1) in sub-sub plots having three replications during 2021-22 and 2022-23 in shallow basaltic murram soils. Results indicated that sowing on 1st November yielded the highest seed production of 1446 kg ha-1, as temperatures aligned closely with optimal growth conditions. Quinoa's drought tolerance meant that deficit irrigation was able to maintain the crop growth and yield. While the crop responded positively to higher N doses, the study found that applying 100 kg N ha-1 was optimal, considering shallow basaltic soil conditions and potential lodging issues. Additionally, water productivity, protein, and saponin content reflected similar trends to seed yield. The results suggested that early sowing, irrigation at 40% ETc, and 100 kg N ha-1 produced a seed yield of 1446 kg ha-1, demonstrating higher carbon efficiency and sustainability while minimizing N2O emissions. However, these strategies should be tailored to specific agro-ecological conditions. Overall, the findings confirm quinoa's potential for cultivation in India's 26 million hectares of shallow basaltic murram soils, where other crops may not thrive economically.

Theoretical Investigation of NH3 and NO2 Affinity Towards Boron-nitride Nanosheet: A Dft Study

Background: Two-dimensional (2D) nanosheets have been widely explored for sensing toxic gases by investigating structural and electronic properties. However, the optical investigation could be an alternative approach to address the sensing capability of the nanosheets. In the present work, the electronic and optical investigation is performed using density functional theory (DFT) to find out the sensitivity of boron-nitride nanosheet (BNNS) towards NH3 and NO2 gas molecules. Electronic investigation suggests a weak binding of NH3 and NO2 with the 2D sheet, with appreciable changes in the BNNS electronic density of state (DOS) on NO2 interaction. NH3 interaction could not affect the BNNS DOS except for lowering of band dispersion graph across the Fermi level. NO2 interaction brings a noticeable change in spectra, primarily red-shift. Based on this information, tuning is also observed in different optical descriptors, i.e., dielectric constant, refractive index, and extinction coefficient of NO2 interacted BNNS. All these findings advocate sensitivity toward the gas molecule of the 2D sheet could be realized from the optical frame. Objective: Finding NH3 and NO2 affinity of Boron-Nitride Nanosheet Through Optical Spectrum: A DFT Study. Methods: The calculations are performed in the framework of density functional theory (DFT) using Troullier Martins’s norm-conserving pseudo-potential. Results: The NO2 interacted BNNS shows the optical spectra get red-shifted, and the primary reason is the available NO2 molecular state below the fermi level as shown in PDOS analysis. Conclusion: The present investigation predicted an almost similar ε2 spectra pattern of BNNS and NH3-BNNS except in shallow region 7 eV-10 eV; a weak absorption band appeared in this region after NH3 absorption. The main concern for this deviation is the electronic transitions taken from the valance N-p-state of NH3 to the conduction band (primarily π* in nature) of BNNS.

Coupled Hydrodynamic and Habitat Suitability Models for Reach‐Scale Restoration of Wintering Waterbird Habitats in Rivers: A Case Study on Scaly‐Sided Merganser

ABSTRACTRivers are pivotal ecosystems for migratory waterbirds, with the habitat preferences of piscivorous species heavily influenced by hydrodynamic factors such as water depth and flow velocity. These variables directly impact food availability and the foraging behaviours of waterbirds. While the integration of hydrodynamic and habitat suitability models has been effective in assessing river conditions and guiding restoration efforts, research specific to instream‐dependent piscivorous waterbirds at the reach scale is scarce. This research concentrates on the scaly‐sided merganser (Mergus squamatus), an endangered species on the IUCN Red List, identifying crucial habitat factors—water depth, flow velocity and human disturbance distance—based on their significance in shaping wintering habitat choices for this bird. Through a coupled hydrodynamic habitat suitability model deployed in a segment of the Xitiaoxi River in southeastern China, the study seeks to create a tailored model for the scaly‐sided merganser, assess distribution and landscape features of suitable instream habitats and suggest restoration and management tactics. Results show that despite the dry season revealing suitable areas for water depth (31.1%), flow velocity (16.8%) and human disturbance (80.5%) respectively, the combined suitable habitat only occupies 5.1%, predominantly in shallow regions like riffles and sandbanks. The study proposes strategies to enhance habitat suitability for the scaly‐sided merganser, presenting a pragmatic approach for reach‐scale river restoration, management and proactive conservation efforts beneficial for waterbirds. The findings are relevant not only for southern rivers in China but also for rivers in other countries that support migratory waterbirds and similar piscivorous waterbird habitats.

Decoding the drivers of variability in chlorophyll-a concentrations in the Pearl River Estuary: Intra-annual and inter-annual analyses of environmental influences.

Decoding the drivers of variability in chlorophyll-a concentrations in the Pearl River Estuary: Intra-annual and inter-annual analyses of environmental influences.

Impact of topographic change on the East Asian monsoon in Japan and Eastern Asia during the Last Glacial Maximum

The rainfall patterns in Eastern Asia are largely a consequence of the Asian winter and summer monsoons. On timescales 104–106 of years, the position and strength of the monsoons change as a result of variations in Northern Hemisphere summer insolation. However, locally, it is possible there is a superimposed signal due to sea level change. Due to the growth of ice sheets, primarily in northern North America and Europe, global average sea level fell about 120 m during the Last Glacial Maximum (27,000–19,500 years ago). This caused the broad shallow continental shelf regions in coastal Eastern Asia to be exposed, and also greatly limited the flow of warm Pacific water into the Sea of Japan. In this study, we perform climate modelling experiments to isolate the impact of the lower sea level on the rainfall patterns in Eastern Asia. We find that the lowered sea level locally increases the summer precipitation, impacting the southern parts of Japan as well as Eastern China. The lower sea level also causes a decrease in winter precipitation in Japan. Our oxygen isotope modelling results show that the lower sea level alone is sufficient to explain the extremely depleted δ18O values measured from proxies in Last Glacial Maximum sediments in the Sea of Japan. These results show that the rainfall proxy records in the coastal Eastern Asia region, especially near the East China Sea, should not be interpreted as purely due to insolation driven changes to the monsoon front, as they also contain a local signal due to sea level changes. Further impacts of sea level changes on continental proxy records are likely limited, and they are measuring a purely global climate change signal.

Sun Glint-Aware Restoration (SUGAR): a robust sun glint correction algorithm for UAV imagery to enhance monitoring of turbid coastal environments.

Sun glint contamination on unmanned aerial vehicles (UAV) imagery is a ubiquitous problem and poses a significant impediment in the retrieval of water quality parameters for coastal monitoring applications. Previous studies using near-infrared (NIR) and regression-based sun glint corrections have shown overcorrection at turbid regions as water-leaving NIR radiance is non-negligible. A spatial shift in the band channels would also result in suboptimal correction in the visible spectrum. Recent total variation (TV) methods show promise in reducing spectral variation associated with glint-affected regions and achieve effective correction of sun glint while leaving non-glint regions largely unaltered. To that end, this study proposes an open-source Sun Glint-Aware Restoration (SUGAR) algorithm that bridges principles in NIR and TV methods for the effective correction of sun glint in multispectral and hyperspectral UAV imagery. The present study shows that SUGAR achieves the best sun glint correction performance among existing regression and pixel-based sun glint correction methods when applied on UAV imagery of turbid and shallow regions. Around 40-80% of the total variation at glint-affected regions have been reduced while preserving features in non-glint regions. Validation of SUGAR with in situ UAV flight surveys and turbidity measurements in the coastal region of Singapore demonstrated significant improvement in turbidity retrieval, with root-mean-squared error (RMSE) reducing from 0.464 to 0.183 FNU and 0.551 to 0.285 FNU for multispectral and hyperspectral imagery, respectively.

Comparison of UAV-based digital elevation model with multi beam bathymetry for shallow water

Accurate bathymetric data is essential for marine and coastal applications, particularly in shallow water regions. Unmanned Aerial Vehicle (UAV)-based systems are recognized for their cost-effectiveness and flexibility, making them a promising alternative in shallow-water environments where Multi Beam Echosounder (MBES) systems often face limitations due to high operational costs or logistical challenges. However, the UAV-based method is influenced by refraction effects, which result in underwater objects being perceived as shallower than their actual depth, leading to a decrease in the accuracy of the bathymetric model. To address this issue, the underestimation of water depth in submerged areas caused by refraction was evaluated using a correction algorithm. This study aims to assess the accuracy and usability of the UAV-based Digital Elevation Model (DEM) for seafloor mapping. For this assessment, the UAV-based DEM from the water body was compared with high-resolution three-dimensional (3D) seafloor topography obtained from a multi beam acoustic survey conducted in the same water area. The results indicated that an accuracy of 1.2 meters (RMSE) can be achieved in relatively shallow water areas up to a depth of 5 meters, while an accuracy of 2.0 meters (RMSE) is achievable at depths of around 15 meters. The study also highlighted the direct correlation between UAV-based DEM accuracy and depth, as well as the impact of sun glint on measurement accuracy. These findings underscore the potential of UAV technology to enhance bathymetric surveying capabilities, particularly in regions where MBES is either impractical or cost-prohibitive, thereby offering a valuable tool for comprehensive mapping and coastal studies

Multiattribute analytics of polka-dot anomalies in the Yeongil Bay, South Korea

The shallow region of a three-dimensional seismic dataset acquired in Yeongil Bay, Pohang exhibits various interesting features. In particular, the region exhibits bright circular seismic amplitude anomalies. These anomalies are located in a topographic low of the seismic data surrounding the structural high from the northern, southern, and eastern ends. The anomalies are confined to a temporal region of the seismic data and exhibit a concave-down appearance when viewed in cross-section. Although such bright seismic amplitudes can often be a direct indicator of hydrocarbon presence, to avoid misinterpreting this feature, multiattribute analyses are applied to the data. The abnormal structural characteristics are further examined by applying a geometric attribute analysis to emphasize the coherency of the signals within the region of anomaly distribution. We also apply a physical attribute analysis to determine that these anomalies can result from the changes in lithology, most likely a sandy formation, which can be inferred from a stratigraphic analysis of the Pohang Basin. Recent findings suggest the possibility of hydrocarbon presence in the study region, but we cannot rule out other possibilities without well-log data to specify the physical characteristics.

Sulfur partitioning between aqueous fluids and felsic melts at high pressures: Implications for sulfur migration in subduction zones

Sulfur (S), an essential volatile in subduction zone magmatism, exhibits higher solubility in aqueous fluids compared to silicate melts. Despite its importance, the partitioning of S between aqueous fluids and silicate melts under the conditions of subduction zone, critical for magma generation and evolution, remains poorly understood. To address this knowledge gap, we performed piston-cylinder experiments at a temperature of 950 ℃ and pressures of 1 and 2 GPa, investigating the effects of various parameters including oxygen fugacity, melt composition, fluid composition (salinity) and pressure on S partitioning between aqueous fluid and silicate melt (DSfluid/melt). Our results indicate that the DSfluid/melt is always large (> > 1), and S prefers to enter the aqueous fluid at high pressures. However, the DSfluid/melt decreases with increasing pressure from 1 to 2 GPa. Specifically, under reducing conditions (Ni-NiO buffer), DSfluid/melt decreased from 147 ± 40 to 20 ± 2, whereas under moderately oxidizing conditions (Re-ReO2 buffer), it decreased from 27 ± 1 to 20 ± 2. These results stress the strong affinity of S for aqueous fluids at high pressures. Together with the great capacity for S dissolution in the H2O-rich magma within the deep Earth, fluid-saturated felsic magma efficiently transports substantial amounts of S from deep to shallow regions in subduction zone settings. This process plays a crucial role in the formation of giant porphyry deposits and provides a potential source of excess S released during explosive volcanic eruptions.

Modulating the Selective Enrichment and Depletion of Ions Using Electrorheological Fluids in Variable-Area Microchannels.

Electrorheological fluids are suspensions that are characterized by a strong functional dependence of their constitutive behavior on the local electric field. While such fluids are known to be promising in different applications of microfluidics including electrokinetic flows, their capabilities of controlling ion transport and preferential solute segregation in confined fluidic systems remain to be explored. In this work, we bring out the unique role of electrorheological fluids in orchestrating the selective enrichment and depletion of charged species in variable area microfluidic channels. Our reported phenomenon is fundamentally distinctive from other types of nonlinear electrokinetic effects previously reported, in a sense that here the dependence of the flow rheology on the electric field turns out to be the central mechanism toward orchestrating the observed nonlinear ion transport. Our results indicate exclusive features of the resulting ion concentration polarization, such as more pronounced ion concentration polarization, controlled largely by the influence of the variations in the channel cross section on the driving electrokinetic forces and the resistive viscous interactions. The underlying physical mechanism is captured aptly by a simple one-dimensional area-averaged model, and validated by full-scale three-dimensional simulations. Our illustrative case study for a converging-diverging microchannel with cross-sectionally uniform solute concentrations reveals that electrorheological effect with greater contrast between the deep and shallow region depths, greater solute concentration, and larger applied axial electric field, all acting in tandem, magnifies the solute enrichment and depletion in the respective segregation zones, bearing significant implications in analytical chemistry, bioanalysis, and beyond.

Three-Dimensional Particle Tracking Velocimetry Investigation of Flow Dynamics Around Simplified Stones at Low Submergence: Implications for Instream Habitat

Shallow waterways such as rapids, tributaries and smaller streams can have important ecological functions in both free-flowing and regulated rivers. As more intermittent renewable energy is introduced to the energy system to reduce CO2 emissions, the operational conditions of hydropower plants are changing. This implies various flow scenarios that can lead to more locations with shallow depths and larger variations in water levels and velocities, resulting in increased impact on the riverine ecosystem. Accurate predictions of these impacts require an understanding of the flow dynamics near large roughness elements such as boulders or trees in shallow river regions. This study uniquely investigates the effect of relative submergence, i.e., water depth relative to boulder size, on the flow field, turbulence, and potential fish habitats around idealized stone shapes (hemispheres) in shallow open channel flow using time-resolved 3D particle tracking velocimetry. The results indicate that varying relative submergence significantly affects recirculation zones, velocity and vorticity distribution, as well as turbulent kinetic energy. Notably, larger regions of lower velocity downstream of the roughness elements were generated at lower submergences, which might be favorable for fish energy conservation. Valuable insights into ecohydraulic engineering and habitat restoration in shallow waterways can be gained by understanding the fundamental flow mechanisms at low submergence for the flow around large roughness elements.

Seismic response and damage model analysis of rocky slopes with weak interlayers

Abstract A large-scale shaking table test of an anti-dip rock slope with a weak interlayer is conducted based on the Hongshiyan landslide induced by the Ludian earthquake. The dynamic failure mode energy damage identification method is analyzed using the Hilbert–Huang transformation and marginal spectrum theory. The result shows that the weak interlayer under horizontal loading amplifies the 5–10 and 25–30 Hz frequency signal and attenuates the 15–20 Hz signal. Within the hard rock, it amplifies the 5–15 Hz frequency signal and attenuates the 20–30 Hz signal. Under vertical loading, both weak interlayer and hard rock have an amplification effect on 5–30 Hz signal, and the amplification effect of weak interlayer is more significant. The horizontal seismic wave slope damage process can be divided into two stages: internal damage and obvious failure. When the horizontal seismic input amplitude reaches 0.2–0.3 g, internal damage occurs in the slope. The slope damage is primarily concentrated below two-third of the hard rock height and primarily in the shallow and surface regions of the slope. An input amplitude in the range of 0.4–0.5 g corresponds to the obvious failure stage. At this time, the slope first undergoes an obvious rupture in the rock above the weak layer; this rupture then extends upward to the top of the slope. Marginal spectral analysis results are consistent with the field model slope macroscopic rupture phenomenon.

Estimating ocean heat content from the ocean thermal expansion parameters using satellite data

Abstract. Ocean heat content (OHC) is a depth-integrated physical oceanographic variable used to precisely measure ocean warming. Because of the limitations associated with in situ conductivity, temperature, and depth (CTD) data as well as ocean reanalysis system products, satellite-based approaches have gained importance in estimating the daily to decadal variability of OHC over the vast oceanic region. Efforts to minimize the biases in satellite-based OHC estimates are needed to realize the actual response of the ocean to the brunt of climate change. In the current study, an attempt has been made to better implement the satellite-based ocean thermal expansion method to estimate OHC at 17 depth extents ranging from the surface to 700 m. To achieve this objective, artificial neural network (ANN) models were developed to derive thermosteric sea level (TSL) from a given dataset of sea surface temperature, sea surface salinity, geographical coordinates, and climatological TSL. The model-derived TSL data were further used to estimate OHC changes based on the thermal expansion efficiency of heat. Statistical analysis showed high correlation coefficients and low errors in the validation of model-derived TSL and OHC for the 700 m modeling depth (N 388 469, R 0.9926 and 0.9922, RMSE 1.16 m and 1.56 GJ m−2, MBE −0.19 m and −0.24 GJ m−2, MBPE −0.46 % and −0.03 %, MAE 0.76 m and 1.03 GJ m−2, and MAPE 2.34 % and 0.13 %) and nearly similar results at the remaining modeling depths. These results suggest that the proposed ANN models are capable of generating satellite-based daily OHC maps by covering both shallower and deeper oceanic regions of varying bathymetry levels (≥20 m). In addition, the first-ever attempt to estimate the ocean thermal expansion component (i.e., TSL) from satellite data was successful, and the model-derived TSL can be used to obtain high-end sea level rise products in the global ocean.

Probabilistic estimation of rheological properties in subduction zones using sequences of earthquakes and aseismic slip

Abstract Constraining the effective rheology of major faults contributes to improving our understanding of the physics of plate boundary deformation. Geodetic observations over the earthquake cycle are often used to estimate key rheological parameters, assuming specific laboratory-informed classes of viscous or frictional rheological models. However, differentiating between various rheological model classes using only observations of a single earthquake (coseismic and postseismic deformation) is difficult—especially in the presence of coarse spatiotemporal sampling, inherent observational noise, and non-uniqueness of the inverted properties. In this study, we present a framework to estimate key rheological parameters of a subduction zone plate interface using simulations of sequences of earthquakes and aseismic slip, constrained by pre- and postseismic surface displacement timeseries. Our simplified forward model consists of a two-dimensional subduction zone, represented by a discretized planar fault or narrow shear zone, divided into a locked, shallow region (“asperity”) experiencing periodically imposed coseismic events, and a stress-driven creeping section governed by power-law viscoelasticity or rate-dependent friction. Our inverse model fits the rheological parameters of the interface to surface displacement timeseries in a Bayesian probabilistic way. We validate that our proposed framework can successfully recover depth-dependent profiles of effective viscosity using a synthetic dataset of pre- and postseismic observations. Our first set of numerical experiments show that our framework is only mildly sensitive to uncertainties in the rupture history or assumed coseismic slip, making it robust enough to be applied to real observations of subduction zones. Our second set of tests considers the similarities of surface displacement timeseries between synthetic models that model the plate interface either as a shear zone described by power-law viscosity, or a surface described by rate-dependent friction. Here, we find that the ability to fit surface observations using functional or mechanical models assuming frictional behavior does not constitute sufficient evidence to actually infer frictional behavior at depth, as the surface expressions are virtually indistinguishable from deformation generated from models with depth-variable power-law viscous behavior. Based on our numerical experiments, we conclude that studies that aim to infer the mechanical behavior and rheological properties at depth in subduction zones should consider the surface expression from time periods representative of the entire seismic cycle. Graphical Abstract

Bathymetry estimation for coastal regions using self-attention

Bathymetric mapping of the coastal area is essential for coastal development and management. However, conventional bathymetric measurement in coastal areas is resource-expensive and under many constraints. Various research have been conducted to improve the efficiency or effectiveness of bathymetric estimations. Among them, Satellite-Derived Bathymetry (SDB) shows the greatest promise in providing a cost-effective and efficient solution due to the spatial and temporal resolution offered by satellite imagery. However, the majority of the SDB models are designed for regional bathymetry, which requires prior knowledge of the tested region. This strongly constrains their application to other regions. In this work, we present TransBathy, a deep-learning-based satellite-derived bathymetric model, to solve the coastal bathymetric mapping for different unknown challenging terrains. This model is purposefully crafted to simultaneously assimilate deep and spatial features by employing an attention mechanism. In addition, we collected a large-scale bathymetric dataset covering different shallow coastal regions across the world, including Honolulu Island, Abu Dhabi, Puerto Rico, etc. We trained the model using the collected dataset in an end-to-end manner. We validated the robustness and effectiveness of our model by conducting extensive experiments, including pre-seen and un-seen regions bathymetric estimations. When testing on pre-seen coastal regions in different locations of the world, our model achieves a good performance with an RMSE m and R2 in the depth down to m. When testing in challenging unseen coastal regions with different bottom types, our model obtains RMSE m and R2 in the steep slope region with depth down to m and obtains RMSE m and R2 in the rugged region with depth down to m. Our model even surpasses the baseline SDB method that is pre-trained in these regions by substantially reducing the RMSE by 0.978m and improving the R2 by 0.187 in the steep slope region. The dataset, code, and trained weights of the model are publicly available on GitHub.

Optimizing composite ecological networks through Synergistic risk Management, ecological Conservation, and recreational Integration: A case study of Beijing’s shallow mountain regions

Optimizing composite ecological networks through Synergistic risk Management, ecological Conservation, and recreational Integration: A case study of Beijing’s shallow mountain regions